java简单计算器，清除，回退和等号功能

界面已经有了。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.jar.JarFile;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class CalculatorJFrame implements ActionListener
{

private final String[] str = 
{    "7", "8", "9", "/",
     "4", "5", "6", "*",
     "1", "2", "3", "-", 
     ".", "0", "=", "+" 
};

private JFrame frame;
private JButton[ ] buttons;
private JButton reset, back;
private JTextField display;
private JPanel panel1, panel2,panel3,panel4,panel5;
private JLabel label;

/**
 * @param args
 */
public static void main(String[] args) 
{
    // TODO Auto-generated method stub
    CalculatorJFrame that = new CalculatorJFrame();
    that.Layout();

}

public void Layout() 
{
    frame = new JFrame("Calculator");
    Container contentpane = frame.getContentPane();
    frame.setLayout(new BorderLayout());

    label=new JLabel("計算器");
    label.setForeground(Color.BLACK);
    label.setHorizontalAlignment(label.CENTER);

    display = new JTextField("0");
    display.setHorizontalAlignment(JTextField.RIGHT);

    reset=new JButton("C");
    back=new JButton("back");

    panel3 = new JPanel(new GridLayout(4, 4));
    buttons = new JButton[str.length];
    for (int i = 0; i < str.length; i++) 
    {
        buttons[i] = new JButton(str[i]);
        panel3.add(buttons[i]);
        buttons[i].addActionListener(this);
    }

    panel1=new JPanel(new BorderLayout());
    panel1.add("North",label);
    panel1.add("South",display);

    panel2=new JPanel(new GridLayout(1,2));
    panel2.add(reset);
    panel2.add(back);

    panel4=new JPanel(new BorderLayout());
    panel4.add("North",panel2);
    panel4.add("Center",panel3);

    contentpane.add("North",panel1);
    contentpane.add("Center",panel4);

    frame.setSize(200, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);

}

public void actionPerformed(ActionEvent e) 
{
    Object target = e.getSource();
    String label = e.getActionCommand();
    check(label);

}



public void check(String label)
{
    if ("0123456789".indexOf(label) >= 0)
    {
        if(display.getText().equals("0"))
        {
            display.setText(" ");
            show(label);
        }
        else
        {
            show(label);
        }

    }
    else if(".+-*/".indexOf(label) >= 0)
    {
        if(display.getText().indexOf(".") < 0)
        {
            show(label);
        }
    }
}
public void show(String label) 
{
    String s=display.getText();
    if(s.equals("0"))
    {

    }
    display.setText(s+label);

}

}

 public class CalculatorJFrame implements ActionListener {
    private final String[] str = 
    {    "7", "8", "9", "/",
         "4", "5", "6", "*",
         "1", "2", "3", "-", 
         ".", "0", "=", "+" 
    };
    private String optition;
    private JFrame frame;
    private JButton[ ] buttons;
    private JButton reset, back;
    private JTextField display;
    private JPanel panel1, panel2,panel3,panel4,panel5;
    private JLabel label;
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        CalculatorJFrame that = new CalculatorJFrame();
        that.Layout();

    }

    public void Layout() 
    {
        frame = new JFrame("Calculator");
        Container contentpane = frame.getContentPane();
        frame.setLayout(new BorderLayout());

        label=new JLabel("計算器");
        label.setForeground(Color.BLACK);
        label.setHorizontalAlignment(label.CENTER);

        display = new JTextField("0");
        display.setHorizontalAlignment(JTextField.RIGHT);

        reset=new JButton("C");
        back=new JButton("back");

        reset.addActionListener(this);
        back.addActionListener(this);

        panel3 = new JPanel(new GridLayout(4, 4));
        buttons = new JButton[str.length];
        for (int i = 0; i < str.length; i++) 
        {
            buttons[i] = new JButton(str[i]);
            panel3.add(buttons[i]);
            buttons[i].addActionListener(this);
        }

        panel1=new JPanel(new BorderLayout());
        panel1.add("North",label);
        panel1.add("South",display);

        panel2=new JPanel(new GridLayout(1,2));
        panel2.add(reset);
        panel2.add(back);

        panel4=new JPanel(new BorderLayout());
        panel4.add("North",panel2);
        panel4.add("Center",panel3);

        contentpane.add("North",panel1);
        contentpane.add("Center",panel4);

        frame.setSize(200, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);

    }

    public void actionPerformed(ActionEvent e) 
    {
        Object target = e.getSource();
        String label = e.getActionCommand();
        check(label);

    }



    public void check(String label)
    {
        if ("0123456789".indexOf(label) >= 0)
        {
            if(display.getText().equals("0"))
            {
                display.setText(" ");
                show(label);
            }
            else
            {
                show(label);
            }

        }
        else if(".+-*/".indexOf(label) >= 0){
            show(label);
            if(!label.equals("."))
            {
                optition = label;
            }

        }
        else if(label.equals("C")){
            display.setText("0");
        }
        else if(label.equals("back")){
            display.setText(display.getText().substring(0, display.getText().length()-1));
        }
        else if(label.equals("=")){
            int a,b;
            display.setText(display.getText().substring(1, display.getText().length())); 
            String[] str = display.getText().split("\\"+optition);
            a = Integer.parseInt(str[0]); 
            b = Integer.parseInt(str[1]);
            if(optition.equals("+"))
                display.setText(a+b+"");
            else if(optition.equals("-"))
                display.setText(a-b+"");
            else if(optition.equals("*"))
                display.setText(a*b+"");
            else if(optition.equals("/"))
                display.setText(a/b+"");

        }
    }
    public void show(String label) 
    {
        String s=display.getText();
        display.setText(s+label);

    }
}