Unit III- IV Java

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Unit III

Applet Programming:

A Java applet is anappletdelivered to users in the form ofJava bytecode. Java applets can run in

aWeb browserusing aJava Virtual Machine(JVM), or inSun'sAppletViewer, a stand-alone tool for

testing applets. Java applets were introduced in the first version of the Java language in 1995, and

are written inprogramming languagesthat compile to Java bytecode, usually inJava, but also in other

languages such asJython,[8]

JRuby,[9]

orEiffel(viaSmartEiffel).[10]

Java applets run at very fast speeds comparable to, but generally slower than, other compiled

languages such asC++, but until approximately 2011 many times faster thanJavaScript.[11]

In

addition they can use 3Dhardware accelerationthat is available from Java. This makes applets well

suited for non-trivial, computation intensive visualizations. As browsers have gained support for native

hardware accelerated graphics in the form ofCanvasandWebGL, as well asJust in Time

compiledJavaScript, the speed difference has become less noticeable.

Since Java'sbytecodeiscross-platformor platform independent, Java applets can be executed by

browsers for many platforms, includingMicrosoft Windows,Unix,Mac OSandLinux. It is also trivial to

run a Java applet as an application with very little extra code. This has the advantage of running a

Java applet in offline mode without the need for any Internet browser software and also directly from

theintegrated development environment(IDE).

Overview

Applets are used to provide interactive features to web applications that cannot be providedbyHTMLalone. They can capturemouse inputand also have controls likebuttonsorcheck boxes. In

response to the user action an applet can change the provided graphic content. This makes applets

well suitable for demonstration, visualization and teaching. There are online applet collections for

studying various subjects, from physics[12]

to heart physiology.[3]Applets are also used to create

onlinegame collectionsthat allow players to compete against live opponents in real-time.

An applet can also be a text area only, providing, for instance, a cross platformcommand-line

interfaceto some remote system.[13]

If needed, an applet can leave the dedicated area and run as a

separate window. However, applets have very little control over web page content outside the applet

dedicated area, so they are less useful for improving the site appearance in general (while applets

likenews tickers[14]

orWYSIWYGeditors[15]

are also known). Applets can also play media in formatsthat are not natively supported by the browser

[16]

HTML pages may embed parameters that are passed to the applet. Hence the same applet may

appear differently depending on the parameters that were passed.

As applets have been available beforeCSS, they were also widely used for trivial effects like

navigation buttons. This use is criticized and declining.[17]

[edit]Technical information

Java applets are executed in asandboxby most web browsers, preventing them from accessing local

data likeclipboardorfile system. The code of the applet is downloaded from aweb serverand the
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browser eitherembedsthe applet into a web page or opens a new window showing the applet'suser

interface.

A Java applet extends the classjava.applet.Applet , or in the case of

aSwingapplet,javax.swing.JApplet. The class must override methods from the applet class to

set up a user interface inside itself (Applet is a descendant ofPanelwhich is a descendantofContainer. As applet inherits from container, it has largely the same user interface possibilities as

an ordinary Java application, including regions with user specific visualization.

The first implementations involved downloading an applet class by class. While classes are small

files, there are frequently a lot of them, so applets got a reputation as slow loading components.

However, sincejarswere introduced, an applet is usually delivered as a single file that has a size

similar to a large image file (hundreds of kilobytes to several megabytes).

Thedomainfrom where the applet executable has been downloaded is the only domain to which the

usual (unsigned) applet is allowed to communicate. This domain can be different from the domain

where the surrounding HTML document is hosted.

Javasystem librariesandruntimesare backwards compatible, allowing to write code that runs both

on current and on future versions of the Java virtual machine.

[edit]Similar technologies

Many Java developers, blogs and magazines are recommending that theJava Web Starttechnology

be used in place of Applets.[18][19]

Java Web Start also allows to launch unmodified applet code, only it

then runs in a separate window (not inside the invoking browser).

AJava Servletis sometimes informally compared to be "like" a server-side applet, but it is different in

its language, functions, and in each of the characteristics described here about applets.

[edit]Embedding into a web page

The applet can be displayed on the web page by making use of the deprecatedappletHTML

element,[20]

or the recommended objectelement.[21]

Embed element can be used[22]

with Mozilla

family browsers (embed was deprecated in HTML 4 but is included in HTML 5). This specifies the

applet's source and location. Object and embed tags can also download and install Java virtual

machine (if required) or at least lead to the plugin page. Applet and object tags also support

loading of the serialized applets that start in some particular (rather than initial) state. Tags also

specify the message that shows up in place of the applet if the browser cannot run it due any reason.

However, despite object being officially a recommended tag, as of 2010, the support of

the object tag was not yet consistent among browsers and Sun kept recommending theolderapplet tag for deploying in multibrowser environments,

[23]as it remained the only tag

consistently supported by the most popular browsers. To support multiple browsers, the object tag

currently requires JavaScript (that recognizes the browser and adjusts the tag), usage of additional

browser-specific tags or delivering adapted output from the server side. Deprecating applet tag has

been criticized.[24]

Oracle now provides a maintained JavaScript code[25]

to launch applets with cross

platform workarounds

Advantages

A Java applet can have any or all of the following advantages:[28]
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It is simple to make it work on Linux, Microsoft Windows and Mac OS X i.e. to make it cross

platform. Applets are supported by mostweb browsers.

The same applet can work on "all" installed versions of Java at the same time, rather than just the

latestplug-inversion only. However, if an applet requires a later version of theJava Runtime

Environment(JRE) the client will be forced to wait during the large download.

Most web browserscacheapplets so will be quick to load when returning to a web page. Applets

also improve with use: after a first applet is run, the JVM is already running and starts quickly (the

JVM will need to restart each time the browser starts afresh). It should be noted that JRE

versions 1.5 and greater stop the JVM and restart it when the browser navigates from one HTML

page containing an applet to another containing an applet.

It can move the work from theserverto theclient, making a web solution more scalable with the

number of users/clients.

If a standalone program (likeGoogle Earth) talks to a web server, that server normally needs to

support all prior versions for users which have not kept their client software updated. In contrast,

a properly configured browser loads (and caches) the latest applet version, so there is no need to

support legacy versions.

The applet naturally supports the changing user state, such as figure positions on the

chessboard.

Developers can develop and debug an applet direct simply by creating a main routine (either in

the applet's class or in a separate class) and calling init() and start() on the applet, thus allowing

for development in their favoriteJava SEdevelopment environment. All one has to do after that is

re-test the applet in the AppletViewer program or a web browser to ensure it conforms to security

restrictions.

Anuntrustedapplet has no access to the local machine and can only access the server it came

from. This makes such an applet much safer to run than a standalone executable that it could

replace. However, a signed applet can have full access to the machine it is running on if the user

agrees.

Java applets are fast - and can even havesimilar performanceto native installed software.

[edit]Disadvantages

A Java applet may have any of the following disadvantages:

It requires the Javaplug-in.

Some browsers, notably mobile browsers runningApple iOSorAndroiddo not run Java applets

at all.[29][30]

Some organizations only allow software installed by the administrators. As a result, some users

can only view applets that are important enough to justify contacting the administrator to request

installation of the Java plug-in.

As with any client-side scripting, security restrictions may make it difficult or even impossible foran untrusted applet to achieve the desired goals. However, simply editing the java.policy file in
http://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Web_browserhttp://en.wikipedia.org/wiki/Plug-in_(computing)http://en.wikipedia.org/wiki/Plug-in_(computing)http://en.wikipedia.org/wiki/Plug-in_(computing)http://en.wikipedia.org/wiki/Java_Virtual_Machinehttp://en.wikipedia.org/wiki/Java_Virtual_Machinehttp://en.wikipedia.org/wiki/Java_Virtual_Machinehttp://en.wikipedia.org/wiki/Web_cachehttp://en.wikipedia.org/wiki/Web_cachehttp://en.wikipedia.org/wiki/Web_cachehttp://en.wikipedia.org/wiki/Server_(computing)http://en.wikipedia.org/wiki/Server_(computing)http://en.wikipedia.org/wiki/Server_(computing)http://en.wikipedia.org/wiki/Client_(computing)http://en.wikipedia.org/wiki/Client_(computing)http://en.wikipedia.org/wiki/Client_(computing)http://en.wikipedia.org/wiki/Google_Earthhttp://en.wikipedia.org/wiki/Google_Earthhttp://en.wikipedia.org/wiki/Google_Earthhttp://en.wikipedia.org/wiki/Java_Platform,_Standard_Editionhttp://en.wikipedia.org/wiki/Java_Platform,_Standard_Editionhttp://en.wikipedia.org/wiki/Java_Platform,_Standard_Editionhttp://en.wikipedia.org/w/index.php?title=Untrusted&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Untrusted&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Untrusted&action=edit&redlink=1http://en.wikipedia.org/wiki/Java_performancehttp://en.wikipedia.org/wiki/Java_performancehttp://en.wikipedia.org/wiki/Java_performancehttp://en.wikipedia.org/w/index.php?title=Java_applet&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Java_applet&action=edit&section=7http://en.wikipedia.org/w/index.php?title=Java_applet&action=edit&section=7http://en.wikipedia.org/wiki/Plug-in_(computing)http://en.wikipedia.org/wiki/Plug-in_(computing)http://en.wikipedia.org/wiki/Plug-in_(computing)http://en.wikipedia.org/wiki/IOS_(Apple)http://en.wikipedia.org/wiki/IOS_(Apple)http://en.wikipedia.org/wiki/IOS_(Apple)http://en.wikipedia.org/wiki/Android_(operating_system)http://en.wikipedia.org/wiki/Android_(operating_system)http://en.wikipedia.org/wiki/Android_(operating_system)http://en.wikipedia.org/wiki/Java_applet#cite_note-29http://en.wikipedia.org/wiki/Java_applet#cite_note-29http://en.wikipedia.org/wiki/Java_applet#cite_note-29http://en.wikipedia.org/wiki/Java_applet#cite_note-29http://en.wikipedia.org/wiki/Java_applet#cite_note-29http://en.wikipedia.org/wiki/Android_(operating_system)http://en.wikipedia.org/wiki/IOS_(Apple)http://en.wikipedia.org/wiki/Plug-in_(computing)http://en.wikipedia.org/w/index.php?title=Java_applet&action=edit&section=7http://en.wikipedia.org/wiki/Java_performancehttp://en.wikipedia.org/w/index.php?title=Untrusted&action=edit&redlink=1http://en.wikipedia.org/wiki/Java_Platform,_Standard_Editionhttp://en.wikipedia.org/wiki/Google_Earthhttp://en.wikipedia.org/wiki/Client_(computing)http://en.wikipedia.org/wiki/Server_(computing)http://en.wikipedia.org/wiki/Web_cachehttp://en.wikipedia.org/wiki/Java_Virtual_Machinehttp://en.wikipedia.org/wiki/Java_Virtual_Machinehttp://en.wikipedia.org/wiki/Plug-in_(computing)http://en.wikipedia.org/wiki/Web_browser


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the JAVA JRE installation, one can grant access to the local filesystem or system clipboard for

example, or to other network sources other than the network source that served the applet to the

browser.

Some applets require a specific JRE. This is discouraged.[31]

If an applet requires a newer JRE than available on the system, or a specific JRE, the user

running it the first time will need to wait for the large JRE download to complete.

Java automatic installation or update may fail if aproxy serveris used to access the web. This

makes applets with specific requirements impossible to run unless Java is manually updated. The

Java automatic updater that is part of a Java installation also may be complex to configure if it

must work through a proxy.

Unlike the olderapplet tag, the object tag needs workarounds to write a cross-browser HTML

document.

There is no standard to make the content of applets available to screen readers. Therefore,

applets can harm the accessibility of a web site to users with special needs.

Local & Remote Applets:

Local and Remote Applets

One of Java's major strengths is that you can use the language to create dynamic content for

your Web pages. That is, thanks to Java applets, your Web pages are no longer limited to the

tricks you can perform with HTML. Now your Web pages can do just about anything you

want them to. All you need to do is write the appropriate applets.

But writing Java applets is only half the story. How your Web page's users obtain and run the

applets is equally as important. It's up to you to not only write the applet (or use someone

else's applet), but also to provide users access to the applet. Basically, your Web pages can

contain two types of applets: local and remote. In this section, you learn the difference

between these applet types, which are named after the location at which they are stored.

Local Applets

A local applet is one that is stored on your own computer system (Figure 3.1). When your

Web page must find a local applet, it doesn't need to retrieve information from the Internet-in

fact, your browser doesn't even need to be connected to the Internet at that time. As you cansee in Listing 3.1, a local applet is specified by a path name and a file name.

Figure 3.1 :Local applets are stored on and loaded from your computer system.

Listing 3.1 LST3_1.TXT: Specifying a Local Applet.


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height=120>

In Listing 3.1, the codebase attribute specifies a path name on your system for the local

applet, whereas the code attribute specifies the name of the byte-code file that contains the

applet's code. The path specified in the codebase attribute is relative to the folder containing

the HTML document that references the applet. (See the "Optional Attributes for Applets"

section ofChapter 2for more information.)

Remote Applets

A remote applet is one that is located on another computer system (Figure 3.2). This

computer system may be located in the building next door or it may be on the other side of

the world-it makes no difference to your Java-compatible browser. No matter where theremote applet is located, it's downloaded onto your computer via the Internet. Your browser

must, of course, be connected to the Internet at the time it needs to display the remote applet.

Figure 3.2 :Remote applets are stored on another system and are down-loaded onto your

computer via the Internet.

To reference a remote applet in your Web page, you must know the applet's URL (where it's

located on the Web) and any attributes and parameters that you need to supply in order to

display the applet correctly. If you didn't write the applet, you'll need to find the document

that describes the applet's attributes and parameters. This document is usually written by the

applet's author. Listing 3.2 shows how to compose an HTML tag that accesses a

remote applet.

Listing 3.2 LST3_2.TXT: Specifiying a Remote Applet.

The only difference between Listing 3.1 and Listing 3.2 is the value of the codebase attribute.

In the first case, codebase specifies a local folder, and in the second case, it specifies the URL

at which the applet is located.
http://podgoretsky.com/ftp/Docs/Java/Java%20By%20Examples/ch2.htmhttp://podgoretsky.com/ftp/Docs/Java/Java%20By%20Examples/ch2.htmhttp://podgoretsky.com/ftp/Docs/Java/Java%20By%20Examples/ch2.htmhttp://podgoretsky.com/ftp/Docs/Java/Java%20By%20Examples/f3-2.gifhttp://podgoretsky.com/ftp/Docs/Java/Java%20By%20Examples/f3-2.gifhttp://podgoretsky.com/ftp/Docs/Java/Java%20By%20Examples/f3-2.gifhttp://podgoretsky.com/ftp/Docs/Java/Java%20By%20Examples/f3-2.gifhttp://podgoretsky.com/ftp/Docs/Java/Java%20By%20Examples/f3-2.gifhttp://podgoretsky.com/ftp/Docs/Java/Java%20By%20Examples/f3-2.gifhttp://podgoretsky.com/ftp/Docs/Java/Java%20By%20Examples/ch2.htm


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Applet & Application:

Applications, in short, are computer programs that you write that run on your

computer. You start from scratch, and you write the whole program; you have full

control. Applications start by you typing onto the screen java NameOfClass. TheJava software on your computer looks for the class that has the same name (in this

case NameOfClass), looks to see if it has a main method. If it does it starts from the

main method, and continues until either the program finishes, or is terminated by the

user (i.e., by pressing control C).

Applets on the other hand are programs that you write, and put inside your web

page. When someone opens up your web page, he automatically downloads any applet

that you have on your web page, just like an image. But by an applet, you can't always

control how much of the screen the applet takes up. The applet is shown with the web

page on the browser. Let's say that the user has an applet that is running on the

browser, and he opens up a different window over your applet. Your applet is going to

have to know how to stop in middle of what it is doing, and restart when the user goes

back to your applet. Let's say the user resizes the browser window, then your applet is

going to have to know how to redraw itself. That is a lot of work. The good news is

that you do not have to do the work. When you extend the Applet class (for now all

that means is you write extends applet after the name of the class), the browser does

most of the work for you. The browser supplies the "main" method, and around 200

methods that deal with the window resizing, starting, stopping, etc. The browser is

like a container that has its own Java machine, and all that it needs is for you to fill in

mainly two spots; what do you want the applet to do when it starts and downloads the

applet for the first time, and what do you want for the applet to do when it needs to

redraw itself every time. For example, let's say that your applet comes with an image

picture. You want to tell the browser to download the image only once, and save it

temporarily, while the user is on your site. However, you want the browser to redraw

the picture every time something blocks it. Therefore, there are two spots available,

one where you tell it that when the user starts the applet the first time download the

picture, and the second for when you want the applet to redraw the picture. If you told

it to download the picture every time it needed to be redrawn your applet would take

forever, and if you told it to draw the picture only once then if the user opened another

window on top of it and takes it off, your picture would not be redrawn. Therefore

there are two main spots to fill, and the browser does the rest of the work. Because the

browser runs its own Java software (which has to be this way, because the user might

not have any of its own Java software elsewhere), you have to follow the rules of the

browser that it is running on. Some browsers, especially the old ones, are unable to

run Swing (advanced graphics), and therefore if you care you would choose to use

only the simple graphics that all browsers use. See theDownloading Browserssection.

Another difference is that for security reasons applets are sometimes restricted in

creating it's own network connections, looking into your files, etc.

Or in other words
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Applets as previously described, are the small programs while applications are larger programs.

Applets don't have the main method while in an application execution starts with the main method.

Applets can run in our browser's window or in an appletviewer. To run the applet in an appletviewer

will be an advantage for debugging. Applets are designed for the client site programming purpose

while the applications don't have such type of criteria.

Applet are the powerful tools because it covers half of the java language picture. Java applets are the

best way of creating the programs in java. There are a less number of java programmers that have

the hands on experience on java applications. This is not the deficiency of java applications but the

global utilization of internet. It doesn't mean that the java applications don't have the place. Both

(Applets and the java applications) have the same importance at their own places. Applications are

also the platform independent as well as byte oriented just like the applets.

Applets are designed just for handling the client site problems. while the java applications are

designed to work with the client as well as server. Applications are designed to exists in a secure

area. while the applets are typically used.

Applications and applets have much of the similarity such as both have most of the same features

and share the same resources. Applets are created by extending the java.applet.Applet class while

the java applications start execution from the main method. Applications are not too small to embed

into a html page so that the user can view the application in your browser. On the other hand applet

have the accessibility criteria of the resources. The key feature is that while they have so many

differences but both can perform the same purpose.

Review of Java Applets: You have previously learned about the java applets. To create an applet

just create a class that extends the java.applet.Applet class and inherit all the features available in the

parent class. The following programs make all the things clear.

import java.awt.*;

import java.applet.*;

class Myclass extends Applet {

public voidinit() {

/* All the variables, methods and images initialize here

will be called only once because this method is called only

once when the applet is first initializes */

}

public voidstart() {

/* The components needed to be initialize more than once


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in your applet are written here or if the reader

switches back and forth in the applets. This method

can be called more than once.*/

}

public voidstop() {

/* This method is the counterpart to start(). The code,

used to stop the execution is written here*/

}

public voiddestroy() {

/* This method contains the code that result in to release

the resources to the applet before it is

finished. This method is called only once. */

}

public voidpaint(Graphics g) {

/* Write the code in this method to draw, write, or color

things on the applet pane are */

}

}

In the above applet you have seen that there are five methods. In which two ( init() and destroy ) are

called only once while remaining three (start() , stop() , and paint() ) can be called any number of

times as per the requirements. The major difference between the two (applet and application) is that

java applications are designed to work under the homogenous and more secure areas. On contrary to

that, java applets are designed to run the heterogeneous and probably unsecured environment.

Internet has imposed several restrictions on it.

Applets are not capable of reading and writing the user's file system. This means that the applet

neither can access nor place anything locally. To illustrate this lets take an example.. Many Window

based C applications uses the .INF file as the initialization file to store the information about the

application and any user preferences in 16-bit Windows or the Registry in 32-bit Windows. While in

case of current applet it is not possible.

One more thing to point here is that applets are unable to use the native methods, run any program

on the user system or load shared libraries. The major security concern here is that the local shared

libraries and the native methods may results in the loophole in the java security model.


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Applets are not capable of communicating the server than one from which they are originating. There

are the cases in which an encryption key is used for the verification purpose for a particular applet to

a server. But accessing a remote server is not possible.

The conclusion is that the java applets provides a wide variety of formats for program execution and a

very tight security model on the open environment as on the Internet.

Introduction to Java Application : Java applications have the majority of differences with the java

applets. If we talk at the source code level, then we don't extend any class of the standard java library

that means we are not restricted to use the already defined method or to override them for the

execution of the program. Instead we make set of classes that contains the various parts of the

program and attach the main method with these classes for the execution of the code written in these

classes. The following program illustrate the structure of the java application.

public class MyClass {/* Various methods and variable used by the classMyClass are written here */class myClass {/* This contains the body of the class myClass */}

public static voidmain(String args[]) {/* The application starts it's actual executionfrom this place. **/}

}

The main method here is nothing but the system method used to invoke the application. The code

that results an action should locate in the main method. Therefore this method is more than the other

method in any java application. If we don't specify the main method in our application, then on running

the application will through an exception like this one:

In the class MyClass: void main(String args[]) is undefined

But at higher level major concern is that in a typical java application security model, an application can

access the user's file system and can use native methods. On properly configuring the user's

environment and the java application it will allow access to all kind of stuff from the Internet.

In most of the cases it is seen that the java application seems like a typical C/C++ application. Now

we are going to create plenty of applications to exemplify some of the methods and features of a

specific Java application. All of them are console based Java applications because here we are not

going to cover the AWT.


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Applet Life Cycle:

When you run the Applet you will find that when an applet begins, the AWT calls the following

methods, in this sequence:-

1) Init()

2) Start()

3) Paint()

And, when an applet is terminated, the following sequence of method calls takes place:

1) Stop()

2) Destroy()

init() when the applet is first loaded, init()method is very first method to be called . It is calledexactly once in an applet's life. This is where we should initialize variables, read PARAM tags, start

dowloading any other images or media files or setup the user inerface. Many applets have init()

method but it is not compulsory to overide.

start() Start() method is called just after init() method. It is called at least once in an applet's life.start( ) is called each time an applets HTML document is displayed onscreen. So, if a user leaves a

web page and comes back, the applet resumes execution at start( ). Many applets have start()

method but it is not compulsory to overide.

paint()Applet needs to draw the AWT window for displaying output (strings and figures). For thispaint() method is called. The paint( ) method is called each time your applets output must be

redrawn. For example, the window in which the applet is running may be overwritten by another

window and then uncovered. Or the applet window may be minimized and then restored.The paint( ) method has one parameter of type Graphics. This parameter will contain the graphics
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context, which describes the graphics environment in which the applet is running. This context is

used whenever output to the applet is required.

stop() Stop() method is complement of start() method. The stop() method is called at least once in

an applet's life, when the browser leaves the page in which the applet is embedded.

destroy() The destroy() method is called exactly once in an applet's life, just before the browserunloads the applet. This frees up any resources the applet may be using. The stop( ) method is

always called before destroy( ). This method can be said as a complement of the init() method.

creating an executable applet :

Executable applet is nothing but the .class file of the applet, which is obtained by compiling thesource code of the applet. Compiling an applet is exactly the same as compiling an application.

Therefore, we can use the Java compiler to compile the applet.

Assume that we have created a file calledHelloJava.javafor our applet. Here are the steps

required for compiling theHelloJavaapplet.

1.Move to the directory containing the source code and type the following

command:javacHelloJava.java

2.The compiled output file calledHelloJava.classis placed in the same directory as the source.

3.If any error message is received, then we must check for errors, correct them and compile theapplet again.


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In Other words

These optional steps describe how to create an applet client that runs in a Webbrowser. Complete all steps under"Creating the application"before running the

applet:

1. Verify that your browser can run JDK 1.2 applets.2. Prepare your EAServer installation to run applets.3. Write the applet code.4. Create an HTML page to run the applet.5. Run the applet.

Applet Tag :

Applets are embedded in HTML documents with the tag.

The tag resembles the HTML image tag.[1] It contains attributesthat identify the applet to be displayed and, optionally, give the Web browser hints

about how it should be displayed. The standard image tag sizing and alignment

attributes, such as height and width, can be used inside the applet tag. Unlike

images, however, applets have both an opening and a

closing tag. Sandwiched between these can be any number

of tags that contain application-specific parameters to be passed to theapplet itself:

[1] If you are not familiar with HTML or other markup languages, you may wantto refer toHTML: The Definitive Guide, from O'Reilly & Associates, for a

complete reference on HTML and structured Web documents.

[][]...

3.4.1 Attributes

Attributes are name=value pairs that are interpreted by a Web browser

or appletviewer. (Many HTML tags besides have attributes.) Attributes of

the tag specify general features that apply to all applets, such as size and

alignment. The definition of the tag lists a fixed set of recognizedattributes; specifying an incorrect or nonexistent attribute should be considered anHTML error.
https://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp11.htmhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp11.htmhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp11.htmhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#CHDBEHAIhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#CHDBEHAIhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#CHDIGJDJhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#CHDIGJDJhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#X19451https://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#X19451https://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#X35933https://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#X35933https://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#CHDDFCCBhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#CHDDFCCBhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#CHDDFCCBhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#X35933https://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#X19451https://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#CHDIGJDJhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp12.htm#CHDBEHAIhttps://awebproxyprd.ins.state.ny.us/docs/jaggs/cookp11.htm


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Three attributes are required in the tag. Two of these attributes specifythe space the applet occupies on the screen: not surprisingly, they're

named width and height. The third required attribute may be either code or object;you must supply one of these attributes, and you can't specify both.

The code attribute specifies the class file from which the applet is loaded;the object attribute specifies a serialized representation of an applet. Most often,

you'll use the code attribute; the tools for creating serialized applets aren't quite

there yet. (Serializing an applet, or any Java class, means saving it, perhaps aftercustomizing it, for use later. You can use appletviewerto create serialized applets,

but that feature isn't really useful yet. Serialized applets will become interestingwhen the next generation of integrated development environments for Java are

available.)

The following is an HTML fragment for a hypothetical, simple clock applet that

takes no parameters and requires no special HTML layout:

The HTML file that contains this tag must be stored in the same directory

as the AnalogClock.class class file. The applet tag is not sensitive to spacing, sothe above is therefore equivalent to:

You can use whatever form seems appropriate.

3.4.2 Parameters

Parameters are analogous to command-line arguments; they provide a way to pass

information to an applet. Each tag contains a name and a value that arepassed as strings to the applet:

Parameters provide a means of embedding application-specific data and

configuration information within an HTML document.[2] Our AnalogClock applet,for example, might accept a parameter that selects between local and universal

time:

[2] If you are wondering why the applet's parameters are specified in yet another

type of tag, here's the reason. In the original alpha release of Java, applet

parameters were included inside of a single tag along with formatting


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attributes. However, this format was not SGML-compliant, so the tag wasadded.

Presumably, this AnalogClock applet is designed to look for a parameter

named zone with a possible value ofGMT.

Parameter names and values can be quoted to contain spaces and other special

characters. We could therefore be more verbose and use a parameter value like thefollowing:

The parameters a given applet expects are determined by the developer of that

applet. There is no fixed set of parameter names or values; it's up to the applet tointerpret the parameter name/value pairs that are passed to it. Any number of

parameters can be specified, and the applet may choose to use or ignore them as itsees fit. The applet might also consider parameters to be either optional or required

and act accordingly.

i/o Basics:I/O Fundamentals

The Java language provides a simple model for input and output (I/O). All I/O is

performed by writing to and reading from streams of data. The data may exist in a

file or an array, be piped from another stream, or even come from a port on

another computer. The flexibility of this model makes it a powerful abstraction of

any required input and output.

One of the key issues regarding Java I/O is providing file support for all Javaenabled

platforms. The Java file I/O classes must restrict themselves to a

reasonable, "least common denominator" of file-system functionality. Provided

functionality is restricted to only those general features that can be used on anymodern platform. For example, you won't find ways to work with OS/2's

"extended attributes", or "sync" a file in UNIX.

All classes referred to in this module are located in the java.io package (unless

otherwise stated.)

Notes

A few notes on the content and examples in this module:

This module refers to some methods and classes that are only available in the

Java 2 SDK, standard edition v1.2 (formerly known as "JDK 1.2"). Methods

and classes such as these are marked "(since 1.2)"

We discuss the most commonly used methods in these classes, not necessarily

all available methods. See the javadocs for a list of all methods in each class.

All examples will require exception handling to catch IOException. This


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exception handling is omitted in many examples for clarity, and discussed at

the end of the module. If an example is a complete class listing, the exception

handling will be present.

UNIT IV

String handeling:

A String is a sequence of characters. In many other languages a string is treated as acharacter array. But in Java a string is treated as an object. After creating a string object

you can not change it. So that is why it is said that a string is immutable. Java providesthree string classes named String, StringBuffer and StringBuilder. The reason for threeclass is to reduce the problem of the mutability of

the StringBuffer and StringBuilder classes; both are mutable. But in your mind youmight ask why not remove the String class. The reason is that an immutable

String can be implemented more efficiently. The StringBuffer and StringBuilder classeshave the same methods with one difference and that's synchronization. A StringBuffer issynchronized (which means it is thread safe and hence you can use it when youimplement threads for your methods) whereas StringBuilder is not synchronized (which

implies it isn't thread safe). So, if you aren't going to use threading then usethe StringBuilder class as it wll be more efficient than StringBuffer due tothe absence ofsynchronization.In this article we describe the String class and its methods.

String class

The String class has several constructors (near about 13) and several methods (nearabout more than 60) so it's not possible to describe all of them but the importantconstructors and methods are described in this article.

Constructor summary

String()Initializes a newly created String object so that it represents an empty character

sequence.

String(Charchars[])

Allocates a new String so that it represents the sequence of characters currentlycontained in the character array argument.

String(String

strobj)

Initializes a newly created String object so that it represents the same sequence ofcharacters as the argument; in other words, the newly created string is a copy of the

argument string.String(byte[]bytes)

Constructs a new String by decoding the specified array of bytes using the platform'sdefault charset.

Method Summary

ReturnType

Name Description

char charAt(int index) Returns the char value at the specified index.

int

compareTo(String

anotherString) Compares two strings lexicographically.

int compareToIgnoreCase( String Compares two strings lexicographically, ignoring case


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str) differences.

String concat(String str) Concatenates the specified string to the end of this string.

int indexOf(int ch)Returns the index within this string of the first occurrence of thespecified character

stringreplace(char oldchar, char

newchar)

Returns a new string resulting from replacing all occurrences

ofoldChar in this string with newChar.int length() Returns the length of this string.

char[] toCharArray() Converts this string to a new character array.

String trim()Returns a copy of the string, with leading and trailingwhitespace omitted.

StaticString

valueOf(Object obj) Returns the string representation of the Object argument.

Other words

The String class is defined in thejava .lang package and hence is implicitly available to

all the programs in Java. The String class is declared as final, which means that it cannot

be subclassed. It extends the Object class and implements the Serializable, Comparable,

and CharSequence interfaces.

Java implements strings as objects of type String. A string is a sequence of characters.

Unlike most of the other languages, Java treats a string as a single value rather than as

an array of characters.

The String objects are immutable, i.e., once an object of the String class is created, thestring it contains cannot be changed. In other words, once a String object is created, the

characters that comprise the string cannot be changed. Whenever any operation is

performed on a String object, a new String object will be created while the original

contents of the object will remain unchanged. However, at any time, a variable declared

as a String reference can be changed to point to some other String object.

Other words

String represents a sequence of characters. It has fixed length of character sequence. Once a

string object has been created than we can't change the character that comprise that string. It is

immutable. This allows String to be shared. String object can be instantiated like any other object

String s=new String();

This creates an empty string by calling default constructor.

char c[]={'a','b','d'};

String s=new String(c);
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In this case string s points to the character array "abd".

StringBuffer

This represents growable and writeable character sequence. It is mutable in nature. StringBuffer

are safe to be used by multiple thread as they are sunchronized but this brings performance

penalty. It defines 3-constructor:

StringBuffer(); //initial capacity of 16 characters

StringBuffer(int size); //The initial size

StringBuffer(String str);

The following table describes the various important string search methods.

int indexOf(int ch) Returns the first occurrence of the specified character.

int lastIndexOf(int ch) Returns last occurrence of the specified character.

boolean contains(CharSequence s) Returns true if the string contains the specified character sequence.

String replace(char oldChar,char

newChar)

Returns a new string resulting from replacing all occurrences of oldChar in t

string with newChar.

String substring(int startIndex)return a subtring,and startindex specifies the index at which substring will

begin.

String trim() This will removed the leading and trailing whitespace

String concat(String str) It will append the string str at the end.

StringBuilder

StringBuilder class is introduced in Java 5.0 version. This class is an alternative to the existing

StringBuffer class. If you look into the operations of the both the classes, there is no difference.

The only difference between StringBuilder and StringBuffer is that StringBuilder class is not

synchronized so it gives better performance. Whenever there are no threading issues, its


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preferable to use StringBuilder. StringBuffer class can be replaced by StringBuilder with a simple

search and replace with no compilation issue.

Event handeling:

No matter what theprogramming languageorparadigmyou are using, chances are that you will

eventually run into a situation where your program will have to wait for an external event to happen.

Perhaps your program must wait for some user input, or perhaps it must wait for data to be delivered

over the network. Or perhaps something else. In any case, the program must wait for something to

happen that is beyond the program's control: the program cannot makethat event happen.

In this situation there are two general options for making a program wait for an external event to

happen. The first of these is called pollingand means you write a little loop of the for "while the event

has not happened, check again". Polling is very simple to build and very straightforward. But it is also

very wasteful: it means a program takes up processor time in order to do absolutely nothing but wait.

This is usually considered too much of a drawback for programs that have to do a lot of waiting.Programs that have a lot of waiting moments (for example, programs that have a graphical user

interface and often have to wait for long periods of time until the user does something) usually fare

much better when they use the other mechanism: event-driven programming.

In event-driven programming a program that must wait, simply goes to sleep. It no longer takes up

processor time, might even be unloaded from memory and generally leaves the computer available to

do useful things. But the program doesn't completely go away; instead, it makes a deal with the

computer or theoperating system. A deal sort of like this:

Okay Mr. Operating System, since I have to wait for an event to happen,

I'll go away and let you

do useful work in the meantime. But in return, you have to let me know when

my event

has happened and let me come back to deal with it.

Event-driven programming usually has a pretty large impact on the design of a program. Usually, a

program has to be broken up into separate pieces to do event-drive programming (one piece for

general processing and one or more others to deal with events that occur). Event-driven programming

in Java is more complicated than non-event driven but it makes far more efficient use of the hardware

and sometimes (like when developing a graphical user interface) dividing your code up into event-

driven blocks actually fits very naturally with your program's structure.

In this module we examine the basis of the Java Platform's facilities for event-driven programming

and we look at some typical examples of how that basis has been used throughout the platform.

[edit]The Java Platform Event Model

[edit]Introduction

One of the most interesting things about support for event-driven programming on the Java platform is

that there is none, as such. Or, depending on your point of view, there are many different individual

pieces of the platform that offer their own support for event-driven programming.
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The reason that the Java platform doesn't offer one general implementation of event-driven

programming is linked to the origins of the support that the platform does offer. Back in 1996 the Java

programming language was just getting started in the world and was still trying to gain a foothold and

conquer a place for itself in software development. Part of this early development concentrated on

software development tooling likeIDEs. One of the trends in software development around that time

was for reusable software components geared towards user interfaces: components that would

encapsulate some sort of interesting, reusable functionality into a single package that could be

handled as a single entity rather than as a loose collection of individual classes. Sun Microsystems

tried to get on the component bandwagon by introducing what they called aJavaBean, a software

component not only geared towards the UI but that could also be configured easily from an IDE. In

order to make this happen Sun came up with a large specification of JavaBeans (the JavaBeans

Spec) dealing mostly with naming conventions (to make the components easy to handle from an IDE).

But Sun also realized at the same time that a UI-centric component would need support for an event-

driven way of connecting events in the component to business logic that would have to be written by

the individual developer. So the JavaBeans Spec also included a small specification for an event

Model for the Java platform.

When they started working on this Event Model, the Sun engineers were faced with a choice: try to

come up with a huge specification to encompass all possible uses of an event model, or just specify

an abstract, generic framework that could be expanded for individual use in specific situations. They

chose the latter option and so, love it or hate it, the Java Platform has no generic support for event-

driven programming other than this general Event Model framework.

Java Event HandlingBy S. Nageswara Rao, Corporate Traineron May 22, 2011

In AWT components, we came to know every component (exceptPanelandLabel)

generates events when interacted by the user like clicking over a button or pressing

enter key etc. Listeners handle the events. Let us know the style (or design pattern)

Java follows to handle the events.

The event handling involves four types of classes.

1. Event Sources

2. Event classes

3. Event Listeners

4. Event Adapters

1. Event Sources
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Event sources are components, subclasses ofjava.awt.Component, capable to

generate events. The event source can be a button, TextField or a Frame etc.

2. Event classes

Almost every event source generates an event and is named by some Java class. For

example, the button generatesActionEvent and Checkbox generates ItemEvent.

All events listed injava.awt.event package. Following list gives a few components

and their listeners.

Component Event it generates

Button, TextField, List, Menu ActionEvent

Frame WindowEvent

Checkbox, Choice, List ItemEvent

Scrollbar AdjustmentEvent

Mouse (hardware) MouseEvent

Keyboard (hardware) KeyEvent

The events generated by hardware components (like MouseEvent and KeyEvent)are known as low-level events and the events generated by software components

(like Button, List) are known as semantic events.

3. Event Listeners

The events generated by the GUI components are handled by a special group of

classes known as "listeners". Listener is an interface. Every component has its own

listener, say, AdjustmentListener handles the events of scrollbar Some listeners

handle the events of a few components. For example, ActionListener handles the

events of Button, TextField, List and Menus. Listeners are fromjava.awt.eventpackage.

More description on listeners and list of listeners is available atJava AWT

Listeners.

4. Event Adapters

When a listener includes many abstract methods to override, the coding becomes

heavy to the programmer. For example, to close the frame, you override seven

abstract methods of WindowListener, in which, infact you are using only one

method. To avoid this heavy coding, the designers come with another group ofclasses known as "adapters". Adapters are abstract classes defined
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injava.awt.event package. Every listener that has more than one abstract method

has got a corresponding adapter class.

AWT : working with windows grphics and text:

The Abstract Window Toolkit (AWT) was introduced inChapter 19because itprovidessupport for applets. This chapter begins its in-depth examination. The AWT

containsnumerous classes and methods that allow you to create and manage windows. A

fulldescription of the AWT would easily fill an entire book. Therefore, it is not possible

todescribe in detail every method, instance variable, or class contained in the AWT.However,

this and the following two chapters explain all the techniques needed toeffectively use the

AWT when creating your own applets or stand-alone programs. Fromthere, you will be able

to explore other parts of the AWT on your own.

In this chapter, you will learn how to create and manage windows, manage fonts, outputtext,and utilize graphics.Chapter 22describes the various controls, such as scroll barsand push

buttons, supported by the AWT. It also explains further aspects of Java's event-handling

mechanism.Chapter 23examines the AWT's imaging subsystem andanimation.

Although the main purpose of the AWT is to support applet windows, it can also be usedto

create stand-alone windows that run in a GUI environment, such as Windows. Most of theexamples are contained in applets, so to run them, you need to use an applet viewer or a Java-

compatible Web browser. A few examples will demonstrate the creation of stand-

alone, windowed programs

The AWT classes are contained in the java.awt package. It is one of Java's

largestpackages. Fortunately, because it is logically organized in a top-down,

hierarchicalfashion, it is easier to understand and use than you might at first

believe.

Although the basic structure of the AWT has been the same since Java

1.0, some of theoriginal methods were deprecated and replaced by new ones

when Java 1.1 wasreleased. For backward-compatibility, Java 2 still supports all

the original 1.0 methods.However, because these methods are not for use

with new code, this book does notdescribe them.


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Window Fundamentals

The AWT defines windows according to a class hierarchy that addsfunctionality andspecificity with each level. The two most common windows

are those derived from

Panel

,which is used by applets, and those derived from

Frame

, which creates a standardwindow. Much of the functionality of these windows

is derived from their parent classes.Thus, a description of the class hierarchies

relating to these two classes is fundamentalto their understanding. Figure 21-1

shows the class hierarchy for

Panel

and

Frame

. Let'slook at each of these classes now.

Component

At the top of the AWT hierarchy is the Component class.Component is an

abstractclass that encapsulates all of the attributes of a visual component. All

user interfaceelements that are displayed on the screen and that interact with the

user are subclasses of Component. It defines over a hundred public methods

that are responsible for managing events, such as mouse and keyboard input,

positioning and sizing the window,and repainting. (You already used many of

these methods when you created applets inChapters 19and20.) A Component

object is responsible for remembering the currentforeground and background

colors and the currently selected text font.


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Figure 21.1:

the class hierarchy for Panel and FrameContainer

TheContainer

class is asubclass ofComponent. It has additional methods that allowother Component

objects to be nested within it. Other Container objects can be storedinside of a

Container (since they are themselves instances ofComponent). This makesfor

a multileveled containment system. A container is responsible for laying

out (that is,positioning) any components that it contains. It does this through the

use of variouslayout managers, which you will learn about inChapter 22.

Panel The Panel class is a concrete subclass ofContainer . It doesn't add any

new methods; itsimply implements Container . APanelmay be thought of as a

recursively nestable,concrete screen component. Panel is the superclass

for Applet. When screen output isdirected to an applet, it is drawn on the

surface of a Panel object. In essence, a Panel isa window that does not contain

a title bar, menu bar, or border. This is why you don't seethese items when an

applet is run inside a browser. When you run an applet using anapplet viewer,

the applet viewer provides the title and border. Other components can be addedto a Panel object by its add( ) method (inherited from Container). Once these

components have been added, you can position and resize themmanually using

the setLocation( ),setSize( ), or setBounds( )methods defined by Component

.

Window TheWindow class creates a top-level window. A top-level window is

not contained withinany other object; it sits directly on the desktop. Generally,

you won't create Window objects directly. Instead, you will use a subclassofWindowcalled Frame, describednext.

Frame

Frame encapsulates what is commonly thought of as a "window." It is a

subclass of Window and has a title bar, menu bar, borders, and resizing

corners. If you create a Frame object from within an applet, it will contain a

warning message, such as "Warning:Applet Window," to the user that an applet

window has been created. This messagewarns users that the window they see


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was started by an applet and not by softwarerunning on their computer.

(An applet that could masquerade as a host-based applicationcould be used to

obtain passwords and other sensitive information without the user'sknowledge.)

When a Frame window is created by a program rather than an applet, anormal

window is created.

Canvas

- 471 -

Although it is not part of the hierarchy for applet or frame windows, there is one

other typeof window that you will find valuable:

Canvas.

Canvas encapsulates a blank window uponwhich you can draw. You will see an

example ofCanvas later in this book


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CONTROLS

WebLogic Workshop provides Java controls that make it easy for you to encapsulate

business logic and to access enterprise resources such as databases, legacy applications,and web services. There are three different types of Java Controls: built-in Java controls,

portal controls, and custom Java controls.

Built-in controls provide easy access to enterprise resources. For example, the Database

control makes it easy to connect to a database and perform operations on the data usingsimple SQL statements, whereas the EJB control enables you to easily access an EJB.Built-in controls provide simple properties and methods for customizing their behavior,and in many cases you can add methods and callbacks to further customize the control.

A portal control is a kind of built-in Java control specific to the portal environment. If you

are building a portal, you can use portal controls to expose tracking and personalizationfunctions in multi-page portlets.

You can also build your own custom Java control from scratch. Custom Java controls areespecially powerful when used to encapsulate business logic in reusable components. It

can act as the nerve center of a piece of functionality, implementing the desired overallbehavior and delegating subtasks to built-in Java controls (and/or other custom Javacontrols). This use of a custom Java control ensures modularity and encapsulation. Webservices, JSP pages, or other custom Java controls can simply use the custom Java

control to obtain the desired functionality, and changes that may become necessary canbe implemented in one software component instead of many.

If you are connecting to an enterprise resource that exposes a standards-based, J2EE, orWeb Services interface, you can create a custom Java control to directly connect to thatapplication. However, if you are connecting to an external resource that is proprietary or

does not expose standard J2EE APIs, you may need to use a JCA (Java ConnectorArchitecture) adaptor and an Application View control rather than a Java control toconnect to that resource. JCA adaptors and the Application View control are available

through WebLogic Integration. For more information on using JCA adaptors and theApplication View control, seeOverview: Application Integration.

LAYOUT MANAGERS

Layout Managers in JavaTM technology

Basics of Layout Managers

Java technology uses Layout Managers to define the location and size of

Graphical User Interface components. Java technology does not encourage

programmers to use absolute location and size of components. Java

technology instead places components based on specified Layout Manager.

A Layout Manager implements a layout policy that defines constraints

between components in a container.
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Types of Layout Managers

Java technology provides the following Layout Managers, each of which

implements the LayoutManager interface.

FlowLayout

GridLayout

BorderLayout

GridBagLayout

CardLayout

The FlowLayout is the default Layout Manager for Panel, and hence the

Applet class. The BorderLayout is the default Layout Manager for Windowclass and its subclasses (Frame and Dialog).

Setting Layout Managers

The following method defined in the Container class can be used for setting

layout managers.void setLayout(LayoutManager mgr);

So for example to set FlowLayout as the Layout Manager for a container C,

the following can be used -

C.setLayout(new FlowLayout());

The add method defined in the Container class can be used for adding

components to a container. The following are the prototypes of the add

method -Component add(Component comp);

Component add(Component comp, int index);

void add(Component comp, Object constraints, int index);

void add(Component comp, Object constraint);

The order in which components are added to a container effects the

placement of components. Also a component added to a container canitself be a container that holds other components.

FlowLayout Manager

FlowLayout places component in rows from left to right. Components

towards the end of row are written on next row, if there is not enough

space in the current row. The FlowLayout honors the specified size of a

component. The size of a component never changes regardless of size of

container. The following constructors of FlowLayout are provided by AWT -FlowLayout();


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FlowLayout(int alignment);

FlowLayout(int alignment, int hor_gap, int ver_gap);

Alignment can take values of constants - LEFT, CENTER and RIGHT. The

default alignment for the components in a row is center. Default horizontaland vertical gaps are 5 pixels.

GridLayout Manager

A GridLayout Manager places the components in a rectangular grid. Each

component's position is identified by a column and row. All the cells in the

grid have same size and width. Each component is stretched to the cell size.

So a GridLayout ignores the Component's preferred size.

The GridLayout class provides the following constructors.GridLayout();GridLayout(int rows, int columns);GridLayout(int rows, int columns, int hor_gap, int ver_gap);

This creates a row*col grid layout with the specified horizontal and vertical

gaps. In the constructor, either rows or cols can be zero, but not both. The

first constructor is equivalent to one row with any number of components.The default gap between components is zero pixels.

BorderLayout Manager

A BorderLayout Manager divides the window into five regions - North, East,

West, South and Center. A component can be explicitly added to one of the

regions using the add() method of the Container class. Any space left over

by the component in North, East, South and West is occupied by the

component in Center. Only the last component added to a region is shown,

and not all regions need to be occupied by a component. So a container

that uses BorderLayout may have up-to 5 components.

The BorderLayout class defines the following constructors -BorderLayout();BorderLayout(int hor_gap, int ver_gap);

As illustrated below, components can be added to the container using add()

method defined in the Container class.Component add(Component comp);void add(Component comp, Object constraints);

Here constraints can be NORTH, SOUTH, EAST, WEST and CENTER.

These constants correspond to strings "North", "South", East", "West", and


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"Center" respectively. They describe the region where the component shouldbe placed. The default region is CENTER.

GridBagLayout

GridBagLayout is the most advanced LayoutManager in Java technology.

Refer toThe Java AWT: GridBagLayoutfor an excellent coverage of

GridBagLayout. Typically the Certification exam includes one question on

GridBagLayout.
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Documents

Unit III- IV Java