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。