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我一边敲一边现学，不知道哪里错了，也是一样的空白

package homework;

import javax.swing.*;

import java.awt.*;

import java.awt.event.MouseEvent;

import java.awt.event.MouseListener;

public class homework{

public static void main(String[] args) {

cal cal1 = new cal();

}

}

class cal extends JFrame {

MousePolice police ;

JButton jia;

JButton cha;

JButton chu;

JButton ji;

JTextField text1;

JTextField text2;

JTextField answer;

public cal(){

init();

setVisible(true);

setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

}

void init(){

JPanel p = new JPanel();

JFrame window1 = new JFrame("计算");

window1.add(p);

Container con = window1.getContentPane();

con.setBackground(Color.blue);

window1.setBounds(150,150,250,250);

police = new MousePolice();

police.setView(this);

jia = new JButton("加");

cha = new JButton("差");

chu = new JButton("除");

ji = new JButton("积");

text1 = new JTextField(10);

text2 = new JTextField(10);

answer = new JTextField(10);

window1.add(jia);

window1.add(cha);

window1.add(chu);

window1.add(ji);

window1.add(text1);

window1.add(text2);

window1.add(answer);

jia.addMouseListener(police);

cha.addMouseListener(police);

chu.addMouseListener(police);

ji.addMouseListener(police);

addMouseListener(police);

}

}

class MousePolice implements MouseListener {

cal view;

public void setView(cal view) {

this.view = view;

}

public void mousePressed(MouseEvent e) {

double result=1;

String value1 = view.text1.getText();

String value2 = view.text2.getText();

double number1 = Double.parseDouble(value1);

double number2 = Double.parseDouble(value2);

if (e.getSource() == view.jia && e.getButton() == MouseEvent.BUTTON1) {

result = number1 + number2;

} else if (e.getSource() == view.cha && e.getButton() == MouseEvent.BUTTON1) {

result = number1 - number2;

} else if (e.getSource() == view.chu && e.getButton() == MouseEvent.BUTTON1) {

result = number1 / number2;

} else if (e.getSource() == view.ji && e.getButton() == MouseEvent.BUTTON1) {

result = number1 * number2;

}

view.answer.setText(String.valueOf(result));

}

public void mouseReleased(MouseEvent e) {

}

public void mouseEntered(MouseEvent e) {

}

public void mouseExited(MouseEvent e) {

}

public void mouseClicked(MouseEvent e) {

}

}