随机产生的＋－×/运算，我要在界面上添加一个back的按钮，返回上一个题目，怎么写啊，各位帮帮忙。
package com.gui1;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Calculator implements ActionListener
{
private JFrame frame;
private Container contentPane;
private JButton OKBtn;
private JButton nextBtn;
private JButton ExitBtn;
private JButton outBtn;
private JButton backBtn;
private JLabel num1Lbl;//
private JLabel operLbl;
private JLabel num2Lbl;//
private JTextField answerText;//
private JLabel lblA,lblACount;
private JLabel lblB,lblBCount;
private JLabel lblC,lblCCount;
private JLabel informLbl;
private int countA;//
private int countB;//
private int countC;//
private String oper[]={"+","-","*","/"};
private int n1,n2,n3;
private int operNum;
private Timer timer;
private JLabel lblT1,lblT2;
public Calculator()
{
frame=new JFrame("Pupil Exam System");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setBounds(400,200,500,300);
contentPane=frame.getContentPane();
initGUI();
}
public void initGUI()
{
contentPane.setLayout(new CardLayout());
contentPane.add(getPanel(0),"");
//--------------------------------------
}
public void actionPerformed(ActionEvent e)
{
if(e.getSource()==outBtn)
{
OKBtn.setEnabled(true);
nextBtn.setEnabled(true);
backBtn.setEnabled(true);
lblACount.setText(0+"");
lblBCount.setText(0+"");
lblCCount.setText(0+"");
outBtn.setEnabled(false);
answerText.setEnabled(true);
lblT1.setText("29");
lblT2.setText("60");
timer.start();
question();
}
if(e.getSource()==OKBtn||e.getSource()==answerText)
{
if(answerText.getText().trim().length()==0)
{
answerText.grabFocus();
return;
}
int n;
try
{
n=Integer.parseInt(answerText.getText().trim());
}catch(Exception e1)
{
informLbl.setText("Please input right answer");
answerText.setText("");
answerText.grabFocus();
return;
}
if(n==getN3())
{
int value=Integer.parseInt(lblACount.getText().trim());
lblACount.setText(value+1+"");
}
else
{
int value=Integer.parseInt(lblBCount.getText().trim());
lblBCount.setText(value+1+"");
}
question();
answerText.setText("");
answerText.grabFocus();
}
if(e.getSource()==nextBtn)
{
int value=Integer.parseInt(lblCCount.getText().trim());
lblCCount.setText(value+1+"");
question();
answerText.grabFocus();
}
if(e.getSource()==ExitBtn)
{
(new Exit()).go();
}
if(e.getSource()==backBtn)
{
}
if(e.getSource()==timer)
{
int value=Integer.parseInt(lblT2.getText().trim());//秒数
int value1=Integer.parseInt(lblT1.getText().trim());//分钟
value--;
if(value>=10)
lblT2.setText(value+"");
else
lblT2.setText("0"+value);
if(value==0)
{
lblT2.setText(60+"");
value1--;
if(value1>=10)
lblT1.setText(value1+"");
else
lblT1.setText("0"+value1);
/*
if(value1==0)
{
timer.stop();
OKBtn.setEnabled(false);
nextBtn.setEnabled(false);
outBtn.setEnabled(false);
answerText.setEnabled(false);
informLbl.setText("");
}*/
}
}
int a=Integer.parseInt(lblACount.getText().trim());
int b=Integer.parseInt(lblBCount.getText().trim());
int c=Integer.parseInt(lblCCount.getText().trim());
if(a+b+c==25)
{
OKBtn.setEnabled(false);
nextBtn.setEnabled(false);
outBtn.setEnabled(false);
answerText.setEnabled(false);
informLbl.setText("test over");
timer.stop();
}
}
public int getN3()
{
if(operNum==0)
n3=n1+n2;
if(operNum==1)
n3=n1-n2;
if(operNum==2)
n3=n1*n2;
if(operNum==3)
n3=n1;
return n3;
}
public void question()
{
operNum=(int)(Math.random()*4);
operLbl.setText(oper[operNum]);
n1=(int)(Math.random()*100)+1;
n2=(int)(Math.random()*100)+1;
if(operNum>=0&&operNum<=2)
{
num1Lbl.setText(n1+"");
num2Lbl.setText(n2+"");
}
else
{
num1Lbl.setText(n1*n2+"");
num2Lbl.setText(n2+"");
}
}
public void selectPanel(int id)
{
CardLayout c=(CardLayout)contentPane.getLayout();
contentPane.add(getPanel(id),"");
c.next(contentPane);
}
public JPanel getPanel(int id)
{
JPanel pAll=null;
switch(id)
{
case 0:
{
Panel p11=new Panel(new FlowLayout());
num1Lbl=new JLabel();
operLbl=new JLabel();
num2Lbl=new JLabel();
answerText=new JTextField(5);
p11.add(num1Lbl);
p11.add(operLbl);
p11.add(num2Lbl);
p11.add(new JLabel("="));
p11.add(answerText);
answerText.setEnabled(false);
JPanel p12=new JPanel(new GridLayout(3,1));
JPanel p121=new JPanel(new FlowLayout(FlowLayout.LEFT));
JPanel p122=new JPanel(new FlowLayout(FlowLayout.LEFT));
JPanel p123=new JPanel(new FlowLayout(FlowLayout.LEFT));
lblA=new JLabel("right num: ");
lblB=new JLabel("wrong num: ");
lblC=new JLabel("drop num: ");
lblACount=new JLabel();
lblBCount=new JLabel();
lblCCount=new JLabel();
informLbl=new JLabel("Welcome ,please press start button");
p121.add(lblA);
p121.add(lblACount);
p122.add(lblB);
p122.add(lblBCount);
p123.add(lblC);
p123.add(lblCCount);
p12.add(p121);
p12.add(p122);
p12.add(p123);
JPanel p2=new JPanel(new FlowLayout(FlowLayout.RIGHT));
outBtn=new JButton("start");
OKBtn=new JButton("OK");
nextBtn=new JButton("drop");
ExitBtn=new JButton("exit");
backBtn=new JButton("back");
OKBtn.setEnabled(false);
nextBtn.setEnabled(false);
backBtn.setEnabled(false);
lblT1=new JLabel("00");
lblT2=new JLabel("00");
p2.add(outBtn);
p2.add(OKBtn);
p2.add(nextBtn);
p2.add(backBtn);
p2.add(ExitBtn);
p2.add(lblT1);
p2.add(new JLabel(" : "));
p2.add(lblT2);
JPanel p1=new JPanel(new GridLayout(3,1));
p1.add(informLbl);
p1.add(p11);
p1.add(p12);
pAll=new JPanel(new BorderLayout());
pAll.add(p1,BorderLayout.CENTER);
pAll.add(p2,BorderLayout.SOUTH);
outBtn.addActionListener(this);
OKBtn.addActionListener(this);
nextBtn.addActionListener(this);
ExitBtn.addActionListener(this);
backBtn.addActionListener(this);
answerText.addActionListener(this);
timer=new Timer(1000,this);
}break;
case 1:
{
}break;
}
return pAll;
}
public void go()
{
frame.setVisible(true);
}
public static void main(String args[])
{
(new Calculator()).go();
}
}
