复选框组件例13.12程序运行默认不显示内容问题解决方法

复选框组件例13.12程序运行默认不显示内容问题解决方法

package com.txw;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class CheckBoxTest extends JFrame {
	
	
	
    private static final long serialVersionUID=1L;
    
    private JPanel panel1=new JPanel();
    private JPanel panel2=new JPanel();
    private JTextArea jt=new JTextArea(8,20);
    private JCheckBox jc1=new JCheckBox("check1");
    private JCheckBox jc2=new JCheckBox("check2");
    private JCheckBox jc3=new JCheckBox("check3");
    public CheckBoxTest(){
    	Container c=getContentPane();
    	/*setSize(600,400); //4行代码位置不对，导致运行程序时内容不显示，
    	setVisible(true);
    	setTitle("check box usage");*/
    	//setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    	c.setLayout(new BorderLayout());
    	
    //
    	c.add(panel1, BorderLayout.NORTH);
    	final JScrollPane scrollPane=new JScrollPane(jt);
    	panel1.add(scrollPane);
    	
    	//
    	c.add(panel2, BorderLayout.SOUTH);
    	panel2.add(jc1);
    	jc1.addActionListener(new ActionListener(){
    		public void actionPerformed(ActionEvent e){
    			if(jc1.isSelected())
    			jt.append("check box1 is choosed\n");
    		}
    	});
    	
    	//
    	panel2.add(jc2);
    	jc2.addActionListener(new ActionListener(){
    		public void actionPerformed(ActionEvent e){
    			if(jc2.isSelected())
    				jt.append("check box2 is choosed\n");
    		}
    	});
    	panel2.add(jc3);
    	jc3.addActionListener(new ActionListener(){
    		public void actionPerformed(ActionEvent e){
    			if(jc3.isSelected())
    				jt.append("check box3 is choosed\n");
    		}
    	});
    	
    	setSize(600,400); //放置在这个位置
    	setVisible(true);//放置在这个位置
    	setTitle("check box usage");//放置在这个位置
    	setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);//放置在这个位置
    }
	public static void main(String[] args) {
		// TODO Auto-generated method stub
    new CheckBoxTest();
	}

}
package