Java 实现简易计算器完整代码

最近在学习java的编程，就写了个简易的计算器，可以实现基本的运算，测试目前无bug,下面分享下自己的代码。

首先界面：

整个面板用了BorderLayout布局，分为北，左和中。中部采用网格布局。定义这个类位CalFrame.Java:

package com.example.java;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Arrays;

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

public class CalFrame extends JFrame {

/**
 * 计算器的外观设计
 */
private static final long serialVersionUID = 1L;
private static final int PRE_WIDTH = 500;
private static final int PRE_HEIGHT = 400;

private JTextField text = null;
private JButton button = null;  //存储标记 

private String[] nOp = {"7","8","9","/","sqrt","4","5","6","*","%","1","2","3","-","1/x","0","+/-",".","+","="};
private String[] mOp = {"MC","MR","MS","M+"};
private String[] rOp = {"Back","CE","C"};
private CalService service = new CalService(); 

public CalFrame() {
    this.setTitle("计算器");
    this.setSize(PRE_WIDTH, PRE_HEIGHT);
    this.setLocationRelativeTo(null);
    this.setResizable(false);

    //添加底层
    JPanel panel = new JPanel();
    panel.setLayout(new BorderLayout(10,1));
    panel.add(getTextField(), BorderLayout.NORTH);
    panel.setPreferredSize(new Dimension(PRE_WIDTH, PRE_HEIGHT));

    //west
    JButton[] mButton = getMButton();
    JPanel panel1 = new JPanel();
    panel1.setLayout(new GridLayout(5, 1, 0, 5));
    for (JButton jButton : mButton) {
        panel1.add(jButton);
    }
    panel.add(panel1, BorderLayout.WEST);

    JButton[] rButton = getRButton();
    JPanel panel2 = new JPanel();
    panel2.setLayout(new BorderLayout(1, 5));
    JPanel panel21 = new JPanel();
    panel21.setLayout(new GridLayout(1, 3, 3, 3));
    for (JButton jButton : rButton) {
        panel21.add(jButton);
    }
    panel2.add(panel21,BorderLayout.NORTH);

    JButton[] nButton = getNButton();
    JPanel panel3 = new JPanel();
    panel3.setLayout(new GridLayout(4,5,3,5));
    for (JButton jButton : nButton) {
        panel3.add(jButton);
    }
    panel2.add(panel3, BorderLayout.CENTER);
    panel.add(panel2, BorderLayout.CENTER);

    this.add(panel);
    this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    this.setVisible(true);
}

//返回数字键
private JButton[] getNButton() {
    String[] redButton = {"/","*","-","+","="};
    JButton[] nbutton = new JButton[nOp.length];
    for (int i = 0; i < nOp.length; i++) {
        JButton b = new JButton(this.nOp[i]);
        b.addActionListener(getActionListener());

        Arrays.sort(redButton);
        if (Arrays.binarySearch(redButton, nOp[i]) >= 0) {
            b.setForeground(Color.red);
        }else {
            b.setForeground(Color.blue);
        }
        nbutton[i] = b;
    }
    return nbutton;
}

private JButton[] getRButton() {
    JButton[] rButton = new JButton[rOp.length];
    for (int i = 0; i < rOp.length; i++) {
        JButton b = new JButton(this.rOp[i]);
        b.addActionListener(getActionListener());
        b.setForeground(Color.red);
        rButton[i] = b;
    }
    return rButton;
}

//返回操作健 
private JButton[] getMButton() {
    JButton[] mbutton = new JButton[mOp.length+1];
    mbutton[0] = getButton();
    for (int i = 0; i < this.mOp.length; i++) {
        JButton b = new JButton(this.mOp[i]);
        b.addActionListener(getActionListener());
        b.setForeground(Color.red);
        mbutton[i+1] = b;
    }
    return mbutton;
}

private ActionListener getActionListener() {
    ActionListener actionListener = new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            String cmd = e.getActionCommand();
            String result = null;

            try {
                result = service.callMethod(cmd,text.getText());
            } catch (Exception e2) {
                System.out.println(e2.getMessage());
            }
            if (cmd.indexOf("MC")==0) {
                button.setText("");
            }else if (cmd.indexOf("M")==0) {
                button.setText("M");
            }
            //显示计算结果 
            if (result != null) {
                text.setText(result);
            }
        }
    };
    return actionListener;
}

private JButton getButton() {
    button = new JButton();
    return button;
}

//返回显示框
public JTextField getTextField() {
    text = new JTextField("0",10);
    return text;
}

public static void main(String[] args) {
    new CalFrame();
}
}

接着实现几个基本的操作，加，减，乘，除。考虑到精度和范围的问题.我们定义了一个MyMath类，数据格式使用BigDecimal对象,进行计算。MyMath.java:

package com.example.java;

import java.math.BigDecimal;

public class MyMath {

public static double add(double num1, double num2) {
    BigDecimal first = getBigDecimal(num1);
    BigDecimal second = getBigDecimal(num2);
    return first.add(second).doubleValue();
}

public static double divide(double num1, double num2) {
    BigDecimal first = getBigDecimal(num1);
    BigDecimal second = getBigDecimal(num2);
    return first.divide(second, 3, BigDecimal.ROUND_HALF_UP).doubleValue();
}

public static double multiply(double num1, double num2) {
    BigDecimal first = getBigDecimal(num1);
    BigDecimal second = getBigDecimal(num2);
    return first.multiply(second).doubleValue();
}

public static double subtract(double num1, double num2) {
    BigDecimal first = getBigDecimal(num1);
    BigDecimal second = getBigDecimal(num2);
    return first.subtract(second).doubleValue();
}

/**
 * 为一个double类型创建BigDecimal对象
 * @param number
 * @return
 */
private static BigDecimal getBigDecimal(double number) {
    return new BigDecimal(number);
}

}

最后处理按钮的事件，我们定义了一个CalService类处理业务逻辑:

package com.example.java;

/**
    * 处理业务逻辑
   * @author l
   *
   */
 public class CalService {
  private boolean isSecondNum = false;
 private String lastOp;
 private String firstNum = "0";
 private String secondNum ="null";
 private double store;
 private String numString = "0123456789.";
 private String opString = "+-*/";

 public String callMethod(String cmd, String text) {
if (cmd.equals("C")) {
    return cleanAll();
}else if(cmd.equals("CE")){
    return clear(text);
}else if (cmd.equals("Back")) {
    return backSpace(text);
}else if (numString.indexOf(cmd) != -1) {
    return catNum(cmd,text);
}else if (opString.indexOf(cmd) != -1) {
    return setOp(cmd,text);
}else if (cmd.equals("+/-")) {
    return setNegative(text);
}else if (cmd.equals("1/x")) {
    return setReciprocal(text);
}else if (cmd.equals("sqrt")) {
    return sqrt(text);
}else if (cmd.equals("%")) {
    return cal(text,true);
}else if (cmd.equals("=")) {
    return cal(text,false);
}else{
  return mCmd(cmd,text);
 }
}

 private String cleanAll() {
this.firstNum = "0";
this.secondNum = null;
return this.firstNum;
}

private String clear(String text) {
return "0";
}

private String backSpace(String text) {
return text.equals("0")||text.equals("")? "0" :text.substring(0, text.length()-1);
}

private String catNum(String cmd, String text) {
String result = cmd;
// 如果text不等于0 
if (!"0".equals(text)) {
    if (isSecondNum) {
        isSecondNum = false;
    }else {
        result = text + cmd;
    }
}
if (result.indexOf(".") == 0) {
    result = "0" + result;
}
return result;
}

private String setOp(String cmd, String text) {
this.lastOp = cmd;
this.firstNum = text;
this.secondNum = null;
this.isSecondNum = true;
return null;
}

private String setNegative(String text) {
if (text.indexOf("-") == 0) {
    return text.substring(1, text.length());    
}else{
    return "-"+text;
}
}

//求倒数
private String setReciprocal(String text) {
if (text.equals("0")) {
    return text;
}else{
   this.isSecondNum = true; 
  return String.valueOf(MyMath.divide(1,Double.valueOf(text)));
  }
 }

//求开方
private String sqrt(String text) {
this.isSecondNum = true;
return String.valueOf(Math.sqrt(Double.valueOf(text)));
}

 private String cal(String text, boolean isPercent) {
double secondResult = secondNum == null ? Double.valueOf(text).doubleValue() : Double.valueOf(secondNum).doubleValue();

// 除数为0
if (secondResult == 0 && this.lastOp.equals("/")) {
    return "0";
}
//有%
if (isPercent) {
    secondResult = MyMath.multiply(Double.valueOf(firstNum),MyMath.divide(secondResult,100));
}
if (this.lastOp.equals("+")) {
    firstNum = String.valueOf(MyMath.add(Double.valueOf(firstNum), secondResult));
}else if (this.lastOp.equals("-")) {
    firstNum = String.valueOf(MyMath.subtract(Double.valueOf(firstNum),secondResult));
}else if (this.lastOp.equals("*")) {
    firstNum = String.valueOf(MyMath.multiply(Double.valueOf(firstNum), secondResult));
}else if (this.lastOp.equals("/")) {
    firstNum = String.valueOf(MyMath.divide(Double.valueOf(firstNum), secondResult));
}
secondNum = secondNum == null ? text : secondNum;
this.isSecondNum = true;
return firstNum;
}

//存储
 private String mCmd(String cmd, String text) {
if (cmd.equals("M+")) {
    store = MyMath.add(store, Double.valueOf(text));
}else if (cmd.equals("MC")) {
    store = 0;
}else if (cmd.equals("MR")) {
    isSecondNum = true;
    return String.valueOf(store);
}else if (cmd.equals("MS")) {
    store = Double.valueOf(text).doubleValue();
}
return null;
}  
}

最后的calMethod方法大量使用if else判断不是好的实现方法，感兴趣的可以看看java的设计模式，消除这样的判断。
至此，一个简易的计算器就完成了。欢迎大家给为留言，共同学习。