//注意,没有考虑*/和+-的优先级.

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

public class Calculator3 extends JFrame implements ActionListener {

private boolean dotExist, operated, equaled; // 帮助运算的布尔变量

private double storedNumber; // 目前的结果

private char lastOperator; // 表示上一运算符

private JTextField operation; // 结果栏

private JButton dot, plus, minus, multi, div, sqrt, equal, changePN, clear; // 运算符

private JButton[] numbers; // 数字

// 构造者

public Calculator3() {

setTitle("Calculator");

// 初始化变量

dotExist = false; // 表示当前的数是否有小数点

operated = false; // 表示任意运算符是否被按下

equaled = false; // 表示等号是否被按下

storedNumber = 0;

lastOperator = '?';

// 初始化窗口变量

operation = new JTextField("0");

operation.setEditable(false);

numbers = new JButton[10];

for (int i = 0; i < 10; i++)

numbers[i] = new JButton("" + i);

dot = new JButton(".");

plus = new JButton("+");

minus = new JButton("-");

multi = new JButton("*");

div = new JButton("/");

sqrt = new JButton("√");

equal = new JButton("=");

changePN = new JButton("±");

clear = new JButton("AC");

// 将窗口物体放入窗口

GridBagLayout layout = new GridBagLayout();

getContentPane().setLayout(layout);

addComponent(layout, operation, 0, 0, 4, 1);

addComponent(layout, numbers[1], 1, 0, 1, 1);

addComponent(layout, numbers[2], 1, 1, 1, 1);

addComponent(layout, numbers[3], 1, 2, 1, 1);

addComponent(layout, numbers[4], 2, 0, 1, 1);

addComponent(layout, numbers[5], 2, 1, 1, 1);

addComponent(layout, numbers[6], 2, 2, 1, 1);

addComponent(layout, numbers[7], 3, 0, 1, 1);

addComponent(layout, numbers[8], 3, 1, 1, 1);

addComponent(layout, numbers[9], 3, 2, 1, 1);

addComponent(layout, dot, 4, 0, 1, 1);

addComponent(layout, numbers[0], 4, 1, 1, 1);

addComponent(layout, sqrt, 4, 2, 1, 1);

addComponent(layout, plus, 1, 3, 1, 1);

addComponent(layout, minus, 2, 3, 1, 1);

addComponent(layout, multi, 3, 3, 1, 1);

addComponent(layout, div, 4, 3, 1, 1);

addComponent(layout, equal, 5, 0, 2, 1);

addComponent(layout, changePN, 5, 2, 1, 1);

addComponent(layout, clear, 5, 3, 1, 1);

}

// 对按钮进行反应的方法

public void actionPerformed(ActionEvent e) {

JButton btn = (JButton) e.getSource();

if (btn == clear) {

operation.setText("0");

dotExist = false;

storedNumber = 0;

lastOperator = '?';

} else if (btn == equal) {

operate('=');

equaled = true;

} else if (btn == plus) {

operate('+');

equaled = false;

} else if (btn == minus) {

operate('-');

equaled = false;

} else if (btn == multi) {

operate('*');

equaled = false;

} else if (btn == div) {

operate('/');

equaled = false;

} else if (btn == changePN) {

operate('p');

operate('=');

equaled = true;

} else if (btn == sqrt) {

operate('s');

operate('=');

equaled = true;

} else {

if (equaled)

storedNumber = 0;

for (int i = 0; i < 10; i++)

if (btn == numbers[i]) {

if (operation.getText().equals("0"))

operation.setText("" + i);

else if (!operated)

operation.setText(operation.getText() + i);

else {

operation.setText("" + i);

operated = false;

}

}

if (btn == dot && !dotExist) {

operation.setText(operation.getText() + ".");

dotExist = true;

}

}

}

// 进行运算的方法

private void operate(char operator) {

double currentNumber = Double.valueOf(operation.getText())

.doubleValue();

if (lastOperator == '?')

storedNumber = currentNumber;

else if (lastOperator == '+')

storedNumber += currentNumber;

else if (lastOperator == '-')

storedNumber -= currentNumber;

else if (lastOperator == '*')

storedNumber *= currentNumber;

else if (lastOperator == '/')

storedNumber /= currentNumber;

else if (lastOperator == 'p')

storedNumber *= -1;

else if (lastOperator == 's')

storedNumber = Math.sqrt(currentNumber);

else if (lastOperator == '=' && equaled)

storedNumber = currentNumber;

operation.setText("" + storedNumber);

operated = true;

lastOperator = operator;

}

// 快捷使用GridBagLayout的方法

private void addComponent(GridBagLayout layout, Component component,

int row, int col, int width, int height) {

GridBagConstraints constraints = new GridBagConstraints();

constraints.fill = GridBagConstraints.BOTH;

constraints.insets = new Insets(10, 2, 10, 2);

constraints.weightx = 100;

constraints.weighty = 100;

constraints.gridx = col;

constraints.gridy = row;

constraints.gridwidth = width;

constraints.gridheight = height;

layout.setConstraints(component, constraints);

if (component instanceof JButton)

((JButton) component).addActionListener(this);

getContentPane().add(component);

}

// 主方法初始化并显示窗口

public static void main(String[] args) {

Calculator3 calc = new Calculator3();

calc.setSize(290, 400);

calc.setVisible(true);

}

}