帮忙看看这个java程序有什么问题

答案：楼主我把你的程序几个比较明显的错误改了一下，至于里面的功能你自己再试下：
  
我修改了一下，你看看能否运行，图片应该是你运行出来的效果吧？
 import java.awt.*;
 import java.awt.event.MouseEvent;
 import java.awt.event.MouseListener;;
  
public class Totalpanel extends java.applet.Applet implements MouseListener {
  public static void main(String[] args) {
   Totalpanel w = new Totalpanel();
  
  w.realp();
  }
  
  TextField text1, text2, text3, text4;
  
 public void realp() {
  
  Frame ff = new Frame("加法计算器");
   GridBagLayout gr = new GridBagLayout();
   GridBagConstraints gc = new GridBagConstraints();
   ff.setLayout(gr);
  
    Label lb;
   Button button1, button2;
   button1 = new Button("=");
   button2 = new Button("clear");
   lb = new Label("+");
   text1 = new TextField(20);
   text2 = new TextField(20);
   text3 = new TextField(20);
   text4 = new TextField(20);
   gc.fill = GridBagConstraints.BOTH;
   gc.weightx = 11;
   gc.weighty = 11;
   gr.setConstraints(text1, gc);
   gc.weightx = 22;
   gr.setConstraints(lb, gc);
   gc.weightx = 33;
   gr.setConstraints(text2, gc);
   gc.weightx = 44;
   gr.setConstraints(button1, gc);
   gc.weightx = 55;
   gc.gridwidth = GridBagConstraints.REMAINDER;
   gr.setConstraints(text3, gc);
   GridBagConstraints gc1 = new GridBagConstraints();
   gc1.fill = GridBagConstraints.BOTH;
   gc1.weightx = 11;
   gc1.weighty = 22;
   gr.setConstraints(text3, gc1);
   gc1.weightx = 22;
   gc1.weighty = 22;
   gc1.gridwidth = GridBagConstraints.REMAINDER;
   gr.setConstraints(button2, gc1);
   ff.addMouseListener(this);
   ff.setSize(500, 300);
   ff.add(text1);
   ff.add(lb);
   ff.add(text2);
   ff.add(button1);
   ff.add(text3);
   ff.add(text4);
   ff.add(button2);
   ff.setVisible(true);
  }
  
 public void mouseClicked(MouseEvent e) {
   String s;
   String r, u;
   s = text1.getText();
   r = text2.getText();
   u = s + r;
   text3.setText(u);
  }
  
 public void mouseMoved(MouseEvent e) {
  }
  
 public void mouseDragged(MouseEvent e) {
  }
  
  
public void mouseEntered(MouseEvent e) {
   // TODO Auto-generated method stub
  
   }
  
 public void mouseExited(MouseEvent e) {
   // TODO Auto-generated method stub
  
   }
  
 public void mousePressed(MouseEvent e) {
   // TODO Auto-generated method stub
  
   }
  
 public void mouseReleased(MouseEvent e) {
   // TODO Auto-generated method stub
  
   }
 }
  
 你不是把触发加法的运算写在mouseClicked事件里了吗？你填完1、2个框后在空白的地方点一下鼠标。。应该是第一个框加上第二个框等于第三个框啊，第四个框你没用到啊。
dad as

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