13 2 Event Handling and Layout Managers

8/14/2019 13 2 Event Handling and Layout Managers

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1Java

Event Handling and Layout

Managers


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3Java

Null Layout Manager23

Constructors and Methods22

GridLayout21


BorderLayout19


FlowLayout17

Layout Manager Classes16MouseListener and MouseEvent15

ItemListener and ItemEvent14

WindowAdapter13

Adapters12

Contents


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4Java

Know

How the Delegation event model works

Listeners and Adapter classes

Layout Managers


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5Java

Be able to

Implement Listeners and Adapter classes

Use Layout Managers effectively


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6Java

Club where sports event happen

Inter ClubSports

Event

I must register

myself as a club

member so that

when an event

happens, the club

informs me.

Annual Sports

EventI run

I run

Anu

Raj


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7Java

Sports club where sports event happen

Inter ClubSports

Event

Annual Sports

EventI run

I run

Annual eventhappening .

Please run.

Anu

Raj


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8Java

Source object

Inter ClubSports

Event

Annual Sports

Event

Listeners objects

Event object

Java terminology

Anu

Raj


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9Java

Source has list of athletes objects

(Anu, Raj). Source will ensure that

they have run() method. When event

happens source will call anu.run()and raj.run()

Annual Sports

Event

Register me. I

have

implemented

Running

Java way of handling events

Anu

Raj

Inviting members whocan run.(Only objectswhich implements

Running (run()method))


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10Java

The Delegation Event Model

Source(Ex. JButton)

Listener (Ex. JFrame)

2. Generates events(user clicks)

Event

object

3. Calls a method on the

Listener and sends event object

1. Registers itself to receive events


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11Java

Event types

Low level events

Examples:

Pressing keyboard buttons

Mouse clicks

Semantic events:

Examples:

Button click

Selecting an item in the list


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Low level events

MouseEvent

KeyEvent

Generated by all the components.


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13Java

JButton, JMenuItem, JRadioButton,JCheckbox, JTextField:

java.awt.event.ActionEvent JTextField ,JTextArea, JPasswordField:

java.awt.event.InputMethodEvent

JTabbedPanejavax.swing.event.ChangeEvent

JFrame:

java.awt.event.WindowEvent JCombo:

java.awt.event.ItemEvent JList:

javax.swing.event.ListSelectionEvent

Semantic events


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EventObject

Root class for all event objects

Object getSource()

A method in EventObject class.

Which returns us the source object on which the

Event initially occurred.


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Listeners XxxListener is an interface any source would

implement if it is interested in a particularXxxevent.

A source generating an XxxEvent would allowonly those components to register with it whohave implemented XxxListener.

XxxListener will have one or more methodswhich sources interested in the vent wouldimplement.

When event occurs the source will call themethod of XxxListener for all the componentswho have registered with it.


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16Java

Listeners Interfaces

corresponding to each Event

object

ActionEvent ActionListener

InputMethodEvent InputMethodListener ChangeEvent ChangeListener

WindowEvent WindowListener

ItemEvent ItemListener ListSelectionEvent ListSelectionListener

java.awt.event

javax.swing.event


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Registering the listener with

the source

source.addXxxListener(XxxListener t)

where

source is any Component

Xxx: could be any one of the Listenermentioned in the previous slide


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18Java

What are we going to look at?

We will look at only the below

listed Events. The others are very

similar. You can get all the

information about Listenermethods and Event methods from

the API.

1.ActionListener2.WindowListener

3.ItemListener

4.MouseListener


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19Java

ActionListener andActionEvent

Source that generates ActionEvent:

Button object is clicked

MenuItem object is selected

List object is double clicked

Listener: ActionListener

public void actionPerformed(ActionEvent e)

Useful ActionEvent method: public String getActionCommand()


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Example

On clicking2. Red - the panelbecomes Red.

3. Green - the panelbecomes Green

4. Blue - the panelbecomes Blue.


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21Java

import javax.swing.*;

import java.awt.event.*;

import java.awt.Color;public class ColorFrame extends JFrameimplements ActionListener{

JPanel panel =new JPanel();

public ColorFrame (){

super("Simple Frame With Color Button");

setSize(300,300);

setVisible(true);

JButton red=new JButton("Red");

JButton green=new JButton("Green");

JButton blue=new JButton("Blue");

Creating buttonsExample 1


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panel.add(red);

panel.add(blue);

panel.add(green);getContentPane().add(panel);

red.addActionListener(this);

green.addActionListener(this);

blue.addActionListener(this);

}public void actionPerformed(

ActionEvent e){

if(e.getActionCommand().equals("Red"))

panel.setBackground(Color.red);

Adding buttons to thepanel and panel to theframe.

Register the current object with the buttons


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23Java

if(e.getActionCommand().equals("Green"))

panel.setBackground(Color.green);

if(e.getActionCommand().equals("Blue"))

panel.setBackground(Color.blue);

}public static void main(String str[]){

new ColorFrame();

}}


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24Java

If you dont mind can we handle the frame

close event. I am tried of pressing control-C.

Sure!


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25Java

WindowListener and WindowEvent Source And Event: Frame close,open, minimize,

maximize

Listener: WindowListener

void windowClosing(WindowEvent e)

void windowClosed(WindowEvent e)

void windowOpened(WindowEvent e)

void windowDeiconified(WindowEvent e)

void windowIconified(WindowEvent e)

void windowActivated(WindowEvent e)

void windowDeactivated(WindowEvent e)


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26Java

You mean I will have to implement 7 methods

to handle window closing event ! I think I amok with control-C.

Surely not. Java creators

knew about the

programmers reaction tothis. They created Adapter

classes for rescue.


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Adapters

Adapter classes are useful when we want to

override only methods we are interested in.

Adapter classes implement the the listener

interfaces and provide empty implementation

for all the methods defined in the interface.


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29Java

I dont understand how Adapterswill help. My frame class already

extends Frame. So my frame classcannot inherit from Adapter noMULTIPLE INHERITANCE in Java.

If we implement using WindowListener, thesource and the listener both are the sameobject. With Adapters, we delegate the eventhandling to WindowAdapter object.So wedont have to inherit from Adapter class.


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//import statements

public class ColorFrame extends Frameimplements ActionListener{

WindowAdapter win;

public ColorFrame(){

super("Simple Frame With Menu");

win= new WindowAdapter(){Example 2


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Oh it has become so incredibly easyand the code also looks very

professional. I use to hate inner classbut I think now I have started liking it.

Having said all this about adaptersjust remember that we haveAdapter classes only for those

Listener interfaces which havemore than one method. (It makesperfect sense, right!)


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33Java

ItemListener and ItemEvent

Source And Event: Checkbox or a List item is

clicked or a Choice is selected or deselected.

Listener: ItemListener

public voiditemStateChanged(ItemEvent e)

Interesting ItemEvent method

int getStateChange()ItemEvent.SELECTED

ItemEvent.DESELECTED


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34Java

import java.awt.*;


import javax.swing.*;public class ColorAWT extends JFrame

implementsItemListener{

JComboBox colors;

JPanel panel= new JPanel();

ColorAWT() {

super("Item listener");

colors=new JComboBox();

colors.addItem("Red");

colors.addItem("Green");

Adding items intothe combo box

Example 3


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colors.addItem("Blue");

panel.add(colors);

getContentPane().add(panel);setSize(200,200);

setVisible(true);

colors.addItemListener(this);}

public void itemStateChanged(ItemEvent ie

{

String

color=(String)colors.getSelectedItem();

if(color.equals("Red"))

panel.setBackground(Color.RED);


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37Java

MouseListener and MouseEvent

Source and event: Mouse button pressed,released etc.

Listener: MouseListener

void mouseClicked(MouseEvent e)

void mouseEntered(MouseEvent e)

void mouseExited(MouseEvent e)

void mousePressed(MouseEvent e)

void mouseReleased(MouseEvent e)

MouseEvent methods:

public int getX() ,public int getY()


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Exactly!

Lets us draw lines on theframe. Each click of the

mouse will determine the

start point and the end point

of the line.

We certainly can use MouseAdapter

instead of typing this long list of methods

of MouseListerner, right!


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import java.awt.*;


Import javax.swing.*;

public class DrawLines extends JFrame {

int x1=0;

int y1=0;

int x2,y2;

boolean firstPoint=true;

DrawLines() {

super("Mouse Listener");setSize(600,600);

setVisible(true);

setBackground(Color.white);

Example 4


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MouseAdapter ma= new MouseAdapter(){

public void mousePressed(MouseEvent me)

{

if(firstPoint)

{ x1=me.getX();y1=me.getY()

;

firstPoint=false; }

x2=me.getX();

y2=me.getY();

draw(); }};

this.addMouseListener(ma);


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43Java

FlowLayout

A flow layout arranges components one afteranother from left to right, top to bottom. The flowdirection can also be changed to right to left.

The alignment can be either left, right centered.

By default it is centered. All the examples for the applet that we have seen

so far arranges the components in the flowlayout.


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Constructors and Methods

FlowLayout()

FlowLayout(int align)

FlowLayout(int align,int hgap,int vgap)

Getters and setter for

alignment

hgap

vgap

FlowLayout.CENTERFlowLayout.LEFT

FlowLayout.RIGHT

Horizontal gap and Vertical gap


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BorderLayout

The border layout divides the containers area intonorth, south, east, west and center.


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BorderLayout()

BorderLayout(int hgap, int vgap)

Setters and getters for

hgap and vgap


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import java.awt.*;

import java.awt.event.*;public class BorderExample extends JFrame

implements ActionListener{

JPanel colorPanel= new JPanel();

public static void main(String s[]){new BorderExample ();}

BorderExample() {

JPanel buttonPanel= new JPanel();

colorPanel.setBackground(Color.white);

Example 5


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setVisible(true);

setSize(300,100);

JButton red = new JButton("Red", new

ImageIcon("red.GIF"));

JButton green = new JButton("Green",new

ImageIcon("green.GIF"));JButton blue = new JButton("Blue",new

ImageIcon("blue.GIF"));

buttonPanel.add(red);

buttonPanel.add(green);buttonPanel.add(blue);


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getContentPane().add(buttonPanel,BorderLayout.NORTH);

getContentPane().add(colorPanel,

BorderLayout.CENTER);

red.addActionListener(this);

green.addActionListener(this);

blue.addActionListener(this);validate();

}


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G idL t


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GridLayout

This layout manager lays out a container'scomponents in a rectangular grid specified by

rows and columns in the constructor.

The entire area of the container is divided into

grid of equal sizes.

We change our Login

form that we createdin swing chapter toproper format.


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GridLayout()

GridLayout(int rows, int cols)

GridLayout(int rows, int cols,int hgap,

int vgap)Setters and getters for

hgap,vgap, rows and columns


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3 rows and 2 columns:GridLayout(3,2))


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import java.awt.*;

public class TestJFC extends JFrame {

public static void main(String s[]) {

new TestJFC();}

TestJFC() {

setVisible(true);setSize(300,120);

JPanel p= new JPanel();

p.setBackground(Color.white);

p.setLayout(new GridLayout(3,2));p.setBorder(BorderFactory.createMatteBo

rder(-1,-1,-1,-1,newImageIcon("bullet.gif")));

p.add(new JLabel("Login"));

Example 6


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JTextField login= new JTextField(10);

p.add(login);

p.add(new JLabel("Password"));

JPasswordField pass= newJPasswordField(10);

p.add(pass);

Stringroles[]={"Student","Teacher","HOD","Management"};

p.add(new JLabel("Role"));

JComboBox role= new JComboBox(roles);

p.add(role);

getContentPane().add(p);

validate();}}


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56Java

There are many more layout

managers. But if you are not

happy with any, then you canlayout the components as you

wish by setting the layout

manager to null.

What if I want to layout components and I

have no layout managers that will layout

in the way I want.


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public class BoundsDemo extends JFrame{

public BoundsDemo(){

super("Boundslayout");

setSize(350,200);

setVisible(true);

getContentPane().setLayout(null);JLabel lLogin=new JLabel("Login:");

JTextField login = new JTextField(20);

JLabel lPassword=new

JLabel("Password:");JPasswordField password = new

JPasswordField(20);

JButton b= new JButton("Submit");

Example 7


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lLogin.setBounds(30,30,100,15);

login.setBounds(150,30,100,20);

lPassword.setBounds(30,80,100,20);password.setBounds(150,80,100,20);

b.setBounds(150,150,100,20);

getContentPane().add(lLogin);

getContentPane().add(login);

getContentPane().add(lPassword);

getContentPane().add(password);

getContentPane().add(b);

repaint();

}


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public static void main(String str[]){

new BoundsDemo();}

}

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13 2 Event Handling and Layout Managers