新手java GUI
package practice;
import java.awt.*;
import java.awt.event.*;
public class TFMath {
public static void main(String args []){
new TTFrame().launchFrame();
}
}
class TTFrame extends Frame{
TextField num1,num2,num3;
public void launchFrame(){
TextField num1=new TextField(10);
TextField num2=new TextField(10);
TextField num3=new TextField(15);
setLayout(new FlowLayout());
Button b1=new Button("=");
Label l=new Label("+");
b1.addActionListener(new MyMonitor());
add(num1);
add(l);
add(num2);
add(b1);
add(num3);
pack();
setVisible(true);
}
class MyMonitor implements ActionListener{
public void actionPerformed(ActionEvent e) {
int n1=Integer.parseInt(num1.getText());
int n2=Integer.parseInt(num2.getText());
num3.setText("" + (n1+n2));
}
}
}
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at practice.TTFrame$MyMonitor.actionPerformed(TFMath.java:34)
at java.awt.Button.processActionEvent(Button.java:409)
at java.awt.Button.processEvent(Button.java:377)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
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myeclipse上运行 输入1,2 点击“=”出错误。求指点,谢谢。
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这里声明错误,应该是