Graphical User Interface Programming

Graphical User Interface Programming

Dr. Susan McKeever (not me)Email: [email protected]

www.comp.dit.e/rlawlor

UI Programming

• At the end of the course you will be able to:– Develop GUI applications– Use standard UI components– Develop custom UI components

– And… Program in Java– And.. Be a better programmer

Admin…

• Assessment:– 1 formal exam = 50%

– 1 assignment + in class test = 35%– Lab marks = 15%

Admin

• Contact Hours:– 1 hour lecture – 2 hour lab session – 1 hour tutorial

Admin

• Tutorial/Lecture/Lab– Lecture

• Provide new material• Usually new Lab exercises

– Lab• Work on latest Lab Sheet• Lab content will be a week behind the lecture..

– Tutorial • Discuss issues from last Lab Sheet• Review Broken Code/error messages

Course..

• Topics– Java Language Basics

• Hello World• Operators/Reference

Types• OO Basics• Packages• Abstractions• Exceptions

• Connecting to Databases JDBC

• “Good” programming practices

– GUIs (Java Swing)• Layout Managers• Event Handing• Graphics• Applets• GUI Design• Class structures and Model

View Controller (MVC)

Resources…

• Resources– Web, web, web, web, web, web,………………– JAVA API http://download.oracle.com/javase/6/docs/api/– Textbook:

UI Programming: Paul Fischer, An Intro to GUIs with Java SwingGeneral Reference: Java in a Nutshell, O’Reilly

Java Swing, O’Reilly 2nd Ed.

• Webcourses – www.comp.dit.ie/smckeever– CHECK YOU CAN ACCESS.. IF NOT EMAIL ME– Lecture notes– Lab Assignments & eventually Solutions– Assignments (Details and Submission)– Links to Useful References– Past Exam Papers.. Just 1 set..

Important

• Lecture notes are my guide to structuring lectures

• They do not contain all material covered• Will do plenty of work/examples etc on

the board

Introduction toJava Programming

Java Editions

Java2 Standard Edition

(J2SE™)

Java2 Enterprise Edition

(J2EE™)

Java2 Micro Edition

(J2ME™)

Java 2 Platform

Standard desktop &workstation applications; applets

Heavy duty serverSystems – mediumto large companies

Small & memory constrained devices

Key Benefits of Java

• Java is “write once, run anywhere”– architecture neutral– portable across different platforms– Due to Java Virtual Machine (JVM)

• Security features– highly configurable security levels prevent

any piece of Java code doing harm to the host system

Key Benefits of Java

• Network-centric platform– easy to work with resources across a

network and to create network based applications

• Object Oriented– an interacting collection of independent

software components– dynamic extensible programs

Key Benefits of Java• Internationalisation

– uses 16 bit Unicode characters that represents the phonetic and ideographic character sets of the entire world

• Performance– although an interpreted language Java

programs run almost as fast as native C, C++ programs

• Simple and easy to develop– powerful & well designed set of APIs– http://download.oracle.com/javase/6/docs/

api/

JVM

class myCode {…………

}

myCode.java

Compiled by Java compiler

Application runs

Interpreted by JVM

Source Code

1001100101001……

myCode.class

Bytecode

JVM

• JVM provides the run time environment for the bytecode (Java Runtime Environment JRE)– executes the bytecode and causes native

machine code instructions to execute on the CPU that the JVM is on

each target platform needs an implementation of the JVM

The Simplest Java Program

public class HelloWorld{

// no fields

// main methodpublic static void main (String []

args){

System.out.println("Hello World..");

}}

Basic Program structure• Basic class definition - remember from OO

programming last year?

class className {

// field declarations…// method declarations…

}

Class versus Object?

The Simplest Java Program


// no fields


args){


}}To run a java program, you need a special methods called the main method to tell the program where to start executing

Simple Java Program


// no fields


args){


}}

command line args

accessible to all classes(info hiding)

indicates class method

invoking a member

returns nothing

Not much point in creating an object out of this class.. It doesn’t describe anything.. It just “runs”

Objects

• An object includes state (fields) and behaviour (methods)

• A class object is the blueprint for the instance objects

• All code must be included in a class– no inline functions like C++

An Example Class

• Want to create a class that represents a student.

• Want to store a “name” for the student. • How?

• Want to the class to have a way to print out the student name• How?

An Example Class

public class Student {// member fieldsprivate String name;

// constructorpublic Student(String name) {

this.name=name;}// methodspublic void printDetails(){

System.out.println("\nName: “ + name);}

}

An Example Class

public class Student {// member fieldsprivate String name;// constructorpublic Student(String name) {


System.out.println("\nName: “ + name);}

}

a business

class

String concatenati

on

predefined Java class

no return type reference to

the object itself

accessibility

Instantiation (i.e. creating objects out of a class)

• Class definition used to create a “class object” at runtime

• E.g. created a Student class.. Now want to create a “real” student object

• To instantiate “instance objects” use new operatorClassName myInstance = new ClassName();

where ClassName() is a constructor Note: no need to allocate the memory for

the object like in C++

Using a Class in a Program

public class myProg {public static void main(String args []){ // instantiate a Student object Student student1= new Student("Joe Bloggs"); Student student2= new Student(“Liz mckeever"); // invoke printDetails method student1.printDetails(); student2.printDetails();}

}

the program control class:

Contains “main”

source file called

myProg.java

Using the JDK

• Each class is stored in a source file “xxx.java”

• The name of source file should be the same as the name of class

public class myCode {…………

}

myCode.java

Source File

Compiling your source code

• Compile each class source file into bytecode (class files)

• In DOS To compile a java source file javac myCode.java

• This creates a classfile called myCode.class

BUT.. This year we’re going to use Eclipse

1001101001110101011…………

myCode.class

Class File

Eclipse

An Integrated Development Environment (IDE)

Originally created by IBM (2001)

Open source community, free

Widely widely used in industry

Increases coding efficiency Spots compile errors as you type Allows quick fixes Helps file organisations/packages Imports are easy Demo..

Eclipse

• Free to download• Worth doing..• http://www.eclipse.org/

To run your program

• All so easy in Eclipse..

–Click the “RUN” command in Eclipse – full instructions at the lab

Using a Control Class// This is in a file call myControlClass.javapublic class myControlClass {

public static void main(String args []){

// instantiate a Student object

new StudentPrinter();

}}

Using a Control Class// This is in a file call StudentPrinter.javapublic class StudentPrinter {

// Constructor - instantiate a Student object public StudentPrinter() { Student student1= new Student("Joe Bloggs"); Student student2= new Student(“Liz mckeeve"); // invoke printDetails method student1.printDetails(); student2.printDetails();

}}

Using a Control Class// This is in a file call Student.javapublic class Student {

// member fieldsprivate String name;// constructorpublic Student(String name){


System.out.println("\nName: " + name);}

}

General points to note..

• 80% of the cost of software is on maintaining code– Typically not the original developer

• “You cannot be good at s/w development if you don’t make it as easy as possible for someone else to maintain your code”

• Dr. Susan McKeever Sept 2012

• ??

How?

Common sense

• Comment your code– Header at the top of your code– Every method explained

• Use meaningful names for variables, classes, objects...

• Use java conventions (see overleaf)• Many more.. To be covered.

Use Conventions.. • Java is Case sensitive• Use the conventions

– Classes should be nouns, capitalised first letter e.g.

Student, ImagePixel– Variables mixed case starting with lower.

E.g. acctBalance, line– Constant are all upper case e.g.

COLOR_RED– Methods are verbs, mixed case starting

with lower e.g. getBalance()

Java Syntax

Primitive data typesOperatorsControl statements

Java Syntax part 1

Primitive data types

• Using a variable in java.. You must declare what type of data can contain..– int, char etc..

• A primitive type is predefined by the language and is named by a reserved keyword.... 8 of them in java


• char (16 bits) a Unicode character• byte (8 bits)• int (32 bits) a signed integer• short (16 bits) a short integer • long (64 bits) a long integer


• float (32 bits) a real number• double (64 bits) a large real number• boolean (8 bits)

– values are true or false (keywords)– Used with control statements e.g. while, do

, if – e.g. while (fileEmpty)

Operators

• Additive+ -

• Multiplicative* / %

• Equality (tests)== !=

• Assignment operators= += -= *= /= %=

Operators

• Relational operators< <= > >=

• Increment operators (postfix and prefix)++ --

• Conditional operator (short cut for if/else

?: e.g. max = (a > b) ? a : b;• String concatenation

+

Logical Operators

• Not !

• Logical AND &&• Logical OR ||

Control Statements

• Similar to C/C++ syntax:– if statement

if (x != n){ …}else if {

… }else {

… }

– for statement for (int i=0; i<max; i++){

… };

Control Statements

–while statement while (x==n ){

…};

–do statement do {…} while( x<=y && x!=0);

Control Statements

– switch statement switch (n){ case 1:

… break;case 2: case 3:

… break;default: break;

};

Java Reference Types

ClassesArrays

Java Syntax Part 2

Reference Types

• Classes and arrays are composite types – no standard size– contain other elements

• Manipulated “by reference’’ to the object or array

• Primitive data types manipulated “by value”

Reference vs Primitive Types

• A reference is a value that refers to the object or array

• A primitive datatype holds the value directly• Difference to primitive types effects the way

values are copied and comparedSetting Object A = Object B only sets the

reference and does not set the contentsComparing Object A and Object B, A will not be

equal to B even if they have the same contents

References in Java

• Note: – Java does not support the & address-of or

-> and * de-reference operators of C and C++

– the . operator in Java is more like the -> operator of C++

– references in Java cannot be manipulated (e.g. incremented or decremented)

null

• null – is a special value indicating a reference to

nothing– can be assigned to a variable of any

reference type

Arrays in Java

• Array declaration – set the (1) size or (2) the values:(1)type arrayId[] = new type[limit]; (2)type arrayId[] = new type[] {values};

• Multi dimensional array:type arrayId[][] =new type[rowlimit][colLimit]

• Examples:int frequencies[]= new int[]{20,40,60}; String countryCode[]= new String[176]; double table[]=new double[4][5];

Arrays in Java

• Arrays can be formed from any data type or class

• Arrays are indexed from 0.• Arrays are fixed size but the size can be

allocated at run time:e.g. int array1[]; // declare array… …int size=n; // get array size,

array1 = new int [size]; // allocate array

• Assigning one array to another array copies the reference and does not copy full array.

Arrays in Java

• Accessing an array element that does not exist will result in an error

• The length of an array can be accessed using a read-only property called length that is associated with every array.e.g. for (i=0; i<frequencies.length; i++)…

• Arrays can be passed as parameters to methodse.g. main (String [] args)

Class & Array Interaction

• There are 3 ways that classes and arrays are used together(1) An array of a class of objects:Student students[] =new Student[8];

(2) A class containing an array and methods that act on it

(3) A class containing methods that operate on array parameters

Class & Array Interaction (2) A class containing an array and methods that act on it

class IntArray {private int arrayOfInt[];IntArray(int size){ //constructor arrayOfInt=new int [size];}int get(int index){ // get value at index return arrayOfInt[index];}void set (int index, int value){ //set value arrayOfInt[index]=value;}public String toString(){ // print out array String s =””; for (int i=0; i<arrayOfInt.length;i++) s += “ “+arrayOfInt[i]; return s;}

}

Class & Array Interaction (3) A class containing methods that operate on array parameters

class ArrayUtilities {

static int max( int arrayA [] ) { // finds the max element of

arrayA // and returns it ...

return arrayA[i];}

static void sort (int [] arrayA) { //sorts the elements of arrayA

... } }

Array passed into to the

“sort” method as a parameter

Documents

Graphical User Interface Programming