第二个题目代码:
------------------------------------------------
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class Minicalc{
 public static void main(String[] args){
  JFrame frame=new JFrame("简易计算器");
  Container pane=frame.getContentPane();
  JTextField firstnumber=new JTextField(10);
        JTextField secondnumber=new JTextField(10);
        JTextField result=new JTextField(10);
        JButton addButton=new JButton("+");
        JButton subButton=new JButton("-");
        JButton mulButton=new JButton("*");
        JButton divButton=new JButton("/");
        pane.setLayout(new GridLayout(5,2));
        pane.add(new JLabel("Enter a number"));
        pane.add(firstnumber);
        pane.add(new JLabel("Enter a number"));
        pane.add(secondnumber);     
        pane.add(new JLabel("Result"));
        pane.add(result);
        pane.add(addButton);
        pane.add(subButton);
        pane.add(mulButton);
        pane.add(divButton);        
        DoMath listener=new DoMath(firstnumber,secondnumber,result);
        addButton.addActionListener(listener);
        subButton.addActionListener(listener);
        mulButton.addActionListener(listener);
        divButton.addActionListener(listener);
        frame.pack();
        frame.show();        
        }        
}
class DoMath implements ActionListener{
 private JTextField inputone,inputtwo,output;
    char F[]=(e.getActionCommand())toCharArray();
 DoMath(JTextField first,JTextField second,JTextField result){
  inputone=first;
  inputtwo=second;
  output=result;
 }
 public void actionPerformed(ActionEvent e){
  double first,second;
  first=Double.parseDouble(inputone.getText().trim());
  second=Double.parseDouble(inputtwo.getText().trim());
  switch(F){  
  case '+' : output.setText(String.valueOf(first+second));break;
  case '-' : output.setText(String.valueOf(first-second));break;
  case '*' : output.setText(String.valueOf(first*second));break;
  case '/' : output.setText(String.valueOf(first/second));break; 
  }      
  /*if (e.getActionCommand().equals("+")) 
   output.setText(String.valueOf(first+second));
   else  { if (e.getActionCommand().equals("-")) 
                  output.setText(String.valueOf(first-second));
                  else  {if  (e.getActionCommand().equals("*")) 
                            output.setText(String.valueOf(first*second)) ;
                            else
                             output.setText(String.valueOf(first/second));
                        }
                  }*/
    }
   }