Chapter 2© copyright Janson Industries 20141 Java ▮ Java/PC programming environment ▮ Java syntax rules ▮ Java documentation ▮ Java/RAD coding example

Chapter 2 © copyright Janson Industries 2014 1

Java

▮ Java/PC programming environment

▮ Java syntax rules

▮ Java documentation

▮ Java/RAD coding example

This presentation is stored in 4thed.Ch02.ppt

Non-graded assg


Setting up the environment

▮ Files are identified by a name, myfile.doc, and location (aka path), C:\Program Files\

▮ When a file is identified by the path and file name, C:\Program Files\myfile.doc, it is considered a fully-qualified reference

▮ If a file is referred to with only name, myfile.doc, it is a non-qualified reference



▮ Having to type the fully-qualified name of every file is time consuming and error prone

▮ The PATH system variable tells Windows where to search for non-qualified file references

▮ The CLASSPATH indictates where to search for non-qualified .class file references



▮ Defining Path and CLASSPATH every time is time consuming

▮ Could create a .bat program called init

▮ Init.bat would contain the commands to define Path and CLASSPATH

▮ Simply run init each time

▮ Or, define the system variables permanently


Setting the Path

Right click:

“Computer”

Choose:

Properties

Click:

Advanced system settings

Click:

Environment Variables button


In the System Variables pane:

Click the variable Path

Then the Edit button

Setting the Path


In the Edit System Variable

window, add to the end of the

Path value:

;c:\jdk\bin

Then Click the OK button

Change CLASSPATH by

adding the path of your

java application (i.e. .class

files) to the variable

;c:\

Setting the Path (Windows 7)


Setting the Classpath

▮ If there is no classpath environment variable, create one

▮ Click New and specify the variable name (classpath) and value


General steps to run on PC▮ Save the source code (E.g. Customer.java)

▮ Bring up the command prompt

▮ Set path (path=f:\jdk\bin) to identify the loaction of the javac and java commands

▮ Set classpath (Set classpath=.;f:\) to identify location of java class files (i.e. .class files)

▮ Or, change the environment values

▮ Convert to byte code (javac Customer.java)

▮ Run the program (java Customer)


Java Concepts

▮ Java “program” is called a class

▮ Java classes grouped into projects and packages

▮ Java classes comprised of global/class variable definitions and methods

▮ Methods contain executable statements and local/method variable definitions

▮ Are you familiar with what variables do?


Java Language Organization

Project

Package Package Package

Class Class Class

Variable Method Method Method Variable

Variable Statement Statement


Java Language Concepts

▮ Let’s concentrate on the source code

▮ Java classes comprised of class (global) variable definitions and methods

▮ Methods contain executable statements and method (local) variable definitions


Classes

Class

Variable Variable Method Method Method

Variable Statement Statement Class comprised of class variable definitions and methods

Methods contain method variable definitions and executable statements


Java Class Example// Customer.java

public class Customer {

String custName, custStreet, custCSZ;

public Customer() { custName = "No Name";

custStreet = "No Street";

custCSZ = "No CityStateZip"; }

public void printCustInfo(){

System.out.println("CUSTOMER NAME IS: " + custName);

System.out.println("CUSTOMER STREET IS: " + custStreet);

System.out.println("CUSTOMER CSZ IS: " + custCSZ); }

public static void main( String[] args ) {

Customer aCust = new Customer();

aCust.custName = "Joe Customer";

aCust.printCustInfo();

}

}

methods

Class variables

statements

Method variable


Classes

▮ Divided into the header and the body

▮ Header defines:▮ The source code as a class (e.g. “class”)▮ Access allowed (e.g. “private”, “public”)▮ The name of class

▮ Must begin with an upper case letter▮ Must match .java file name

▮ Body is enclosed in braces and contains class variables and methods

▮ Simple class header example:▮ public class Customer { BODY }

Class namesAre case sensitive!Begin with a capital letterNo spaces

Body of class begins and ends with bracesChapter 2 © copyright Janson Industries 2014 16

Class Definition:Header

Body public class Customer {

class variables

method{}

method{}

}

Java Class

Class access Class name

“A class contains a template for creating objects”


Java Method

▮ Comprised of a header/definition and body

▮ Header/definition comprised of:▮ Modifiers (e.g. private, public, static)

▮ Return value type (e.g. void, String)

▮ Method name begins with a lower case letter (e.g. “getMailingLabel”, “main”)

▮ Parameter(s)/received value(s) in parenthesis (e.g. (String name), (int age), () means no params)

18

Java Method

▮ When a parameter is define must specify the data type and the variable name to hold the data

▮ So with (String name) String is the data type and the variable that will hold the passed value is name

▮ (int age), data type is integer (int) and the variable name is age


Java Method

▮ Method header/definition examples:

▮ public void setCustomerName(String custName)

▮ public String getMailingLabel()

▮ public static void main(String[ ] args)

▮ public void setTaxRate(double taxRate)


Java Method

▮ Method "access" modifiers (cont’d):

▮ Private methods:▮ only accessed by other methods within the

class

▮ Public methods:▮ can be accessed by objects external to the

class▮ comprise the class “interface”

▮ Variables can also be public or private ▮ public can be accessed by objects external

to the class


Java Concepts

▮ Java classes can be invoked many ways

▮ 2 primary ways

▮ Run with the java command

▮ Instantiated▮ An object (aka an instance) of the class type is

created

▮ An object is an "instance of a class" and is usually associated with a variable


Java Concepts

▮ If java class is invoked with the java command:▮ main method bytecode converted to machine

language▮ main method machine language loaded into

main memory▮ main method is executed

▮ If Java class is instantiated:▮ Entire class' bytecode converted to machine

language and loaded into main memory▮ i.e. An object of that class type is created

▮ Class (global) variables created▮ constructor method is executed


Specialized Methods

▮ Constructors are methods that:▮ Can not return any values▮ Have the same name as the class▮ Are run when the object is instantiated▮ Are used to initialize variables and perform setup

operations (e.g. open files, assign user supplied values, establish communication links, etc.)

▮ Static method “main”:▮ Java command invokes main method in

applications (main is not run when object instantiated)

▮ Main method header must be defined precisely as follows:


public static void main(String[ ] args)

main Method

No values returned

Any class can use

The method expects an array of String variables (called args)

When main is invoked, object not created

Method name


Notice how much the class and constructor method headers look alike

What's the difference?

Customer has a class header, constructor, and main method that follow the previously defined rules


Method body

▮ Comprised of:▮ variable definitions▮ executable statements

▮ Enclosed in braces { } public Customer(String name, String street, String cityStateZip)

{

private String custName = null;

private String custStreet = null;

private String custCityStateZip = null;

custName = name;

custStreet = street;

custCityStateZip = cityStateZip;

}


Java Language

▮ Variables usually defined at the beginning of a class or method

▮ Variable definitions:Access modifier (e.g. “private”, “public”) (optional)Data type (e.g. “int”, “String”)Name (e.g. “custID”, “custName”)Initial value (optional)End with a semicolon (;)

▮ Examples:private int custID = 0;public String custName = null;


Java Language

Multiple line comment

Single line comment

Multiple line comment

▮ Comment examples:

/* This is an example */

/** This is an example */

public int custID = 0; // This is an example

▮ In RAD, comment out and uncomment any line(s) by selecting and pressing CTRL + /


Programming Conventions

▮ Class header and start of body defined

public class Customer {

▮ Class variables defined private String custCityStateZip = null;

private static int lastCustID = 100000;

▮ Methods defined public Customer(String cityStateZip) {

custCityStateZip = cityStateZip;int custID = lastCustID + 1;

}

▮ Class body ended }


Source Code Rules

▮ Statements end with a semicolon (;)private String custCityStateZip = null;private static int lastCustID = 100000;

▮ Very forgiving re: extra spaces and linesprivate String custCityStateZip = null ;

public Customer(String cityStateZip) { custCityStateZip = cityStateZip; int custID = lastCustID + 1; }

▮ To invoke a class method from another class method (and pass many parms):

this.methodName(parm, parm, etc); returnValue = this.methodName(parm, parm, etc.);


Source Code Rules

▮ To invoke a method from outside the class, instantiate an object of the class type, create a variable of the class type and assign the object to the variable :

▮

Syntax: ClassName variableName = new ClassName(); Example: Customer myCust = new Customer();

▮ Then invoke the object’s method:Syntax: variableName.methodName();

Example: myCust.printCustInfo();


Source Code Rules

▮ Weird? Not really. To use Word Processing commands, don’t you need to create a document?

▮ To use queue commands, doesn’t a queue have to be created (and referenced in each command)?

▮ So why shouldn’t you have to create a Customer object to use a customer function?

Customer myCust = new Customer();

myCust.printCustInfo();


Class header

Class variables

Method headerStatements

Method header

Statements

Method headerStatements

What will be the result of running Customerc2sl31 as an application?


Execution Results▮ main method bytecode converted to machine

language and loaded into main memory

▮ First statement in main executed: a Customer object is created. This means:▮ The entire Customer class’ bytecode is converted to

machine language and loaded into main memory

▮ 3 String objects are created, 3 String class level variables (custName, custStreet and custCSZ) are created, and the String objects are assigned to the variables

▮ The Customer object’s constructor is executed. This means:


Execution Results▮ 3 String objects are created with the text “No Name”, “No

Street”, “No CityStateZip”▮ 3 new String objects are assigned to the variables custName,

custStreet and custCSZ

▮ Execution returns to the first statement in the main method and▮ The Customer variable aCust is created▮ The Customer object is assigned to aCust

▮ Second statement in main executed:▮ A String object is created with the text “Joe Customer”▮ The new String object with the value “Joe Customer” is assigned

to the Customer object’s class level String variable custName


Execution Results

▮ Third statement in main executed: the Customer object’s printCustInfo method invoked. This means:

▮ First println statement is executed, what is shown?

▮ Second println statement is executed, what is shown?

▮ Third println statement is executed, what is shown?


What will be the result of running this?Let’s create a new class and run…

Proving main vs. constructor

Chapter 2 © copyright Janson Industries 2014 38Click on the src folder name and then File, New, Class


Specify the name of the new class (Cust1), click Finish


Starts you with a frameworkMove the cursor and start typing


Enter the source code and run What are the results and why?


Exporting: Moving an app from RAD to the production environmentClick FILE then EXPORT


Click File system then Next


In real world, usually export to JAR (Java ARchive) files.

They are compressed files.


1. Select the java files to

export

...click browse and specify the

location

2. Enter export destination or...

3. Click OK

4. Click Finish

Chapter 2 © copyright Janson Industries 2014 46Click Finish

Notice options to create directories and overwriting files


Go out and verify Cust1.java is there.


Open with notepad to display


javac and java

Make sure classpath and path variables are set


Exporting

▮ Moving between/setting up environments is one the most difficult thing (conceptually) for new programmers

▮ Programmers develop apps within an IDE (like RAD) and export to the production environment


Exporting

▮ This is where packages can mess you up!

▮ Ex. For a Customer class stored in project Proj1 and package C1:

▮ Customer must have a package statement at beginning of class

package C1;

▮ Class name is now considered C1.Customer


Exporting and Running

▮ When file exported to Windows, Customer file must be in a directory/folder called C1

▮ Project and packages (except default pkg) implemented in Windows as directories

▮ So, if "create directory structure" specified▮Both Proj1 and C1 directories are created▮Also a src folder is created

▮ javac Customer will fail because Customer not class name ▮ javac C1/Customer will fail because Proj1 not in classpath



▮ Need to add Proj1 to the classpath and refer to the class with package name included in the class name

▮ Set classpath = f:\Proj1\src

▮ javac C1/Customer

▮ Be careful of directory structure when exporting!

▮ I suggest just exporting the package as a directory


▮ In other words, on the export window choose the third option "create only selected directories"

▮ Then click the java file and the package's checkboxes

▮ I.e. select the package/directory

▮ This will result in a folder with the package name and the java file inside it



▮ No project folder or src folder will be created

▮ You wont have to add them to the path

▮ Still need to set the path to the location of the package/folder though

▮ Then issue javac command with the package/folder name and the java file name



Non - Graded Assgs

▮ Export file(s) or package (recommended) out of RAD workspace as a jar file

▮ Source and .class files

▮ Send the jar file as an email attachment to [email protected]

▮ I will acknowledge receiving them within one business day

▮ If you do not hear from me, I did not receive them


Non - Graded Assgs

▮ How to check you exported a jar file correctly

▮ Create a new project

▮ Import the jar into the project by▮ Choosing Import archive file▮ Specify the jar file

▮ Expand the project and confirm that all the packages and source code files are there


Graded Assgs

▮ Export package(s) or entire project(s) out of RAD workspace as a jar file

▮ Source and .class files

▮ Send the file(s) as an email attachment to [email protected]

▮ I will acknowledge receiving them within one business day

▮ If you do not hear from me, I did not receive them


Graded Assgs

▮ How to check you exported the jar correctly

▮ Create a new project

▮ Import the jar into the project by▮ Choosing Import archive file▮ Specify the jar file

▮ Expand the project and confirm that all the packages and source code files are there


Documentation

▮ Online documentation available. Ex:

▮ Gives an overview of the JDK supplied classes and a short description of the methods

▮ The JDK classes grouped into packages!

http://download.oracle.com/javase/8/docs/api/


Shows a brief description of all packages in V8

Or click a class in the index on the left

Click the package name to see all classes in the package


Shows a hierarchy for the class

Brief description and examples


A list and brief summary of the methods in the class


Documentation

▮ You can generate the same documentation for your classes

▮ First, you may have to tell RAD where the javadoc command is (in the JDK)

▮ In our case: F:\jdk\bin\javadoc.exe


Right click the class and select Export


Select Javadoc and click Next


Specify where the documentation should go, click Finish

RAD should know that javadoc is in the JDK in RAD



Console shows Javadoc messages


.html file with same name as class is there

Double click to display in browser


The “signature” of each method is shown

Signature = method name + parameters

The signature uniquely defines each method, not the name


Non-graded Assg

▮ Create Cust1

▮ Export Cust1 and Run

▮ Export Cust1 documentation

▮ Send Cust1.java, Cust1.class, and Cust1.html files as email attachments to [email protected]

Documents

Chapter 2© copyright Janson Industries 20141 Java ▮ Java/PC programming environment ▮ Java syntax rules ▮ Java documentation ▮ Java/RAD coding example