写的不太好

package Reckoner;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.*;

public class Caculate {

    String[]buttons={"1","2","3","+","←","4","5","6","-","C","7","8","9","*","01",".","0","=","/","02"};
     public Caculate(){

     }
    JPanel buttonPanel1=new JPanel();
    JPanel panelResult=new JPanel();
    JOptionPane jop = new JOptionPane("出错了");
    JLabel expression=new JLabel();
    JLabel result=new JLabel();
    JPanel panel=new JPanel(new GridLayout(2,1));
    String eps = "";
    String res = "";
    int judge=0;
    JMenuBar menuBar=new JMenuBar();
    JMenu menu=new JMenu("菜单");
    JMenuItem menuItem1=new JMenuItem("历史记录");
    JMenuItem menuItem2=new JMenuItem("清空文件");
    JMenuItem menuItem3=new JMenuItem("退出");
    File file=new File("记录.txt");
    JDialog historyDialog=new JDialog();
    JTextArea historyTextArea=new JTextArea();
    FileOutputStream fileOutputStream;



    public void Show()
    {
        JFrame window=new JFrame("AIIT计算器");
        window.setSize(500,400);
        window.setLocationRelativeTo(null);
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        buttonPanel1.setLayout(new GridLayout(4,5));
        window.setLayout(new GridLayout(2,1));
        try {
            file.createNewFile();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        initButton();
        initAll();
        initmenuBar();
        window.setJMenuBar(menuBar);
        window.add(panel);
        window.add(buttonPanel1);
        window.setVisible(true);
    }
    public void initmenuBar()
    {
        menuItem1.addActionListener(new MenuListener());
        menu.add(menuItem1);
        menuItem2.addActionListener(new MenuListener());
        menu.add(menuItem2);
        menuItem3.addActionListener(new MenuListener());
        menu.add(menuItem3);
        menuBar.add(menu);

    }
    public void initButton()
    {
        for(String index:buttons)
        {
            JButton button=new JButton(index);
            button.addActionListener(new ButtonListener());
            buttonPanel1.add(button);
        }
    }
    public void initAll()
    {
        panel.add(expression);
        panel.add(result);
    }
    public void compute()
    {
        double num1=0,num2 = 0;
        num1=Double.parseDouble(eps.split(" ")[0]);
        num2=Double.parseDouble(eps.split(" ")[2]);
        if(eps.split(" ")[1].equals("+"))
        {
            res=String.valueOf(num1+num2);
        }
        else if(eps.split(" ")[1].equals("-"))
        {
            res=String.valueOf(num1-num2);
        }
        else if(eps.split(" ")[1].equals("*"))
        {
            res=String.valueOf(num1*num2);
        }
        else if(eps.split(" ")[1].equals("/"))
        {
            res=String.valueOf(num1/num2);
        }
    }

    public class MenuListener implements ActionListener{

        @Override
        public void actionPerformed(ActionEvent e) {
            String x=e.getActionCommand();
            switch (x)
            {
                case "历史记录":
                    try {
                        FileInputStream fis = new FileInputStream("记录.txt");
                        int length = (int) file.length();
                        byte[] b = new byte[length];
                        fis.read(b);
                        String xx = new String(b);
                        historyTextArea.setText(xx);
                        historyDialog.add(historyTextArea);
                        historyDialog.setSize(300, 400);
                        historyDialog.setLocationRelativeTo(null);
                        historyDialog.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
                        historyTextArea.setEditable(false);
                        historyDialog.setVisible(true);
                        fis.close();
                    }
                    catch (FileNotFoundException ex) {
                        throw new RuntimeException(ex);
                    } catch (IOException ex) {
                        throw new RuntimeException(ex);
                    }
                    break;
                case "清空文件":
                    try {
                        fileOutputStream=new FileOutputStream("记录.txt");
                        eps="";
                        byte[] b =eps.getBytes() ;
                        fileOutputStream.write(b);
                    } catch (FileNotFoundException ex) {
                        throw new RuntimeException(ex);
                    }
                    catch (IOException ex) {
                        throw new RuntimeException(ex);
                    }
                    break;
            }
        }
    }
    public class ButtonListener implements ActionListener
    {

        @Override
        public void actionPerformed(ActionEvent e) {
            String x=e.getActionCommand();
            String i=x;
            switch(x)
            {
                case "1":
                case "2":
                case "3":
                case "4":
                case "5":
                case "6":
                case "7":
                case "8":
                case "9":
                case "0":
                    if(!res.equals(""))
                    {
                        eps="";
                        res="";
                    }
                    if(x.equals(i+""))
                    {
                        eps+=i;

                        expression.setText(eps);
                        break;
                    }
                case "+":
                case "-":
                case "*":
                case "/":
                    char lastChar = eps.charAt(eps.length() - 1);
                    if(lastChar==' ')
                    {
                        jop.showMessageDialog(null, "出错了", "错误", JOptionPane.ERROR_MESSAGE);
                        eps=" ";
                        expression.setText(eps);
                    }
                    else{
                        i = " " + x + " ";
                        eps += i;
                        expression.setText(eps);
                    }
                    break;
                case "←":
                    if (eps.length() > 0) {
                        eps = eps.substring(0, eps.length() - 1);
                        expression.setText(eps);
                    }
                    break;
                case "C":
                    expression.setText("");
                    break;
                case "=":
                    compute();
                    try {
                        fileOutputStream=new FileOutputStream("记录.txt",true);
                        String epss=eps+"="+res+"\n";
                        byte[] b =epss.getBytes();
                        fileOutputStream.write(b);
                    } catch (FileNotFoundException ex) {
                        throw new RuntimeException(ex);
                    } catch (IOException ex) {
                        throw new RuntimeException(ex);
                    }
                    eps="";
                    result.setText(res);
                    break;

            }
        }
    }

    public static void main(String[] args)
    {
        new Caculate().Show();
    }
}