} } } } // vs...

Odnośniki

Smutek to uczucie, jak gdyby się tonęło, jak gdyby grzebano cię w ziemi.

an individual class for each item:
class IL4 implements ItemListener {
public void itemStateChanged(ItemEvent e) {
t.setText("Radio button four");
}
}
class IL5 implements ItemListener {
public void itemStateChanged(ItemEvent e) {
t.setText("Radio button five");
}
}
class IL6 implements ItemListener {
public void itemStateChanged(ItemEvent e) {
t.setText("Radio button six");
}
}
public static void main(String[] args) {
RadioCheckNew applet = new RadioCheckNew();
Frame aFrame = new Frame("RadioCheckNew");
aFrame.addWindowListener(
new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
aFrame.add(applet, BorderLayout.CENTER);
aFrame.setSize(300,200);
applet.init();
applet.start();
aFrame.setVisible(true);
}
} ///:~
ILCheck has the advantage that it automatically adapts when you add or subtract Checkboxes. Of course, you can use this with radio buttons as well. It should be used, however, only when your logic is general enough to support this approach. Otherwise you’ll end up with a cascaded if statement, a sure sign that you should revert to using independent listener classes.
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Drop-down lists
Drop-down lists (Choice) in Java 1.1 also use ItemListeners to notify you when a choice has changed:
//: ChoiceNew.java
// Drop-down lists with Java 1.1
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class ChoiceNew extends Applet {
String[] description = { "Ebullient", "Obtuse",
"Recalcitrant", "Brilliant", "Somnescent",
"Timorous", "Florid", "Putrescent" };
TextField t = new TextField(100);
Choice c = new Choice();
Button b = new Button("Add items");
int count = 0;
public void init() {
t.setEditable(false);
for(int i = 0; i < 4; i++)
c.addItem(description[count++]);
add(t);
add(c);
add(b);
c.addItemListener(new CL());
b.addActionListener(new BL());
}
class CL implements ItemListener {
public void itemStateChanged(ItemEvent e) {
t.setText("index: " + c.getSelectedIndex()
+ " " + e.toString());
}
}
class BL implements ActionListener {
public void actionPerformed(ActionEvent e) {
if(count < description.length)
c.addItem(description[count++]);
}
}
public static void main(String[] args) {
ChoiceNew applet = new ChoiceNew();
Frame aFrame = new Frame("ChoiceNew");
aFrame.addWindowListener(
new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
aFrame.add(applet, BorderLayout.CENTER);
aFrame.setSize(750,100);
applet.init();
applet.start();
Chapter 13: Creating Windows & Applets
525
aFrame.setVisible(true);
}
} ///:~
Nothing else here is particularly new (except that Java 1.1 has significantly fewer bugs in the UI classes).
Lists
You’ll recall that one of the problems with the Java 1.0 List design is that it took extra work to make it do what you’d expect: react to a single click on one of the list elements. Java 1.1
has solved this problem:
//: ListNew.java
// Java 1.1 Lists are easier to use
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class ListNew extends Applet {
String[] flavors = { "Chocolate", "Strawberry",
"Vanilla Fudge Swirl", "Mint Chip",
"Mocha Almond Fudge", "Rum Raisin",
"Praline Cream", "Mud Pie" };
// Show 6 items, allow multiple selection:
List lst = new List(6, true);
TextArea t = new TextArea(flavors.length, 30);
Button b = new Button("test");
int count = 0;
public void init() {
t.setEditable(false);
for(int i = 0; i < 4; i++)
lst.addItem(flavors[count++]);
add(t);
add(lst);
add(b);
lst.addItemListener(new LL());
b.addActionListener(new BL());
}
class LL implements ItemListener {
public void itemStateChanged(ItemEvent e) {
t.setText("");
String[] items = lst.getSelectedItems();
for(int i = 0; i < items.length; i++)
t.append(items[i] + "\n");
}
}
class BL implements ActionListener {
public void actionPerformed(ActionEvent e) {
if(count < flavors.length)
lst.addItem(flavors[count++], 0);
}
}
public static void main(String[] args) {
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ListNew applet = new ListNew();
Frame aFrame = new Frame("ListNew");
aFrame.addWindowListener(
new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
aFrame.add(applet, BorderLayout.CENTER);
aFrame.setSize(300,200);
applet.init();
applet.start();
aFrame.setVisible(true);
}
} ///:~
You can see that no extra logic is required to support a single click on a list item. You just attach a listener like you do everywhere else.
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