import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Area12 implements ActionListener{
	//JFrame.setDefaultLookAndFeelDecorated(true);
	JFrame computarea=new JFrame("圓面積計算器");
	JButton compute,clear;
	JTextField input,output;
	JLabel label1,label2;
	JPanel panel1,panel2,panel3;
	 Area12(){
		    compute=new JButton("計算");
		    clear=new JButton("清空");
		    input=new JTextField(20);
		    output=new JTextField(20);	     
		    output.setEditable(false);
		    label1=new JLabel("請輸入半徑:",JLabel.RIGHT);
		    label2=new JLabel("圓的面積為:",JLabel.RIGHT);
		    panel1=new JPanel();
		    panel2=new JPanel();
		    panel3=new JPanel();
		    compute.addActionListener(this);
		    clear.addActionListener(this);
		    compute.setActionCommand("compute");
		    clear.setActionCommand("clear");
	 }
	public void lanchFrame(){
		panel1.setLayout(new GridBagLayout());
		panel2.setLayout(new GridBagLayout());
		panel1.add(label1);
	    panel1.add(input);
	    panel2.add(label2);
	    panel2.add(output);
	    panel3.add(compute);
	    panel3.add(clear);
	    computarea.add(panel1,BorderLayout.NORTH);
	    computarea.add(panel2,BorderLayout.CENTER);
	    computarea.add(panel3,BorderLayout.SOUTH);
	    computarea.pack();
		computarea.setVisible(true);
		computarea.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
	}
	public void actionPerformed(ActionEvent e) {
		if("clear".equals(e.getActionCommand()))
		{
			input.setText("");
    		output.setText("");
		}
		else if("compute".equals(e.getActionCommand()))
		{
			double r=Double.parseDouble(input.getText());
	    	double area=Math.PI*r*r;
	    	output.setText(String.valueOf(area));
		}
	}
	  public static void main(String[] args) {		
		Area12 p=new Area12();
		p.lanchFrame();
	}
}