简易计算器

package org.tarena.day01;

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

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

public class CalculatorDemo implements ActionListener {

    static boolean append = true;

    JTextField jt = new JTextField(21);

    //简单计算器
    public void makeCalculator() {
        JFrame jf = new JFrame("CalculatorDemo");
        JPanel one = new JPanel();
        JPanel two = new JPanel();
        String[] str = { "BackS", "CE", "cir", "+/-", "7", "8", "9", "/", "4",
                "5", "6", "*", "1", "2", "3", "-", "0", ".", "=", "+" };
        // 添加一个JPanel 和一个JLabel
        one.setLayout(new FlowLayout());

        one.add(jt);

        two.setLayout(new GridLayout(5, 4));
        for (int i = 0; i < 20; i++) {
            JButton jbut = new JButton(str[i]);
            jbut.addActionListener(this);
            two.add(jbut);
        }

        jf.add(one, BorderLayout.NORTH);
        jf.add(two, BorderLayout.CENTER);

        jt.setEditable(false);
        jf.setSize(250, 200);
        jf.setLocation(450, 500);
        jf.setVisible(true);
        jf.setResizable(false);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    String num1 = "0";

    String operator = "+";

    public void actionPerformed(ActionEvent e) {
        String comm = e.getActionCommand();
        if ("0123456789".indexOf(comm) != -1) {//也可以用正则验证
            if (append) {// 追加
                String s = jt.getText();
                jt.setText(s + comm);
            } else {// 替换
                jt.setText(comm);
                append = true;
            }
        } else if ("+-*/".indexOf(comm) != -1) {
            num1 = jt.getText();
            operator = comm;
            append = false;
        } else if ("=".equals(comm)) {
            String num2 = jt.getText();
            double d1 = Double.parseDouble(num1);
            double d2 = Double.parseDouble(num2);
            if ("+".equals(operator)) {
                d1 = d1 + d2;
            } else if ("-".equals(operator)) {
                d1 = d1 - d2;
            } else if ("*".equals(operator)) {
                d1 = d1 * d2;
            } else if ("/".equals(operator)) {
                d1 = d1 / d2;
            }
            jt.setText(d1 + "");
            append = false;
        } else if (".".equals(comm)) {//追加小数点；
            String temp = jt.getText();
            jt.setText(temp + ".");
            append = true;
        } else if ("+/-".equals(comm)) {
            String temp = jt.getText();
            if (temp.startsWith("-")) {
                jt.setText(temp.substring(1));
            } else {
                jt.setText("-" + temp);
            }
        } else if ("CE".equals(comm) || "C".equals(comm)) {
            jt.setText("0");
            append = false;
        } else if ("BackS".equals(comm)) {
            String temp = jt.getText();
            if (temp.length() > 0) {
                jt.setText(temp.substring(0, temp.length() - 1));
            }
        }
    }

    public static void main(String[] args) {
        CalculatorDemo c = new CalculatorDemo();
        c.makeCalculator();
    }

}