package calframe;  
      
    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 final static int PRE_WIDTH = 500;  
        private final static 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 b : mButton ){  
                panel1.add(b);  
            }  
            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 b : rButton){  
                panel21.add(b);  
            }  
            panel2.add(panel21,BorderLayout.NORTH);  
              
            JButton[] nButton = getNButton();  
            JPanel panel22 = new JPanel();  
            panel22.setLayout(new GridLayout(4,5,3,5));  
            for(JButton b : nButton){  
                panel22.add(b);  
            }  
            panel2.add(panel22,BorderLayout.CENTER);  
            panel.add(panel2,BorderLayout.CENTER);  
              
            this.add(panel);  
            this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);  
            this.setVisible(true);  
      
              
        }  
        //返回显示框  
        private JTextField getTextField(){  
            text = new JTextField("0",10);  
            //text.setSize(480, 50);  
            return text;  
        }  
        //返回数字键  
        private JButton[] getNButton(){  
            String[] redButton = {"/","*","-","+","="};  
            JButton[] nbutton = new JButton[nOp.length];  
            for(int i = 0; i < this.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;  
        }  
        //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 JButton[] getRButton(){  
            JButton[] rbutton = new JButton[rOp.length];  
            for(int i = 0; i < this.rOp.length; i++){  
                JButton b = new JButton(this.rOp[i]);  
                b.addActionListener(getActionListener());  
                b.setForeground(Color.red);  
                rbutton[i] = b;  
            }  
            return rbutton;  
        }  
        private JButton getButton(){  
            button = new JButton();  
            return button;  
        }  
        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;  
        }  
        public static void main(String[] args) {  
            new CalFrame();  
        }  
    }  

    package calframe;  
      
    import java.math.BigDecimal;  
      
    public class MyMath {  
        /** 
         * 为一个double类型创建BigDecimal对象 
         */  
        private static BigDecimal getBigDecimal(double number){  
            return new BigDecimal(number);  
        }  
        public static double add(double num1, double num2) {  
            BigDecimal first = getBigDecimal(num1);  
            BigDecimal second = getBigDecimal(num2);  
            return first.add(second).doubleValue();  
        }  
        public static double subtract(double num1, double num2) {  
            BigDecimal first = getBigDecimal(num1);  
            BigDecimal second = getBigDecimal(num2);  
            return first.subtract(second).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 divide(double num1, double num2) {  
            BigDecimal first = getBigDecimal(num1);  
            BigDecimal second = getBigDecimal(num2);  
            return first.divide(second,3,BigDecimal.ROUND_HALF_UP).doubleValue();  
        }  
    }  


最后处理按钮的事件，我们定义了一个CalService类处理业务逻辑：

[java] view plain copy

    package calframe;  
      
    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 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;  
        }  
      
        public String setOp(String cmd, String text) {  
            this.lastOp = cmd;  
            this.firstNum = text;  
            this.secondNum = null;  
      
            this.isSecondNum = true;  
            return null;  
        }  
      
        public 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;  
        }  
        //求开方  
        public String sqrt(String text){  
            this.isSecondNum = true;  
            return String.valueOf(Math.sqrt(Double.valueOf(text)));  
        }  
        //求倒数  
        public String setReciprocal(String text){  
            if (text.equals("0")){  
                return text;  
            }else{  
                this.isSecondNum = true;  
                return String.valueOf(MyMath.divide(1, Double.valueOf(text)));  
            }  
        }  
        //存储  
        public 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;  
        }  
          
        public String backSpace(String text){  
            return text.equals("0") || text.equals("") ? "0" :text.substring(0,text.length()-1);  
        }  
          
        public String setNegative(String text){  
            if(text.indexOf("-") == 0){  
                return text.substring(1,text.length());  
            }else{  
                return "-" + text;  
            }  
        }  
        public String clearAll(){  
            this.firstNum = "0";  
            this.secondNum = null;  
            return this.firstNum;  
        }  
        public String clear(String text){  
            return "0";  
        }  
          
        public String callMethod(String cmd, String text){  
            if(cmd.equals("C")){  
                return clearAll();  
            }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);  //设置正负号  
            }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);  
            }  
        }  
    }