Advanced java programming - awt packages

UNIT - II GUI and I/O PROGRAMMING AWT package – Layouts – Event Package – Event Model – Painting- Swing Fundamentals- Swing Classes-Working with Text Fields, Buttons, List and Scroll panes - Input Output Package

AWT Packages ■ AWT is an API that is responsible for building the Graphical User Interface. It is part of the java foundation classes(JFC) ■ AWT includes a rich set of user interface component , a powerful event handling model ,graphics and image tools, layout manager etc., ■ AWT supports java bean Architecture. Every AWT component is a simple java bean. ■ The java awt package contains all classes for creating user interfaces and for painting graphics and images Graphics primitives that allow the drawing and rendering of lines and images Components such as labels, buttons and text fields Containers that include frames ,panels and dialogs Layout managers that control the display in a portable

APPLET Java Programs Application Applets Application Simple stand alone program that can run using Java interpreter from the command line. Applets Run from inside a world wide web browser that supports java applets 3

4 Example: A "Life" applet Container (Applet) Containers (Panels) Component (Canvas) Components (Buttons) Components (Labels) Components (TextFields)

APPLET ■ Applet have restrictions to ensure security and to prevent them from being affected by viruses. These are Applets cannot read or write to the file system Applets cannot communicate with any other server than the one in which they were stored originally. Applets cannot run any program on the system 5

6 Applets ■ An application has a public static void main(String args[ ]) method, but an Applet usually does not ■ An Applet's main method is in the Browser ■ To write an Applet, you extend Applet and override some of its methods ■ The most important methods are init( ), start( ), and paint(Graphics g)

7 To create an applet ■ public class MyApplet extends Applet { … } ■ this is the only way to make an Applet ■ You can add components to the applet ■ The best place to add components is in init( ) ■ You can paint directly on the applet, but… ■ …it’s better to paint on a contained component ■ Do all painting from paint(Graphics g)

Steps to create Applet //myapplet.java import java.awt.*; import java.applet.*; public class myapplet extends java.applet.Applet { public void paint(Graphics g) { g.drawstring(“J.Vanitha”,70,300); }} 8

Drawing Lines,Rectangles,Ovals Methods ❖drawLine(int x1,int y1,int x2,int y2) ❖drawRect(int x1,int y1,int width, int height) ❖fillRect(int x1,int y1,int width, int height) ❖drawOval(int x1,int y1,int width, int height) ❖fillOval(int x1,int y1,int width, int height) 10

import java.applet.Applet; import java.awt.*; public class NewApplet extends Applet {public void paint(Graphics g) { g.drawLine(40,30,200,30); g.drawRect(40,60,70,40); g.fillRect(140,60,70,40); g.drawOval(240,120,70,40); g.fillOval(40,180,70,140); }} 11

Paint Major Operations Drawing and Filling Color Write Text Set Font Clip 1.Set the color g.setColor(Color.RED); 2.Set the Font Font f=new Font(“TimesNewRoman”,Font.BOLD,<fontsize>); g.setFont(f); 13

Paint 3.Draw a Text g.drawString(“text”,xpos,ypos); 4.Drawing and Filling g.drawRect(x1,y1,x2,y2); g.fillOval(x1,y1,x2,y2); 5.Clip g.setClip(x,y,width,height); 14

Human Face import java.awt.*; import java.applet.*; public class drawface extends Applet{ Public void paint(Graphics g){ g.drawOval(40,40,120,150); g.drawOval(57,75,30,20); g.drawOval(110,75,30,20); g.fillOval(68,81,10,10); g.fillOval(121,81,10,10); g.drawOval(85,100,30,30); g.fillArc(60,125,80,40,180,180); g.drawOval(25,92,15,30); g.drawOval(160,92,15,30); }} 15

16 Containers and Components ■ The job of a Container is to hold and display Components ■ Some common subclasses of Component are Button, Checkbox, Label, Scrollbar, TextField, and TextArea ■ Some Container subclasses are Panel (and Applet), Window, and Frame

17 Some types of components Label Button Button Checkbox Choice List Scrollbar TextField TextArea CheckboxGroup Checkbox

18 Creating components Label lab = new Label ("Hi, Dave!"); Button but = new Button ("Click me!"); Checkbox toggle = new Checkbox ("toggle"); TextField txt = new TextField ("Initial text.", 20); Scrollbar scrolly = new Scrollbar (Scrollbar.HORIZONTAL, initialValue, bubbleSize, minValue, maxValue);

19 Adding components to the Applet class MyApplet extends Applet { public void init () { add (lab); // same as this.add(lab) add (but); add (toggle); add (txt); add (scrolly); ...

Layout Manager ■ Layout manager is an instance of any class that implements the layout manager interface ■ The layout manager is set by the setLayout() method ■ General form is void setLayout(layoutManager obj) ■ Layout Manager classes i) FlowLayout ii) BorderLayout iii) GridLayout iv) CardLayout 20

21 FlowLayout Constructor Description FlowLayout() Constructs a new flow layout with center alignment, leaving a vertical and horizontal gap 5 pixels FlowLayout (int align) Constructs a new flow layout with the alignment specified leaving a vertical and horizontal gap of 5 pixels FlowLayout (int align, int vgap, int hgap) Constructs a new flow layout with the alignment specified, leaving a vertical and horizontal gap as specified

22 Complete example: FlowLayout import java.awt.*; import java.applet.*; public class FlowLayoutExample extends Applet { public void init () { setLayout (new FlowLayout ()); // default add (new Button ("One")); add (new Button ("Two")); add (new Button ("Three")); add (new Button ("Four")); add (new Button ("Five")); add (new Button ("Six")); } }

23 BorderLayout ■ At most five components can be added ■ If you want more components, add a Panel, then add components to it. ■ setLayout (new BorderLayout());

24 BorderLayout Constructor Description BorderLayout() Creates a new border layout with no gap between the components Border Layout(int hgap,int vgap) Creates a border layout with the specified horizontal and vertical gap between components

25 BorderLayout with five Buttons public void init() { setLayout (new BorderLayout ()); add (new Button ("NORTH"), BorderLayout.NORTH); add (new Button ("SOUTH"), BorderLayout.SOUTH); add (new Button ("EAST"), BorderLayout.EAST); add (new Button ("WEST"), BorderLayout.WEST); add (new Button ("CENTER"), BorderLayout.CENTER); }

26 Complete example: BorderLayout import java.awt.*; import java.applet.*; public class BorderLayoutExample extends Applet { public void init () { setLayout (new BorderLayout()); add(new Button("One"), BorderLayout.NORTH); add(new Button("Two"), BorderLayout.WEST); add(new Button("Three"), BorderLayout.CENTER); add(new Button("Four"), BorderLayout.EAST); add(new Button("Six"), BorderLayout.SOUTH); } }

27 Using a Panel Panel p = new Panel(); add (p, BorderLayout.SOUTH); p.add (new Button ("Button 1")); p.add (new Button ("Button 2"));

28 Grid Layout Constructor Description GridLayout() Creates a grid layout with a default of one column per components in a single row GridLayout(int rows, int columns) Creates a grid layout with the specified rows and columns GridLayout(int rows,int columns,int hgap,int vgap) Creates a grid layout with the specified rows and columns and specified horizontal and vertical gaps.

29 GridLayout ■ The GridLayout manager divides the container up into a given number of rows and columns: new GridLayout(rows, columns) ■ All sections of the grid are equally sized and as large as possible

30 Complete example: GridLayout import java.awt.*; import java.applet.*; public class GridLayoutExample extends Applet { public void init () { setLayout(new GridLayout(2, 3)); add(new Button("One")); add(new Button("Two")); add(new Button("Three")); add(new Button("Four")); add(new Button("Five")); } }

31 CardLayout Constructor Description CardLayout() Creates a new card layout with no gap between the components CardLayout(int hgap,int vgap) Creates a card layout with the specified horizontal and vertical gap between components

32 CONTAINERS Object Component Container Panel Applet Window Frame Dialog A AWT container object is component that can contain other AWT components. Frame f=new Frame(); f.add(new Button(“OK”)); f.setSize(1000,1000); f.setVisible(true); Panel p=new Panel(); p.add(new Button(“OK”));

Events ■ Java uses an Event Delegation Model. ■ Every time a user interacts with a component on the GUI, events are generated. ■ Events are component-specific. ■ Events are objects that store information like ■ the type of event that occurred, ■ the source of the event, ■ the time of an event to name a few.

Event Delegation Model ■ Once the event is generated, then the event is passed to other objects which handle or react to the event, thus the term event delegation. ■ The objects which react to or handle the events are called event listeners.

Three Players ■ Event source which generates the event object. Eg. button ■ Event listener which receives the event object and handles it Eg. ActionListener ■ Event object that describes the event Eg. ActionEvent e

AWT Events •The following is a list of events in the java.awt.event package: • ActionEvent - Action has occurred (eg. button pressed) • AdjustmentEvent - "Adjustable" Component changed • ComponentEvent - Component Changed • ContainerEvent - Container changed (add or remove) • FocusEvent - Focus Changed • HierarchyEvent - Change in Component Hierarchy • InputEvent - Superclass of KeyEvent and MouseEvent • InputMethodEvent - Text Input Events • ItemEvent - Item Selected or Deselected • KeyEvent - Keyboard event • MouseEvent - Mouse event • PaintEvent - Low level; do not use. • TextEvent - Text Changed events • WindowEvent - Window related Events

•The Following events have Listeners associated with them: • ActionEvent - ActionListener • AdjustmentEvent - AdjustmentListener • ComponentEvent - ComponentListener • ContainerEvent - ContainerListener • FocusEvent - FocusListener • HierarchyEvent - HierarchyListener • InputMethodEvent - InputMethodListener • ItemEvent - ItemListener • KeyEvent - KeyListener • MouseEvent - MouseListener - MouseMotionListener • TextEvent - TextListener • WindowEvent - WindowListener Listener Interfaces

A Few More Java Events ■ FocusEvent – component gains or loses focus ■ MouseEvent – mouse is moved, dragged, pressed, released or clicked ■ WindowEvent – window is iconified, deiconified, opened or closed ■ TextEvent – text is modified ■ KeyEvent – key is pressed, depressed or both ■ ContainerEvent – components are added or removed from Container

Corresponding Listeners ■ FocusEvent – FocusListener ■ MouseEvent – MouseListenerMouseListener, MouseMotionListener ■ WindowEvent – WindowStateListenerWindowStateListener, WindowListenerWindowStateListener, WindowListener, WindowFocusListener ■ TextEvent – TextListener ■ KeyEvent – KeyListener ■ ItemEvent- ItemListener ■ ContainerEvent – ContainerListener

40 Step 1:import java.awt.*; import java.awt.event.*; Step 2: Inherit interface ActionListener class <sample1> implements ActionListener { } Step 3:Declare variable Frame f; Button b; TextField tf1;

41 Step 4:constructor definion Sample1() Step 5:Within constructor declare variable f=new Frame("My Frame"); f.setLayout(new FlowLayout()); b = new Button("ok"); l=new TextField("",20); Step 6:Add listener to the components and add in the frame b.addActionListener(this); f.add(b); f.add(l); f.setSize(1000,1000); f.setVisible(true); EVENT SOURCE

Step 7:Add method for ActionListener public void actionPerformed(ActionEvent e) { if(e.getSource()==b) { l.setText("Ouch!"); } } 42 Event Object EVENT LISTENE R

Step 8:Add main method and create object for the class public static void main(String arg[]) { sample1 m=new sample1(); } 43

44 MyButtonListener import java.awt.*; import java.awt.event.*; public class sample1 implements ActionListener { Button b; Frame f; TextField l; sample1() { f=new Frame("My Frame"); f.setLayout(new FlowLayout()); b = new Button("ok"); b.addActionListener(this); f.add(b); l=new TextField("",20); f.add(l); f.setSize(1000,1000); f.setVisible(true); }

45 public void actionPerformed(ActionEvent e) { if(e.getSource()==b) { l.setText("Ouch!"); } } public static void main(String arg[]) { sample1 m=new sample1(); } }

46 import java.awt.*; import java.awt.event.*; public class sample1 implements ActionListener { Button b,b1; Frame f; TextField l; sample1() { f=new Frame("My Frame"); f.setLayout(new FlowLayout()); b = new Button("ON"); b.addActionListener(this);

47 b1 = new Button("OFF"); b1.addActionListener(this); f.add(b); f.add(b1); l=new TextField("",20); f.add(l); f.setSize(1000,1000); f.setVisible(true); }

48 public void actionPerformed(ActionEvent e) { if(e.getSource()==b) { l.setText("ON"); } else if(e.getSource()==b1) { l.setText("OFF"); } } public static void main(String arg[]) { sample1 m=new sample1(); }}

Garbage ■ Garbage collection (GC) - automatic management of dynamically allocated storage ■ It is the process of automatically finding memory blocks that are no longer being used and making them available again ■ When a java object become unreachable to the program it is subjected to garbage collection ■ Objects are dynamically allocated by using the new operator how such objects are destroyed and their memory released for later reallocation

■ Java handle deallocation automatically. This technique is called garbage collection ■ Protected void finalize() { - - } To reclaim the destroy object like recycle bin 51

Multithreading The objectives of this chapter are: • To understand the purpose of multithreading • To describe Java's multithreading mechanism • To explain concurrency issues caused by multithreading •To outline synchronized access to shared resources

•Multithreading is similar to multi-processing. •A multi-processing Operating System can run several processes at the same time • Each process has its own address/memory space • The OS's scheduler decides when each process is executed • Only one process is actually executing at any given time. However, the system appears to be running several programs simultaneously •Separate processes to not have access to each other's memory space • Many OSes have a shared memory system so that processes can share memory space • In a multithreaded application, there are several points of execution within the same memory space. • Each point of execution is called a thread • Threads share access to memory What is Multithreading?

•In a single threaded application, one thread of execution must do everything • If an application has several tasks to perform, those tasks will be performed when the thread can get to them. • A single task which requires a lot of processing can make the entire application appear to be "sluggish" or unresponsive. • In a multithreaded application, each task can be performed by a separate thread • If one thread is executing a long process, it does not make the entire application wait for it to finish. • If a multithreaded application is being executed on a system that has multiple processors, the OS may execute separate threads simultaneously on separate processors. Why use Multithreading?

•Any kind of application which has distinct tasks which can be performed independently • Any application with a GUI. • Threads dedicated to the GUI can delegate the processing of user requests to other threads. • The GUI remains responsive to the user even when the user's requests are being processed • Any application which requires asynchronous response • Network based applications are ideally suited to multithreading. • Data can arrive from the network at any time. • In a single threaded system, data is queued until the thread can read the data • In a multithreaded system, a thread can be dedicated to listening for data on the network port • When data arrives, the thread reads it immediately and processes it or delegates its processing to another thread What Kind of Applications Use Multithreading?

•Each thread is given its own "context" • A thread's context includes virtual registers and its own calling stack • The "scheduler" decides which thread executes at any given time • The VM may use its own scheduler • Since many OSes now directly support multithreading, the VM may use the system's scheduler for scheduling threads • The scheduler maintains a list of ready threads (the run queue) and a list of threads waiting for input (the wait queue) •Each thread has a priority. The scheduler typically schedules between the highest priority threads in the run queue • Note: the programmer cannot make assumptions about how threads are going to be scheduled. Typically, threads will be executed differently on different platforms. How does it all work?

•Few programming languages directly support threading • Although many have add-on thread support • Add on thread support is often quite cumbersome to use •The Java Virtual machine has its own runtime threads • Used for garbage collection •Threads are represented by a Thread class • A thread object maintains the state of the thread • It provides control methods such as interrupt, start, sleep, yield, wait •When an application executes, the main method is executed by a single thread. • If the application requires more threads, the application must create them. Thread Support in Java

• Threads can be in one of four states • Created, Running, Blocked, and Dead • A thread's state changes based on: • Control methods such as start, sleep, yield, wait, notify • Termination of the run method Thread States Created Runnable Blocked Dead start() Thread() run() method terminates sleep() wait() notify()

•The thread class has a run() method • run() is executed when the thread's start() method is invoked •The thread terminates if the run method terminates • To prevent a thread from terminating, the run method must not end • run methods often have an endless loop to prevent thread termination •One thread starts another by calling its start method • The sequence of events can be confusing to those more familiar with a single threaded model. How does a Thread run? Thread1 Thread Object start() Thread2 run()

•The obvious way to create your own threads is to subclass the Thread class and then override the run() method • This is the easiest way to do it • It is not the recommended way to do it. • Because threads are usually associated with a task, the object which provides the run method is usually a subclass of some other class • If it inherits from another class, it cannot inherit from Thread. •The solution is provided by an interface called Runnable. • Runnable defines one method - public void run() •One of the Thread classes constructor takes a reference to a Runnable object • When the thread is started, it invokes the run method in the runnable object instead of its own run method. Creating your own Threads

•In the example below, when the Thread object is instantiated, it is passed a reference to a "Runnable" object • The Runnable object must implement a method called "run" • When the thread object receives a start message, it checks to see if it has a reference to a Runnable object: • If it does, it runs the "run" method of that object • If not, it runs its own "run" method Using Runnable Thread1 Thread Object start() Thread2 run() Runnable Object run()

Runnable Object Example Code public class Test implements Runnable { private Thread theThread; public void start() { if (theThread == null) { theThread = new Thread(this); theThread.start(); } } public void run() { // This method runs in its // own thread } Thread1 Thread Object start() Thread2 run() run() start() Thread(Runnable)

•In Java 1.1, the Thread class had a stop() method • One thread could terminate another by invoking its stop() method. • However, using stop() could lead to deadlocks • The stop() method is now deprecated. DO NOT use the stop method to terminate a thread • The correct way to stop a thread is to have the run method terminate • Add a boolean variable which indicates whether the thread should continue or not • Provide a set method for that variable which can be invoked by another thread Properly Terminating Threads

public class Test implements Runnable { private Thread theThread; private boolean stopThread = false; public void start() { if (theThread == null) { theThread = new Thread(this); theThread.start(); } } public void setStopThread(boolean aValue) { stopThread = aValue; } public void run() { while(true) { if (stopThread) break; // .... Terminating Thread Example

•The previous example illustrates a Runnable class which creates its own thread when the start method is invoked. •If one wished to create multiple threads, one could simple create multiple instances of the Runnable class and send each object a start message • Each instance would create its own thread object •Is the a maximum number of threads which can be created? • There is no defined maximum in Java. • If the VM is delegating threads to the OS, then this is platform dependent. • A good rule of thumb for maximum thread count is to allow 2Mb of ram for each thread • Although threads share the same memory space, this can be a reasonable estimate of how many threads your machine can handle. Creating Multiple Threads

•Every thread is assigned a priority (between 1 and 10) • The default is 5 • The higher the number, the higher the priority • Can be set with setPriority(int aPriority) • The standard mode of operation is that the scheduler executes threads with higher priorities first. • This simple scheduling algorithm can cause problems. Specifically, one high priority thread can become a "CPU hog". • A thread using vast amounts of CPU can share CPU time with other threads by invoking the yield() method on itself. •Most OSes do not employ a scheduling algorithm as simple as this one • Most modern OSes have thread aging • The more CPU a thread receives, the lower its priority becomes • The more a thread waits for the CPU, the higher its priority becomes • Because of thread aging, the effect of setting a thread's priority is dependent on the platform Thread Priorities

•Sometimes a thread can determine that it has nothing to do • Sometimes the system can determine this. ie. waiting for I/O • When a thread has nothing to do, it should not use CPU • This is called a busy-wait. • Threads in busy-wait are busy using up the CPU doing nothing. • Often, threads in busy-wait are continually checking a flag to see if there is anything to do. •It is worthwhile to run a CPU monitor program on your desktop • You can see that a thread is in busy-wait when the CPU monitor goes up (usually to 100%), but the application doesn't seem to be doing anything. • Threads in busy-wait should be moved from the Run queue to the Wait queue so that they do not hog the CPU • Use yield() or sleep(time) • Yield simply tells the scheduler to schedule another thread • Sleep guarantees that this thread will remain in the wait queue for the specified number of milliseconds. Yield() and Sleep()

•Those familiar with databases will understand that concurrent access to data can lead to data integrity problems •Specifically, if two sources attempt to update the same data at the same time, the result of the data can be undefined. •The outcome is determined by how the scheduler schedules the two sources. • Since the schedulers activities cannot be predicted, the outcome cannot be predicted •Databases deal with this mechanism through "locking" • If a source is going to update a table or record, it can lock the table or record until such time that the data has been successfully updated. • While locked, all access is blocked except to the source which holds the lock. •Java has the equivalent mechanism. It is called synchronization • Java has a keyword called synchronized Concurrent Access to Data

•In Java, every object has a lock • To obtain the lock, you must synchronize with the object •The simplest way to use synchronization is by declaring one or more methods to be synchronized • When a synchronized method is invoked, the calling thread attempts to obtain the lock on the object. • if it cannot obtain the lock, the thread goes to sleep until the lock becomes available • Once the lock is obtained, no other thread can obtain the lock until it is released. ie, the synchronized method terminates • When a thread is within a synchronized method, it knows that no other synchronized method can be invoked by any other thread • Therefore, it is within synchronized methods that critical data is updated Synchronization

•If an object contains data which may be updated from multiple thread sources, the object should be implemented in a thread-safe manner • All access to critical data should only be provided through synchronized methods (or synchronized blocks). • In this way, we are guaranteed that the data will be updated by only one thread at a time. Providing Thread Safe Access to Data public class SavingsAccount { private float balance; public synchronized void withdraw(float anAmount) { if ((anAmount>0.0) && (anAmount<=balance)) balance = balance - anAmount; } public synchronized void deposit(float anAmount) { if (anAmount>0.0) balance = balance + anAmount; }

•However, there is an overhead associated with synchronization • Many threads may be waiting to gain access to one of the object's synchronized methods • The object remains locked as long as a thread is within a synchronized method. • Ideally, the method should be kept as short as possible. •Another solution is to provide synchronization on a block of code instead of the entire method • In this case, the object's lock is only held for the time that the thread is within the block. • The intent is that we only lock the region of code which requires access to the critical data. Any other code within the method can occur without the lock. • In high load situations where multiple threads are attempting to access critical data, this is by far a much better implementation. Thread Safety Performance Issues

public class SavingsAccount { private float balance; public void withdraw(float anAmount) { if (anAmount<0.0) throw new IllegalArgumentException("Withdraw amount negative"); synchronized(this) { if (anAmount<=balance) balance = balance - anAmount; } } public void deposit(float anAmount) { if (anAmount<0.0) throw new IllegalArgumentException("Deposit amount negative"); synchronized(this) { balance = balance + anAmount; } } Block Synchronization

■ The basic language functions are stored in a package inside of the java package called java.lang. ■ Normally, you have to import every package or class that you want to use, but since Java is useless without much of the functionality in java.lang, it is implicitly imported by the compiler for all programs. ■ import java.lang.*; 74

■ Inside the standard package java.lang, Java defines several exception classes. ■ java.lang includes the following classes: ■ Boolean Long StackTraceElement ■ Byte Math StrictMath (Java 2,1.3) ■ Character Number String ■ Class Object StringBuffer ■ Loader Package (Java 2) System ■ Compiler Process Thread 75

Input Output Packages ■ The java.io package contains nearly every class you might ever need to perform input and output (I/O) in Java. ■ All these streams represent an input source and an output destination. The stream in the java.io package supports many data such as primitives, Object, localized characters, etc. ■ A stream can be defined as a sequence of data. The InputStream is used to read data from a source and the OutputStream is used for writing data to a destination. ■ Java provides strong but flexible support for I/O related to Files and networks but this tutorial covers very basic functionality related to streams and I/O. 77

Assignment Check the number odd or even. Insert into separate file. 81

A first Swing application import javax.swing.*; public class FirstGUI { public static void main(String[] args) { JFrame f = new JFrame(); f.setVisible(true); } } When you run this program, a tiny window appears: The close button does not work (have to press “Stop” in Ready) Class for drawing a window on the screen Displays the window and enters the event loop.

Shutting down the application properly import javax.swing.*; public class FirstGUI { public static void main(String[] args) { JFrame f = new JFrame( ); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.setVisible(true); } } • To give the application a title, give the constructor a string: JFrame f = new JFrame( “My first GUI”); Need to add a single statement to program the close button

Components and containers ■ A component is any GUI element, such as a window, button or label. ■ A container is a type of component that has the purpose of containing other components. ■ Types of containers: ■ Top-level containers: Every Swing program contains at least one top-level container (e.g. JFrame, JDialog or JApplet). Top-level containers cannot be added to other containers. ■ Intermediate containers: used to group components so that they can be handled as a single component (e.g JPanel, JTabbedPane). ■ Atomic components (basic controls): cannot contain other components (e.g JButton, JTextField).

Examples of Atomic Components Often called widgets: ■ Label – used to put a label next to another component ■ Button – used to make the program “do something” ■ Checkbox component – used for yes/no, true/false response from user ■ Choice component – drop-down list ■ TextField – used to type single line of text ■ … etc

Adding a button to the application import javax.swing.*; public class FirstGUI { public static void main(String[] args) { JFrame f = new JFrame( ); JButton button = new JButton("Press me!"); // create a button f.getContentPane().add(button); // add the button to the frame f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.pack( ); f.setVisible(true); } }

Organising the code in a better way ■ As we start adding more components, the main method will become too large and messy. ■ A better way: ■ Create a class that extends JFrame ■ Put all components into the class (as data members) ■ Do the rest in the constructor import javax.swing.*; public class SimpleFrame extends JFrame { private JButton button = new JButton("Press me!"); public SimpleFrame( ) { getContentPane( ).add(button); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); pack(); } }

Creating a SimpleFrame object ■ SimpleFrame extends JFrame, therefore s is also a JFrame object (and so we can call the setVisible method). ■ In the SimpleFrame class: ■ SimpleFrame defines a specialisation of JFrame by adding an additional component. ■ To call methods of JFrame (such as getContentPane or pack), we no longer need an object handle, since these methods are now inherited from JFrame). public class FirstGUI { public static void main(String[] args) { SimpleFrame s = new SimpleFrame( ); s.setVisible(true); } }

Adding a label ■ To add a label to our application: ■ Create a background, which has both components on it ■ Add this background to our frame ■ In Swing, such a “background” is a component called a panel (JPanel). ■ The diagram on the right is called a component hierarchy (shows how the components fit together) SimpleFrame : (contentPane) JLabel (label) JPanel (background) JButton (exit)

Modified code import javax.swing.*; public class SimpleFrame extends JFrame { private JButton button = new JButton("Press me!"); private JLabel label = new JLabel("Go on, press the button"); private JPanel background = new JPanel(); public SimpleFrame() { background.add(button); // add button to background background.add(label); // add label to background getContentPane().add(background); // add background to frame setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); pack(); } } JLabel used for placing plain text on a GUI JPanel is an intermediate container

Getting the button to do something ■ Currently, if the user clicks on our button, nothing happens. ■ We would like to change the program, so that the label changes when the button is clicked: ■ The code that responds to that event of the user clicking the mouse on our button is called the listener for that button. ■ We would therefore like to program the listener of the button to have the code: label.setText(" Ouch ... that hurt! ");

import javax.swing.*; import java.awt.event.*; public class SimpleFrame extends JFrame { private JButton button = new JButton("Press me!"); private JLabel label = new JLabel("Go on, press the button"); private JPanel background = new JPanel(); public SimpleFrame() { button.addActionListener( new ActionListener() { public void actionPerformed(ActionEvent e) { // code to be executed when button is pushed label.setText("Ouch ... that hurt! "); } }); background.add(button); background.add(label); getContentPane().add(background); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); pack(); } } Code related to event handling

public interface ActionListener extends EventListener { public void actionPerformed(ActionEvent e); }

Review ■ Java provides two sets of facilities for developing GUIs: ■ The Abstract Window Toolkit (AWT): package java.awt ■ Swing: package javax.swing ■ Event-driven ■ mkuttel@cs.uct.ac.za

Event Handling ■ Every time the user types a character or pushes a mouse button, an event occurs. Any object can be notified of the event. All it has to do is implement the appropriate interface and be registered as an event listener on the appropriate event source. : ■ Act that results in the event Listener type: ■ User clicks a button, presses Return while typing in a text field, or chooses a menu item ActionListener ■ User closes a frame (main window) WindowListener ■ User presses a mouse button while the cursor is over a component MouseListener ■ User moves the mouse over a component MouseMotionListener ■ Component becomes visible ComponentListener ■ Component gets the keyboard focus FocusListener ■ Table or list selection changes ListSelectionListener

Button Event javax.swing.AbstractButton javax.swing.JButton addActionListener(ActionListener a) SWING ActionListener AW T actionPerformed(ActionEvent e) (When an ActionEvent occurs, a component notifies its registered ActionListener objects by invoking their actionPerformed methods) (All abstract methods and classes need to be defined)

New Button Event examples ■ First example ■ Improved example

Panels ■ Container that can hold other components ■ “miniature frame” – no title bar or border ■ Panels can contain other panels ■ Each panel can have its own layout JFrame Top Level Component getContentPane() JFrame

Panels ■ Container that can hold other components ■ “miniature frame” – no title bar or border ■ Panels can contain other panels ■ Each panel can have its own layout JPanel (background) One main panel getContentPane.add()

Panels ■ Container that can hold other components ■ “miniature frame” – no title bar or border ■ Panels can contain other panels ■ Each panel can have its own layout JPanel JPanel More panels for organisation background.add()

Panels ■ Container that can hold other components ■ “miniature frame” – no title bar or border ■ Panels can contain other panels ■ Each panel can have its own layout B B B B JTextArea JTextArea Atomic components

Arranging components ■ Layout managers are used to control the size and position of components in containers. ■ The Java platform provides a number of layout managers, including BorderLayout, FlowLayout and GridLayout. ■ To use layout mangers, you have to import java.awt.*. ■ To use a particular layout manager, you use the setLayout method.

import javax.swing.*; import java.awt.*; public class TestFlowLayout extends JFrame { private JButton button1 = new JButton("One"); private JButton button2 = new JButton("Two"); private JButton button3 = new JButton("Three"); private JButton button4 = new JButton("Four"); private JPanel background = new JPanel(); public TestFlowLayout() { background.setLayout(new FlowLayout()); background.add(button1); background.add(button2); background.add(button3); background.add(button4); getContentPane().add(background); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); pack(); } } FlowLayout manager: Buttons are positioned from left to right as they are added. If you resize the window, the buttons are not resized.

import javax.swing.*; import java.awt.*; public class TestBorderLayout extends JFrame { private JButton buttonN = new JButton("North"); private JButton buttonS = new JButton("South"); private JButton buttonE = new JButton("East"); private JButton buttonW = new JButton("West"); private JButton buttonC = new JButton("Center"); private JPanel background = new JPanel(); public TestBorderLayout() { background.setLayout(new BorderLayout()); background.add(buttonN, BorderLayout.NORTH); background.add(buttonS, BorderLayout.SOUTH); background.add(buttonE, BorderLayout.EAST); background.add(buttonW, BorderLayout.WEST); background.add(buttonC, BorderLayout.CENTER); getContentPane().add(background); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); pack(); } } BorderLayout manager: When we add components, we specify a particular position. Not suitable for buttons, but is useful for positioning panels of components.

How BorderLayout resizes The size of the buttons change to fill up the entire area of the window. Note: you do not have to fill all areas in a BorderLayout

Component Hierarchy JButton button1 PackedFrame : (contentPane) JPanel (panelTwo) JPanel (background) JPanel (panelOne) JButton button2 JButton button6 JButton button5 JButton button4 JButton button7 JButton button8 JButton button3 FlowLayout BorderLayout

Understanding what Swing Is ■ Swing is a package that lets you create applications that use a flashy Graphical User Interface (or GUI) instead of a dull console interface. ■ The Swing API provides many different classes for creating various types of user interface elements.

Understanding what Swing Is (Cont’d) ■ Three classes: JFrame, JPanel, and JLabel. These classes are part of a larger collection of classes that are all related through inheritance. ■ The Swing family tree splits at the Component class into one group of classes that are derived from the JComponent class, and another branch that descends from the Window class.

Description of Classes ■ Object: All classes ultimately derive from Object, thus this class is at the top of the tree. ■ Component: represents an object that has a visual representation that can be shown on-screen and that can interact with users. This class defines some basic methods that are available to all Swing classes.

Description of Classes (Cont’d) ■ Container: builds on the basic visual capabilities of the Component class by adding the ability to hold other containers. ■ Window: a specialized type of container object that has a border, a title bar, buttons that minimize, maximize, and close the window, and that can be repositioned and possibly even resized by the user.

Description of Classes (Cont’d) ■ Frame: a type of Window that serves as the basis for Java GUI applications. Frame is an AWT class that has been improved upon by the JFrame class. ■ JFrame: the Swing version of the older Frame class. Most of the Swing applications include at least one JFrame object. ■ JComponent: is the basis for all other Swing components except for frames.

Description of Classes (Cont’d) ■ JPanel: used to organize and control the layout of other components such as labels, buttons, text fields, etc. In most Swing applications, one or more panels are added to a frame. Then, when the frame is displayed, the components that were added to its panels are made visible. ■ JLabel: creates a label that displays a simple text value.

Useful JFrame Constructors and Methods Constructor Description JFrame ( ) Creates a new frame with no title. JFrame (String title) Creates a new frame with the specified title. Method Description void add (Component c) Adds the specified component to the frame.

Useful JFrame Constructors and Methods (Cont’d) Method Description JMenuBar getJMenuBar ( ) Gets the menu for this frame. void pack ( ) Adjusts the size of the frame to fit the components added to it. void remove (Component c) Removes the specified component from the frame.

Useful JFrame Constructors and Methods (Cont’d) Method Description void remove (Component c) Removes the specified component from the frame. void setDefaultCloseOperation Sets the action taken when the user closes the frame. Always specify JFrame.EXIT ON CLOSE.

Useful JFrame Constructors and Methods (Cont’d) Method Description void setIconImage (Icon image) Sets the icon displayed when the frame is minimized. void setLayout (LayoutManager layout) Sets the layout manager used to control how components are arranged when the frame is displayed. The default is the BorderLayout manager.

Useful JFrame Constructors and Methods (Cont’d) Method Description void setLocation (int x, int y) Sets the x and y position of the frame on-screen. The top-left corner of the screen is 0, 0. void setLocationRelativeTo (Component c) Centers the frame on-screen if the parameter is null.

Useful JFrame Constructors and Methods (Cont’d) Method Description void setResizeable (boolean value) Sets whether or not the size of the frame can be changed by the user. The default setting is true (the frame can be resized).

Useful JFrame Constructors and Methods (Cont’d) Method Description void setSize (int width, int height) Sets the size of the frame to the specified width and height. void setJMenuBar(JMenuBarMenu) Sets the menu for this frame.

Using the JPanel Class ■ A panel is a type of container that's designed to hold a group of components so they can be displayed on a frame. The normal way to display a group of controls such as text fields, labels, buttons, and other GUI widgets is to add those controls to a panel, and then add the panel to the frame. ■ You can bypass the panel and add the controls directly to the frame if you want, but using a separate panel to hold the frames control is almost always a good idea.

Useful JPanel Constructors and Methods Constructor Description JPanel () Creates a new panel. JPanel (boolean isDoubleBuffered) Creates a new panel. If the parameter is true, the panel uses a technique called double-buffering.

Useful JPanel Constructors and Methods (Cont’d) Constructor Description JPanel (LayoutManager layout) Creates a new panel with the specified layout manager. The default layout manager is FIowLayout.

Useful JPanel Constructors and Methods (Cont’d) Method Description void add (Component c) Adds the specified component to the panel. void remove (Component c) Removes the specified component from the panel.

Useful JPanel Constructors and Methods (Cont’d) Method Description void setLayout (LayoutManager layout) Sets the layout manager used to control how components are arranged when the panel is displayed. The default is the FIowLayout manager.

Useful JPanel Constructors and Methods (Cont’d) Method Description void setLocation (int x, int y) Sets the x and y position of the frame-screen. The top-left corner of the screen is 0, 0.

Useful JPanel Constructors and Methods (Cont’d) Method Description void setSize (int width, int height) Sets the size of the frame to the specified width and height. void setToolTipText (String text) Sets the tooltip text that's displayed if the user rests the mouse over an empty part of the panel.

Using Labels ■ A label is a component that simply displays text. Labels are used for a variety of purposes: to display captions for other controls such as text fields or combo boxes, to display informational messages, or to show the results of a calculation or a database lookup.

Using Labels ■ A label can also display an image, or it can display both an image and some text. And you have complete control over the appearance of the text. ■ You can specify the font, size, whether the text is bold, italic, or underlined, what color the text is displayed as, and so on.

Useful JLabels Constructors and Methods Constructor Description JLabel ( ) Creates a new label with no initial text. Method Description String getText ( ) Returns the text displayed by the label. void setText (String text) Sets the text displayed by the label.

Useful JLabels Constructors and Methods (Cont’d) Method Description void setToolTipText (String text) Sets the tooltip text that's displayed if the user rests the mouse over the label for a few moments. void setVisible (boolean value) Shows or hides the label.

Creating Buttons ■ Next to labels, the Swing component used most is the JButton component which creates a button the user can click. ■ The constructors of the JButton class are similar to the constructors for the JLabel class. You can either create an empty button or a button with text.

Useful JPanels Constructors and Methods Constructor Description JButton ( ) Creates a new button with no initial text. JButton (String text) Creates a new button with the specified text.

Useful JPanels Constructors and Methods (Cont’d) Method Description doClick ( ) Triggers an action event for the button as if the user clicked it. String getText () Returns the text displayed b the button.

Useful JPanels Constructors and Methods (Cont’d) Method Description void setBorderPainted (boolean value) Shows or hides the button's border. The default setting is true (the border is shown). void setContentAreaFilled (boolean value) Specifies whether or not the button's background should be filled or left empty. The default setting is true (the background is filled in).

Useful JPanels Constructors and Methods (Cont’d) Method Description void setContentAreaFilled (boolean value) Specifies whether or not the button's background should be filled or left empty. The default setting is true (the background is filled in). void setEnabled (boolean value) Enables or disables the button. The default setting is true (enabled).

Useful JPanels Constructors and Methods (Cont’d) Method Description void setRolloverEnabled (boolean value) Enables or disables the rollover effect, which causes the border to get thicker when the mouse moves over the button. The default setting is true (rollover effect enabled).

Useful JPanels Constructors and Methods (Cont’d) Method Description void setText (String text) Sets the text displayed by the button. void setToolTipText (String text) Sets the tooltip text that's displayed if the user lets the mouse rest over the button. void setVisible (boolean value) Shows or hides the button. The default setting is true (the button is visible).

Advanced java programming - awt packages

More Related Content

Similar to Advanced java programming - awt packages

Recently uploaded

Advanced java programming - awt packages