java 简单的计算器程序

实现实例：

import java.awt.*; import java.awt.event.*; import javax.swing.*; public class Calculator { public static void main(String[] args) { EventQueue.invokeLater(new Runnable() { public void run() { CalculatorFrame frame = new CalculatorFrame(); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setVisible(true); } }); } } /** * A frame with a calculator panel. */ class CalculatorFrame extends JFrame { public CalculatorFrame() { setTitle("Calculator"); 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; // add the display 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); } /** * This action inserts the button action string to the end of the display text. */ 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); } } /** * This action executes the command that the button action string denotes. */ 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; } } } /** * Carries out the pending calculation. * @param x the value to be accumulated with the prior result. */ 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); } }

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