初学JAVA，笔记：

package windows;

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

class WindowFlow extends JFrame implements ActionListener{

private static final long serialVersionUID = 1L;

JTextField text1,text2;

WindowFlow(String s){

super(s);

FlowLayout flow=new FlowLayout();

setLayout(flow);

text1=new JTextField(10);

text2=new JTextField(10);

text2.setEditable(false);

add(text1);

add(text2);

text1.addActionListener(this);

setBounds(100,100,330,70);

validate();

setVisible(true);

setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

}

public void actionPerformed(ActionEvent e){

if(e.getSource()==text1){

int n=0,m=0;

try{

n=Integer.parseInt(text1.getText());

m=n*n;

text2.setText(n+"的平方是："+m);

}

catch(Exception ee){

text2.setText("请输入数字字符！");

text1.setText(null);

}

}

}

}

public class JButtonE {

public static void main(String args[]){

new WindowFlow("JAVA控件示例程序");

}

}