java 图形用户界面示例

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

import javax.swing.JButton;
public class AppGraIO {
	public static void main(String args[])
	{
		new AppFrame();
	}
}
class AppFrame extends JFrame
{
	JTextField in=new JTextField(10);
	JButton btn = new JButton("求平方");
	JLabel out = new JLabel("用于显示结果的标签");
	public AppFrame()
	{
		setLayout( new FlowLayout());
		getContentPane().add(  in );
		getContentPane().add( btn );
		getContentPane().add( out );
		btn.addActionListener( new BtnActionAdapter() );
//		btn.addActionListener(e->{
//			String s =  in.getText();
//			double d = Double.parseDouble( s );
//			double sq = Math.sqrt(d);
//			out.setText(d + "的平方根是：" +sq);
//		});
		setSize( 400,100);
		setDefaultCloseOperation(DISPOSE_ON_CLOSE);
		setVisible(true);
	}

   class BtnActionAdapter implements ActionListener
   {
	   public void actionPerformed( ActionEvent e)
	   {
		   String s= in.getText();
		   double d = Double.parseDouble(s);
		   double sq = d * d;
		   out.setText(d + "的平方是："+sq);
	   }
   }
	
}