



More Events


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As you saw in the last lesson you can handle events in a variety of ways.
In fact we could make a four by two matrix representing our options:


Adapter Classes Listener Interfaces

Outer Classes this lesson this lesson

Classes next lesson next lesson

Inner Classes two lessons from now two lessons from now

Low-Level three lessons from now three lessons from now


For further information study these pages:
Java Event Model

Examples of six different approaches (EXCELLENT
EXAMPLES!)

Examples Using Inner Classes

Example Using Low Level Event Handling


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Java 1.1 Event Types, Listeners, and Listener Methods:



Event Class Listener Interface Listener Methods

ActionEvent ActionListener actionPerformed()

AdjustmentEvent AdjustmentListener adjustmentValueChanged()

ComponentEvent ComponentListener
componentHidden()
componentMoved()
componentResized()

componentShown()

ContainerEvent ContainerListener
componentAdded()
componentRemoved()

FocusEvent FocusListener
focusGained()
focusLost()

ItemEvent ItemListener itemStateChanged()

KeyEvent KeyListener keyPressed()
keyReleased()

keyTyped()

MouseEvent MouseListener
mouseClicked()
mouseEntered()
mouseExited()

mousePressed()
mouseReleased()

MouseMotionListener
mouseDragged()
mouseMoved()

TextEvent TextListener textValueChanged()

WindowEvent WindowListener
windowActivated()
windowClosed()
windowClosing()

windowDeactivated()
windowDeiconified()

windowIconified()
windowOpened()



Any Listener interface which provides more than one method has a corresponding
Adapter class. When you implement an interface you must provide definitions
for all of its methods. When you extend a class you only provide definitions
for the methods you wish to override. This is the advantage of using Adapter
classes: You only have to provide definitions for the methods you wish to 
use.

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Example One: External Class, Listener Interface, List Component:



import java.awt.*;
import java.applet.*;
import java.awt.event.*;

public class list extends Applet{
  List list;
  Label l;
  TextField t;

  public void init(){
    setBackground(Color.yellow);
    list = new List(4,false);
    list.addItem("Chicago Pansies");
    list.addItem("Denver Duds");
    list.addItem("Miami Fish");
    list.addItem("Boston Fartknockers");
    list.addItem("Pittsburgh Poodles");
    list.addItem("Los Angeles Smog");
    l=new Label("Pick A Winner");
    t=new TextField(30);
    list.addItemListener(new IL(this));
    add(l);
    add(list);
    add(t);
  }
}

class IL implements ItemListener{
  list L;

  IL(list el){
    L=el;
  }
  
  public void itemStateChanged(ItemEvent e){
    String s = L.list.getSelectedItem();
    L.t.setText("The winner is: "+s);
  }
}
//<applet code=list.class height=120 width=300></applet>




Notice the constructor for the IL class. It takes an instance of the list
class as an argument. This is so items from the list class can be accessed
within the IL class. This would not be necessary if we had used inner classes.


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Example Two: External Class, Adapter Class, Scrollbar Component:


import java.awt.*;
import java.applet.*;
import java.awt.event.*;

public class scroll extends Applet{
  Scrollbar sb;
  Label l;
  TextField t;

  public void init(){
    setBackground(Color.cyan);
    setLayout(new GridLayout(3,1));
    l= new Label("Cans Of Soda A Week:");
    sb=new Scrollbar(Scrollbar.HORIZONTAL, 3, 0, 0, 100);
    sb.addAdjustmentListener(new AL(this));
    sb.setBackground(Color.yellow);
    t=new TextField("How many cans do you drink in a week?");
    add(l);
    add(sb);
    add(t);
  }
}

class AL implements AdjustmentListener{
  scroll S;

  AL(scroll s){
    S=s;
  }

  public void adjustmentValueChanged(AdjustmentEvent e){
    int v=S.sb.getValue();
    S.t.setText("Cans per week: "+v);
  }
}
//<applet code=scroll.class height=200 width=300></applet>





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Thinking In Java:

Read the following sections from chapter thirteen: "Check Boxes and Radio
Buttons," "Drop-down Lists," "Lists," and "Menus."



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Assignment: Recreate the following applet:




You will need to use panels to recreate the exact layout... but you don't
have to be perfect, but it will still have to be pretty darn good.

	Adapter Classes	Listener Interfaces
Outer Classes	this lesson	this lesson
Classes	next lesson	next lesson
Inner Classes	two lessons from now	two lessons from now
Low-Level	three lessons from now	three lessons from now

Event Class	Listener Interface	Listener Methods
ActionEvent	ActionListener	actionPerformed()
AdjustmentEvent	AdjustmentListener	adjustmentValueChanged()
ComponentEvent	ComponentListener	componentHidden() componentMoved() componentResized() componentShown()
ContainerEvent	ContainerListener	componentAdded() componentRemoved()
FocusEvent	FocusListener	focusGained() focusLost()
ItemEvent	ItemListener	itemStateChanged()
KeyEvent	KeyListener	keyPressed() keyReleased() keyTyped()
MouseEvent	MouseListener	mouseClicked() mouseEntered() mouseExited() mousePressed() mouseReleased()
MouseEvent	MouseMotionListener	mouseDragged() mouseMoved()
TextEvent	TextListener	textValueChanged()
WindowEvent	WindowListener	windowActivated() windowClosed() windowClosing() windowDeactivated() windowDeiconified() windowIconified() windowOpened()