Java Calculator

Java Calculator

package Calculator;import javax.swing.*;import java.awt.*;import java.awt.event.*;public class CalculatorDome extends JFrame implements ActionListener {    //全局变量    private final String[] components = {"7","8","9","+","4","5","6","-","1","2","3","*",".","0","=","/"};    private boolean flag_firstNumber = true;    String operator = "=";    double digital = 0.0;    String first_number = "";    String second_number = "";    JButton []numbers;    JButton CE;    JTextField message;    //constructor    CalculatorDome(){        super("Calculator");        //initialize        numbers = new JButton[components.length];        CE = new JButton("CE");        message = new JTextField("");        //create container        Container container = this.getContentPane();        JPanel upperpanel = new JPanel();        upperpanel.setLayout(new BorderLayout());        upperpanel.add("Center",message);        upperpanel.add("East",CE);        JPanel lowerpanel = new JPanel();        lowerpanel.setLayout(new GridLayout(4,4));        for(int i = 0;i < components.length; i++)        {            numbers[i] = new JButton(components[i]);            lowerpanel.add(numbers[i]);            numbers[i].addActionListener(this);        }        container.setLayout(new BorderLayout());        container.add("North",upperpanel);        container.add("Center",lowerpanel);        CE.addActionListener(this);        message.addActionListener(this);        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        setSize(800,800);        this.setVisible(true);        this.setBackground(Color.GRAY);    }    public static void main(String[] args){ new CalculatorDome();   }    @Override    public void actionPerformed(ActionEvent e){        Object target = e.getSource();        String label = e.getActionCommand();        if(target == CE){   handleCE();    }        else if("0123456789.".indexOf(label) >= 0){            if(flag_firstNumber)        {   first_number +=label;   }            else if (!flag_firstNumber) {   second_number +=label;  }            handleNumber(label);        }        else{            handleOperator(label);            flag_firstNumber = false;        }    }    public void handleCE(){        message.setText("");        flag_firstNumber = true;        digital = 0.0;        first_number = "";        second_number = "";    }    public void handleNumber(String key){   message.setText(message.getText() + key);  }    public void handleOperator(String key){        message.setText(message.getText() + key);        if(flag_firstNumber) {  operator = key; }        else {    //          System.out.println(first_number);    //          System.out.println(second_number);                double a = Double.parseDouble(first_number);                double b = Double.parseDouble(second_number);                if(operator.equals("+"))        {   digital = a+b;  }                else if(operator.equals("-"))   {   digital = a-b;  }                else if(operator.equals("/"))   {   digital = a/b;  }                else if(operator.equals("*"))   {   digital = a*b;  }                message.setText("" + digital);        }    }}