F:\java\l1>java Exam1_4 23 432
Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Container.java:621)
at java.awt.Container.add(Container.java:307)
at ApplicationFrame.<init>(Exam1_4.java:27)
at Exam1_4.main(Exam1_4.java:8)
Exception in thread "main" java.lang.NullPointerException
at java.awt.Container.addImpl(Container.java:621)
at java.awt.Container.add(Container.java:307)
at ApplicationFrame.<init>(Exam1_4.java:27)
at Exam1_4.main(Exam1_4.java:8)
import java.awt.*;
import java.awt.event.*;
public class Exam1_4
{
public static void main(String args[])
{
ApplicationFrame AF=new ApplicationFrame();
}
}
class ApplicationFrame extends Frame implements ActionListener
{
Label prompt;
TextField text1,text2;
Button btn;
int a=0,b=0;
public ApplicationFrame()
{
super("我的窗口");
prompt=new Label("请输入两个整型数:");
text1=new TextField(4);
text1=new TextField(4);
btn=new Button("计算");
setLayout(new FlowLayout());
add(prompt);
add(text1);
add(text2);
add(btn);
btn.addActionListener(this);
show();
}
public void actionPerformed(ActionEvent e)
{
a=Integer.parseInt(text1.getText());
b=Integer.parseInt(text2.getText());
}
public void paint(Graphics g)
{
g.drawString("运行结果:"+a+"*"+b+"="+a*b,20,80);
}
}
text1=new TextField(4);
btn=new Button("计算");
好象有点问题,text1和text2吧