jtextarea4.java

《精通Java Swing程序设计S》这本书所附带的JAVA程序写得很漂亮,都是SWING的实例子,很适合初学者。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.undo.*;
import javax.swing.event.*;

public class JTextArea4 extends JFrame implements UndoableEditListener{

    private UndoableEdit edit;
    private JTextArea    jta;
    private JTextArea    message;
    private JMenuItem    undoitem;
    private JMenuItem    redoitem;
   
    public JTextArea4(){
    	
    	super("JTextArea4");
    	jta = new JTextArea();
    	jta.getDocument().addUndoableEditListener(this);

        message = new JTextArea();
        message.setEditable(false);

        JPanel p1 = new JPanel();
        p1.setLayout(new GridLayout(1,1));
        p1.setBorder(BorderFactory.createTitledBorder("Edit Area"));  
        p1.add(new JScrollPane(jta));

        JPanel p2 = new JPanel();
        p2.setLayout(new GridLayout(1,1));
        p2.setBorder(BorderFactory.createTitledBorder("Message"));  
        p2.add(new JScrollPane(message));        
        
    	getContentPane().setLayout(new GridLayout(2,1));
    	getContentPane().add(p1);
    	getContentPane().add(p2);
    	
    	JMenuBar bar  = new JMenuBar();
    	JMenu theMenu = new JMenu("Edit");
    	undoitem = new JMenuItem("Undo");
    	redoitem = new JMenuItem("Redo");
    	theMenu.add(undoitem);
    	theMenu.add(redoitem);
    	bar.add(theMenu);
    	updateMenuItem();
    	
    	setJMenuBar(bar);
    	setSize(300,300);
    	
    	undoitem.addActionListener(new ActionListener(){
    		public void actionPerformed(ActionEvent ev){
    			edit.undo();
    			updateMenuItem();
    			message.append("- Undo -\n");
    		}	
    	});

    	redoitem.addActionListener(new ActionListener(){
    		public void actionPerformed(ActionEvent ev){
    			edit.redo();
    			updateMenuItem();
    			message.append("- Redo -\n");
    		}	
    	});    	
    }//end of JTextArea4()

    public void undoableEditHappened(UndoableEditEvent ev){
    	StringBuffer buf = new StringBuffer(200);
    	edit = ev.getEdit();
    	buf.append("undoableEdit:");
    	buf.append(edit.getPresentationName());
    	buf.append("\n");
    	message.append(buf.toString());
    	updateMenuItem();
    }//end of undoableEditHappened()

    public void updateMenuItem(){
    	
    	if (edit != null){
		  undoitem.setEnabled(edit.canUndo());
		  redoitem.setEnabled(edit.canRedo());
		  undoitem.setText(edit.getUndoPresentationName());
		  redoitem.setText(edit.getRedoPresentationName());
	    }else{
		  undoitem.setEnabled(false);
	  	  redoitem.setEnabled(false);
		  undoitem.setText("Undo");
		  redoitem.setText("Redo");
	}
    }//end of updateMenu()

    public static void main(String args[])    {

    	JFrame f = new JTextArea4();
    	f.addWindowListener(new WindowAdapter() {            
    		public void windowClosing(WindowEvent e) {                    
    			System.exit(0);            
    		}        
    	});
    	f.show();
    }//end of main()
}//end of class JTextArea4