import java.awt.*;
import java.awt.event.*;
import javax.swing.*;/**包含JFrame*/
public class AppGraphInOut {
    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("用于显示平方结果的标签");
    public AppFrame()
    {
        setLayout(new FlowLayout());
        getContentPane().add(in);
        getContentPane().add(btn);
        getContentPane().add(out);
        btn.addActionListener(new BtnActionAdapter());
        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);
        }
    }
}