请依次输入一元二次方程的三个系数，并点击计算显示实根

[java]代码库

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

public class Chp13_1 extends JFrame{

	private JButton jisuan;
	private JPanel panel1,panel2,panel3,panel4;
	private JTextField field1,field2,field3;
	private JLabel label1,label2,label3,label4;
	private JTextArea area;
	private Container container;
	
	Chp13_1(){
	
		super("计算一元二次方程的根");

		container = getContentPane();
		container.setLayout(new FlowLayout());
		
		label4 = new JLabel("请依次输入一元二次方程的三个系数，并点击计算显示实根");
		container.add(label4);
		
		panel1 = new JPanel();
		label1 = new JLabel("系数a");
		field1 = new JTextField(10);
		panel1.add(label1);
		panel1.add(field1);
		
		panel2 = new JPanel();
		label2 = new JLabel("系数b");
		field2 = new JTextField(10);
		panel2.add(label2);
		panel2.add(field2);
		
		panel3 = new JPanel();
		label3 = new JLabel("系数c");
		field3 = new JTextField(10);
		panel3.add(label3);
		panel3.add(field3);
		
		panel4 = new JPanel();
		panel4.setLayout(new GridLayout(1,3,1,2));
		panel4.add(panel1);
		panel4.add(panel2);
		panel4.add(panel3);
		container.add(panel4);
					
		jisuan = new JButton("计算");
		jisuan.addActionListener(
			new ActionListener(){			
				public void actionPerformed(ActionEvent event) {
					
					double a = Double.parseDouble(field1.getText());
					double b = Double.parseDouble(field2.getText());
					double c = Double.parseDouble(field3.getText());
					
					double deerta = b*b-4*a*c;
								
					if(deerta < 0){
						area.setText("无实根");
					}else {
						
						double x1 = (Math.sqrt(deerta)-b)/(2*a);
						double x2 = (-Math.sqrt(deerta)-b)/(2*a);
						
						area.setText("实根1 = "+x1+"\n实根2 = "+x2);										
					}														
				}				
			}					
				);
		
		
		
		container.add(jisuan);
		
		
		area = new JTextArea(10,15);
		area.setText("该方程的实根为");
		container.add(area);
		
		setSize(500,400);
		setVisible(true);
				
	}
		
	public static void main(String[] args) {
		
		Chp13_1 application = new Chp13_1();
		application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
	}
	
}