java实现简易计算器

用java写的简易版计算器，效果如下图所示：



1、新建一个类，名为Calculator

2、编写如下代码：（注意导包）

import java.awt.BorderLayout;

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;

public class Calculator {
public static void main(String[] args) {
CalculatorFrame frame = new CalculatorFrame();
frame.setSize(300, 300);
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}

}

class CalculatorFrame extends JFrame{
public CalculatorFrame(){
setTitle("小孔简易计算器");
CalculatorPanel panel = new CalculatorPanel();
add(panel);
pack();
}

}

class CalculatorPanel extends JPanel{

private JButton display;
private JPanel panel;
private double result;
private String lastCommand;
private boolean start;

public CalculatorPanel(){
setLayout(new BorderLayout());

result = 0;
lastCommand = "=";
start = true;

display = new JButton("0");
display.setEnabled(false);
add(display,BorderLayout.NORTH);

ActionListener insert = new InsertAction();
ActionListener command = new CommandAction();

panel = new JPanel();
panel.setLayout(new GridLayout(4,4));

addButton("7",insert);
addButton("8",insert);
addButton("9",insert);
addButton("/",command);

addButton("4",insert);
addButton("5",insert);
addButton("6",insert);
addButton("*",command);

addButton("1",insert);
addButton("2",insert);
addButton("3",insert);
addButton("-",command);

addButton("0",insert);
addButton(".",insert);
addButton("=",command);
addButton("+",command);

add(panel,BorderLayout.CENTER);
}

private void addButton(String label,ActionListener listener){
JButton button = new JButton(label);
button.addActionListener(listener);
panel.add(button);
}

private class InsertAction implements ActionListener{
public void actionPerformed(ActionEvent event){
String input = event.getActionCommand();
if(start){
display.setText("");
start = false;
}
display.setText(display.getText() + input);
}
}

private class CommandAction implements ActionListener{
public void actionPerformed(ActionEvent event){

String command = event.getActionCommand();

if(start){
if(command.equals("-")){
display.setText(command);
start = false;
}else
lastCommand = command;
}else{
calculate(Double.parseDouble(display.getText()));
lastCommand = command;
start = true;
}
}
}

public void calculate(double x){
if(lastCommand.equals("+")) result += x;
else if(lastCommand.equals("-")) result -= x;
else if(lastCommand.equals("*")) result *= x;
else if(lastCommand.equals("/")) result /= x;
else if(lastCommand.equals("=")) result = x;
display.setText("" + result);
}

}

3、运行程序，即可体验简易计算器。