用java编写一个小计算器(完整的)

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.text.DecimalFormat;

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

public class Calculator {
//计算器面板
private JFrame f = new JFrame("Calculator");
//输入面扳
private JPanel inputPanel = new JPanel();
//加减乘除面板
private JPanel operationPanel = new JPanel();
//数字面板
private JPanel buttonsPanel = new JPanel();

//输入数据文本框
private JTextField input = new JTextField(20);

//退格键
private JButton backspace = new JButton("BackSpace");
//清空
private JButton CE = new JButton("CE ");
//删除
private JButton C = new JButton("C ");

//四则运算符号键
private JButton add = new JButton("+");
private JButton sub = new JButton("-");
private JButton mul = new JButton("*");
private JButton div = new JButton("/");

//小数点
private JButton decimal = new JButton(".");
//等号
private JButton equal = new JButton("=");

//数字键
private JButton zero = new JButton("0");
private JButton one = new JButton("1");
private JButton two = new JButton("2");
private JButton three = new JButton("3");
private JButton four = new JButton("4");
private JButton five = new JButton("5");
private JButton six = new JButton("6");
private JButton seven = new JButton("7");
private JButton eight = new JButton("8");
private JButton nine = new JButton("9");

private String num1 = "";//保存第一个运算数字
private String operator = "";//保存运算符号

public static void main(String[] args) {
new Calculator();//new计算器实例
}

public Calculator(){
//添加组件，布局
inputPanel.add(input);
f.add(inputPanel, BorderLayout.NORTH);

operationPanel.add(backspace);
operationPanel.add(CE);
operationPanel.add(C);
f.add(operationPanel, BorderLayout.CENTER);

buttonsPanel.add(add);
buttonsPanel.add(sub);
buttonsPanel.add(mul);
buttonsPanel.add(div);
buttonsPanel.add(one);
buttonsPanel.add(two);
buttonsPanel.add(three);
buttonsPanel.add(zero);
buttonsPanel.add(four);
buttonsPanel.add(five);
buttonsPanel.add(six);
buttonsPanel.add(decimal);
buttonsPanel.add(seven);
buttonsPanel.add(eight);
buttonsPanel.add(nine);
buttonsPanel.add(equal);
buttonsPanel.setLayout(new GridLayout(4, 4));
f.add(buttonsPanel, BorderLayout.SOUTH);

//注册各个组件监听事件
backspace.addMouseListener(new OperationMouseListener());
CE.addMouseListener(new OperationMouseListener());
C.addMouseListener(new OperationMouseListener());
decimal.addMouseListener(new OperationMouseListener());
equal.addMouseListener(new OperationMouseListener());

//注册四则运算监听
add.addMouseListener(new CalcMouseListener());
sub.addMouseListener(new CalcMouseListener());
mul.addMouseListener(new CalcMouseListener());
div.addMouseListener(new CalcMouseListener());

//注册数字监听事件
zero.addMouseListener(new NumberMouseListener());
one.addMouseListener(new NumberMouseListener());
two.addMouseListener(new NumberMouseListener());
three.addMouseListener(new NumberMouseListener());
four.addMouseListener(new NumberMouseListener());
five.addMouseListener(new NumberMouseListener());
six.addMouseListener(new NumberMouseListener());
seven.addMouseListener(new NumberMouseListener());
eight.addMouseListener(new NumberMouseListener());
nine.addMouseListener(new NumberMouseListener());

f.setVisible(true);
f.pack();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

private class NumberMouseListener implements MouseListener{

public void mouseClicked(MouseEvent e) {
if(input.getText().trim().equals("0")){//如果文本框已经是0，结果还是0
input.setText(((JButton)e.getSource()).getText().trim());
}else{//否则的话，把0添加到后面，譬如文本框是1，结果就为10
input.setText(input.getText().concat(((JButton)e.getSource()).getText().trim()));
}
}

public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}
public void mousePressed(MouseEvent e) {}
public void mouseReleased(MouseEvent e) {}
}

private class CalcMouseListener implements MouseListener{
//如果输入的是运算符号，保存第一个结果和运算符号
public void mouseClicked(MouseEvent e) {
num1 = input.getText().trim();input.setText("");
operator = ((JButton)e.getSource()).getText().trim();
}

public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}
public void mousePressed(MouseEvent e) {}
public void mouseReleased(MouseEvent e) {}
}

private class OperationMouseListener implements MouseListener{

public void mouseClicked(MouseEvent e) {
if(e.getSource() == backspace){//退格键，删除一个直到没有字符删除
String inputText = input.getText();
if(inputText.length() > 0){
input.setText(inputText.substring(0, inputText.length() - 1));
}
}else if(e.getSource() == C){
input.setText("0");//C，清空所有运算数字和符号
num1 = "";
}else if(e.getSource() == CE){
input.setText("0");//CE-->将文本框置为0
}else if(e.getSource() == decimal){
String text = input.getText().trim();
//如果按了小数点，如果文本框已经有小数点，不做任何操作，否则在结果后面加上小数点
if(text.indexOf(".") == -1){
input.setText(text.concat("."));
}
}else if(e.getSource() == equal){
//如果是等号
if(!operator.trim().equals("")){
if(!input.getText().trim().equals("")){
double result = 0D;
if(operator.equals("+")){//执行加法运算
result = Double.parseDouble(num1) + Double.parseDouble(input.getText().trim());
}else if(operator.equals("-")){//减法运算
result = Double.parseDouble(num1) - Double.parseDouble(input.getText().trim());
}else if(operator.equals("*")){//乘法运算
result = Double.parseDouble(num1) * Double.parseDouble(input.getText().trim());
}else if(operator.equals("/")){//除法运算
result = Double.parseDouble(num1) / Double.parseDouble(input.getText().trim());
}

//格式化最终结果，保留两位小数点
input.setText(new DecimalFormat("0.00").format(result));
}
}

}

}

public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}
public void mousePressed(MouseEvent e) {}
public void mouseReleased(MouseEvent e) {}
}

}

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