新手，计算器的问题，请大神指点。

package Study;

import java.awt.Container;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

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

/**
* 简单计算器窗口
*
* @author Sky。 2013-10-18
*/
@SuppressWarnings("serial")
public class ChuangKou extends JFrame implements ActionListener {
    static JTextField field = new JTextField();// 文本框
    static String suanShi;
   
    public static void main(String[] args) {
        new ChuangKou();// 实例化
    }

    /**
     * 窗口属性设置
     */
    public ChuangKou() {
        super("计算器");
        this.setSize(220, 250);// 窗口大小
        Container c=getContentPane();
        JPanel panel = new JPanel();// 面板
        
        panel. setLayout(new GridLayout(0,4, 5, 5));//流布局
        String[] anNiu = { "7", "8", "9", "+", "4", "5", "6", "-", "1", "2", "3",
                "×", ".", "0", "=", "÷","(",")","←","c" };// 按钮名字的组
        // 添加按钮到面板
        for (int i = 0; i < anNiu.length; i++) {
            JButton button = new JButton(anNiu[i]);
            button.addActionListener(this);// 为每个按钮注册监听器
            panel.add(button);
        }

        c.add(panel);// 添加面板到
        c.add(field, "North");// 添加文本框到窗口北部
        setResizable(false);// 固定窗口
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);// 点击关闭窗口结束程序
        this.setVisible(true);// 窗口可见
    }

    /*处理鼠标单击按钮的事件
     * (non-Javadoc)
     * @see java.awt.event.ActionListener#actionPerformed(java.awt.event.ActionEvent)
     */
    @Override
    public void actionPerformed(ActionEvent e) {
        // TODO Auto-generated method stub
        //处理单机数字按钮时的事件
        if (e.getActionCommand().equals("1")) {
            field.setText(field.getText() + "1");
        }
        if (e.getActionCommand().equals("2")) {
            field.setText(field.getText() + "2");
        }
        if (e.getActionCommand().equals("3")) {
            field.setText(field.getText() + "3");
        }
        if (e.getActionCommand().equals("4")) {
            field.setText(field.getText() + "4");
        }
        if (e.getActionCommand().equals("5")) {
            field.setText(field.getText() + "5");
        }
        if (e.getActionCommand().equals("6")) {
            field.setText(field.getText() + "6");
        }
        if (e.getActionCommand().equals("7")) {
            field.setText(field.getText() + "7");
        }
        if (e.getActionCommand().equals("8")) {
            field.setText(field.getText() + "8");
        }
        if (e.getActionCommand().equals("9")) {
            field.setText(field.getText() + "9");
        }
        if (e.getActionCommand().equals(".")) {
            field.setText(field.getText()+".");
        }
        if (e.getActionCommand().equals("0")) {
            field.setText(field.getText() + "0");
        }
        //处理单击加减乘除按钮的事件
        if (e.getActionCommand().equals("+")) {
            field.setText(field.getText()+"+");
        }
        if (e.getActionCommand().equals("-")) {
            field.setText(field.getText()+"-");
        }
        if (e.getActionCommand().equals("×")) {
            field.setText(field.getText()+"×");
        }
        if (e.getActionCommand().equals("÷")) {
            field.setText(field.getText()+"÷");
        }
        if (e.getActionCommand().equals("(")) {
            field.setText(field.getText() + "(");
        }
        if (e.getActionCommand().equals(")")) {
            field.setText(field.getText() + ")");
        }
        //处理单击退格按钮的事件
        if (e.getActionCommand().equals("←")) {
            StringBuffer buffer=new StringBuffer(field.getText());//获取当前文本框的内容
            buffer=buffer.deleteCharAt(buffer.length()-1);//去掉最后一位字符实现退格
            String aString=buffer.toString();    //将StringBuffer转为String型
            field.setText(aString);
        }
        //处理单击等于按钮的事件
        if (e.getActionCommand().equals("=")) {
             suanShi=field.getText();
            
        }
        //处理清除按钮的事件
        if (e.getActionCommand().equals("c")) {
            field.setText("");
        }

    }
}

package Study;

/**
* 计算器算法
*
* @author Sky。 2013-10-19
*/

public class SuanFa {
    static String string = ChuangKou.suanShi;// 文本框中所输入的算式
   
    static void result() {
    }
}