谁来帮我看看 改正哈 谢谢了? 400 报错

谁来帮我看看 改正哈 谢谢了? 400 报错

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
public class Quad_Gui_1 extends JFrame implements ActionListener{
private JTextField a=new JTextField(10);
private JTextField b=new JTextField(10);
private JTextField c=new JTextField(10);
private JLabel r=new JLabel("一元二次方程求根");
private JLabel A=new JLabel("A:");
private JLabel B=new JLabel("B:");
private JLabel C=new JLabel("C:");
private JLabel x1=new JLabel();
private JLabel x2=new JLabel();
private JLabel X1=new JLabel("X1:");
private JLabel X2=new JLabel("X2:");
private JLabel js=new JLabel("计算");
public Quad_Gui_1()
{
	super("Quad");
	JPanel contentPane=(JPanel)getContentPane();
	contentPane.setLayout(new BorderLayout());
	JPanel p1=new JPanel();
	JPanel p2=new JPanel(new GridLayout(0,2));
	JPanel p3=new JPanel();
	contentPane.setBorder(new EmptyBorder(10,10,10,10));
	p1.add(r,BorderLayout.CENTER);
	p2.add(A);
	p2.add(a);
	p2.add(B);
	p2.add(b);
	p2.add(C);
	p2.add(c);
	p2.add(X1);
	p2.add(x1);
	p2.add(X2);
	p2.add(x2);
	p3.add(js,BorderLayout.NORTH);
	js.addActionListener(this);
	contentPane.add(p1,BorderLayout.NORTH);
	contentPane.add(p2,BorderLayout.CENTER);
	contentPane.add(p3,BorderLayout.SOUTH);
	pack();
	setVisible(true);
}
public void actionPerformed(ActionEvent event)
{
	String command=event.getActionCommand();
	if(command.equals("计算"))
	{double a1=Double.parseDouble(a.getText().trim());
	double b1=Double.parseDouble(b.getText().trim());
	double c1=Double.parseDouble(c.getText().trim());
	cha5.Quad q=new cha5.Quad(a1,b1,c1);
	try{
		q.x1x2();
		x1.setText(Double.toString(q.getX1()));
		x2.setText(Double.toString(q.getX2()));
	}catch(Exception e){
		x1.setText("Error!");
		x2.setText("");
	}
	}

}

	/**
	 * @param args
	 */
	public static void main(String[] args) 
		// TODO Auto-generated method stub
		{		
                          Quad_Gui_1 f=new Quad_Gui_1();
		}
	}

大侠看看吧  就是红颜色标记的地方出错了  我不知道为啥   谁教教我哈