java.lang.Object
--java.awt.Component
--java.awt.Container
--javax.swing.JComponent
--javax.swing.AbstractButton
--javax.swing.JMenuItem
--javax.swing.JRadioButtonMenuItem
与JCheckBoxMenuItem相同,JRadioButtonItem也是继承JMenuItem,因此JRadioButtonMenuItem也具备JMenuItem的许多特性.而 JRadioButtonMenuItem和JCheckBoxMenuItem一样也是一种特殊的JMenuItem.我们在前面也介绍过JRadioButton组件,而 JRadioButtonMenuItem是专用在MenuItem上.我们来看看JRadioButtonMenuItem的构造方法,如下表:
由一表可以看出JRadioButtonMenuItem的构造方式与JCheckBoxMenuItem构造方式几乎相同,而且和JCheckBoxMenuItem的构造方 式一样都是比JMenuItem的构造方式多了设置选择状况的构造方式,设置选择状态就是决定是否要将构造好的JRadioButtonMenuItem 设置为默认值.我们来看下面这个范例:
import javax.swing.*;
import java.awt.event.*;
public class JRadioButtonMenuItem1 extends JFrame implements ActionListener {
JTextArea theArea = null;
public JRadioButtonMenuItem1() {
super("JRadioButtonMenuItem1");
theArea = new JTextArea();
theArea.setEditable(false);
getContentPane().add(new JScrollPane(theArea));
JMenuBar MBar = new JMenuBar();
MBar.setOpaque(true);
JMenu mfile = buildFileMenu();
JMenu mstyle = buildStyleMenu();
MBar.add(mfile);
MBar.add(mstyle);
setJMenuBar(MBar);
}// end of JRadioButtonMenuItem1()
public JMenu buildFileMenu() {
JMenu thefile = new JMenu("File");
thefile.setMnemonic('F');
JMenuItem newf = new JMenuItem("New", new ImageIcon("icons/new24.gif"));
JMenuItem open = new JMenuItem("Open",
new ImageIcon("icons/open24.gif"));
JMenuItem close = new JMenuItem("Close", new ImageIcon(
"icons/close24.gif"));
JMenuItem quit = new JMenuItem("Exit",
new ImageIcon("icons/exit24.gif"));
newf.setMnemonic('N');
open.setMnemonic('O');
close.setMnemonic('L');
quit.setMnemonic('X');
newf.setAccelerator(KeyStroke.getKeyStroke('N',
java.awt.Event.CTRL_MASK, false));
open.setAccelerator(KeyStroke.getKeyStroke('O',
java.awt.Event.CTRL_MASK, false));
close.setAccelerator(KeyStroke.getKeyStroke('L',
java.awt.Event.CTRL_MASK, false));
quit.setAccelerator(KeyStroke.getKeyStroke('X',
java.awt.Event.CTRL_MASK, false));
newf.addActionListener(this);
open.addActionListener(this);
close.addActionListener(this);
quit.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.exit(0);
}
});
thefile.add(newf);
thefile.add(open);
thefile.add(close);
thefile.addSeparator();
thefile.add(quit);
return thefile;
}// end of buildFileMenu()
public JMenu buildStyleMenu() {
JMenu style = new JMenu("Style");
style.setMnemonic('S');
JRadioButtonMenuItem Left = new JRadioButtonMenuItem("Left",
new ImageIcon("icons/left24.gif"));
JRadioButtonMenuItem Center = new JRadioButtonMenuItem("Center",
new ImageIcon("icons/center24.gif"));
JRadioButtonMenuItem Right = new JRadioButtonMenuItem("Right",
new ImageIcon("icons/right24.gif"));
JRadioButtonMenuItem Justify = new JRadioButtonMenuItem("Justify",
new ImageIcon("icons/justify24.gif"));
Left.setMnemonic('L');
Center.setMnemonic('E');
Right.setMnemonic('R');
Justify.setMnemonic('J');
Left.setAccelerator(KeyStroke.getKeyStroke('L',
java.awt.Event.SHIFT_MASK, false));
Center.setAccelerator(KeyStroke.getKeyStroke('E',
java.awt.Event.SHIFT_MASK, false));
Right.setAccelerator(KeyStroke.getKeyStroke('R',
java.awt.Event.SHIFT_MASK, false));
Justify.setAccelerator(KeyStroke.getKeyStroke('J',
java.awt.Event.SHIFT_MASK, false));
Left.addActionListener(this);
Center.addActionListener(this);
Right.addActionListener(this);
Justify.addActionListener(this);
style.add(Left);
style.add(Center);
style.add(Right);
style.add(Justify);
return style;
}// end of buildStyleMenu()
public void actionPerformed(ActionEvent ae) {
try {
theArea.append("* action '" + ae.getActionCommand()
+ "' performed. *\n");
} catch (Exception e) {
System.out.println("actionPerformed Exception:" + e);
}
}
public static void main(String[] args) {
JFrame F = new JRadioButtonMenuItem1();
F.setSize(400, 200);
F.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});// end of addWindowListener
F.setVisible(true);
} // end of main
}// end of class JRadioButtonMenuItem1
在这个范例中我们遇到了与JRadioButton同样的问题,那就是选项的单、复选的问题.一般来说RadioButton组件是用来做单选 的情况时使用,而CheckBox则是多为复选情况时使用.那么我们该怎么来解决这个问题呢?还记得我们介绍JRadioButton时的解决方式 吗?没错,就是要利用ButtonGroup类来处理.我们在JRadioButtonMenuItem1.java的buildStyleMenu()方法中加下下列五行:
ButtonGroup bg=new ButtonGroup();
bg.add(Left);
bg.add(Center);
bg.add(Right);
bg.add(Justify);
运行程序我们可看到加入ButtonGroup后的JRadioButtonMenuItem变成只能被单选的菜单.