Java 乘法小程序

当试图创建一个java小程序来帮助小学生学习乘法时。使用Math.random方法或随机对象生成两个正的一位数整数。运行小程序时出现问题。我对java编程相当陌生，这可能是一个非常简单的修复方法

请参阅下面我的当前代码

import java.awt.*;
import java.awt.Graphics;
import java.lang.Object;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;



public class NewJApplets extends JApplet implements ActionListener
{
public Graphics brush;

Random rand = new Random();
int number1 = rand.nextInt(10);
int number2 = rand.nextInt(10);
JLabel question = new JLabel("What is " + number1 + " times " + number2 + "?");
JLabel Result = new JLabel("");
JTextField answer = new JTextField(3);
JButton checkAnswer = new JButton("Check Answer");
Font font1 = new Font("Teen", Font.BOLD, 30);
Font font2 = new Font("Teen", Font.ITALIC, 36);
String right = "Very good!!!";
String wrong = "No. Please try again.";
Container con = getContentPane();

public void init()
{
setLayout(new FlowLayout());
con.setBackground(Color.YELLOW);
question.setLocation(20, 20);
question.setFont(font1);
Result.setLocation (0,100);
Result.setFont(font1);
con.add(question);
con.add(Result);
answer.setLocation(20, 40);

con.add(answer);
checkAnswer.setLocation(20, 60);
con.add(checkAnswer);

checkAnswer.addActionListener(new ActionListener()
{

public void paint()
{
brush.setFont(font2);
}

public void actionPerformed(ActionEvent e)
{

int ans = Integer.parseInt(answer.getText());

if(ans == number1 * number2)
{
answer.setText("");

Random rand = new Random();


int number1 = rand.nextInt(9) + 1;
int number2 = rand.nextInt(9) + 1;
brush.drawString(right, 20, 80);
Result.setText(right);
repaint();
validate();

}

else
{
answer.setText("");
Result.setText(wrong);
brush.drawString(wrong, 80, 20);
repaint();
validate();
}
}
}
);
}

@Override
public void actionPerformed(ActionEvent e)
{
answer.setText("");
Random rand = new Random();
int number1 = rand.nextInt(10);
int number2 = rand.nextInt(10);
}
}

小程序编译时没有任何问题，但是在尝试运行小程序时，我收到以下错误消息

“类似乎不是小程序。”带有继续或取消选项。在快速按下continue之后，我收到了该应用程序，它似乎正在工作。但是，我没有给出正确的结果，而是在jGRASP中看到如下输出：

Exception in thread "AWT-EventQueue-1" java.lang.NullPointerException
at NewJApplets$1.actionPerformed(NewJApplets.java:65)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6505)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
    at java.awt.Component.processEvent(Component.java:6270)
    at java.awt.Container.processEvent(Container.java:2229)
    at java.awt.Component.dispatchEventImpl(Component.java:4861)
    at java.awt.Container.dispatchEventImpl(Container.java:2287)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
    at java.awt.Container.dispatchEventImpl(Container.java:2273)
    at java.awt.Component.dispatchEvent(Component.java:4687)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:694)
    at java.awt.EventQueue$3.run(EventQueue.java:692)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
    at java.awt.EventQueue$4.run(EventQueue.java:708)
    at java.awt.EventQueue$4.run(EventQueue.java:706)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

---

在这个问题上有任何帮助都会很好

画笔

对象未初始化，因此您将获得一个

空点异常

您需要在

init（）方法中添加以下行：

brush=this.getGraphics();

java:65-第65行是哪一行？注意：请遵守java命名约定-变量应为小写。1）对代码块使用一致的逻辑缩进。代码的缩进旨在帮助人们理解程序流程。2） 为什么要编写小程序？如果是由于老师的特殊要求，请参考。从链接启动的框架使用起来更容易（对于开发者）和更好的体验（对于用户）。@AndrewThompson请不要在教学小程序上发表意见。如果内容对用户没有帮助，则不值得发布。如果（ans==number1*number2）是第56行。有什么建议吗？@Dgrin91不要发表关于什么是和什么是不合适的意见，谢谢。