一个java实现的简单计算器

/** @version 1.32 2004-05-05 @author Cay Horstmann */ import java.awt.*; import java.awt.event.*; import javax.swing.*; import java.applet.*; import java.util.*; import java.net.*; import java.io.*; class CalculatorApplet extends JApplet { public void init() { add(new CalculatorPanel()); } } public class Calculator extends CalculatorApplet { public static void main(String[] args) { AppletFrame frame = new AppletFrame(new CalculatorApplet()); frame.setTitle("Calculator"); frame.setSize(200,200); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setVisible(true); } } class AppletFrame extends JFrame implements AppletStub,AppletContext { public AppletFrame(Applet anApplet) { applet=anApplet; add(applet); } public void setVisible(boolean b) { if(b) { applet.init(); super.setVisible(true); applet.start(); } else { applet.stop(); super.setVisible(false); applet.destroy(); } } public boolean isActive() { return true; } public URL getDocumentBase() { return null; } public String getParameter(String name) { return ""; } public URL getCodeBase() { return null; } public AppletContext getAppletContext() { return this; } public void appletResize(int width,int height) { } public AudioClip getAudioClip(URL url) { return null; } public Image getImage(URL url) { return null; } public Applet getApplet(String name) { return null; } public Enumeration getApplets() { return null; } public void showDocument(URL url) { } public void showDocument(URL url,String target) { } public void showStatus(String status) { } public void setStream(String key,InputStream stream) { } public InputStream getStream(String key) { return null; } public Iterator getStreamKeys() { return null; } private Applet applet; } /** A frame with a calculator panel. */ /*class CalculatorFrame extends JFrame { public CalculatorFrame() { setTitle("Calculator"); CalculatorPanel panel = new CalculatorPanel(); add(panel); pack(); } }*/ /** A panel with calculator buttons and a result display. */ class CalculatorPanel extends JPanel { 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(); KeyListener key=new KeyAction(); // add the buttons in a 4 x 4 grid panel = new JPanel(); panel.setLayout(new GridLayout(4, 4)); addButton("7", insert,key); addButton("8", insert,key); addButton("9", insert,key); addButton("/", command,key); addButton("4", insert,key); addButton("5", insert,key); addButton("6", insert,key); addButton("*", command,key); addButton("1", insert,key); addButton("2", insert,key); addButton("3", insert,key); addButton("-", command,key); addButton("0", insert,key); addButton(".", insert,key); addButton("=", command,key); addButton("+", command,key); add(panel, BorderLayout.CENTER); } /** Adds a button to the center panel. @param label the button label @param listener the button listener */ private void addButton(String label, ActionListener listener,KeyListener key) { JButton button = new JButton(label); button.addActionListener(listener); button.addKeyListener(key); 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; } } } private class KeyAction implements KeyListener { public void keyPressed(KeyEvent e) { } public void keyReleased(KeyEvent e) { } public void keyTyped(KeyEvent e) { char c=e.getKeyChar(); int i=c-48; if(i>=0&&i<=9) { String input = c+""; if (start) { display.setText(""); start = false; } display.setText(display.getText() + input); } else if(c=='+'||c=='-'||c=='*'||c=='/'||c=='=') { String command = c+""; 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); } private JButton display; private JPanel panel; private double result; private String lastCommand; private boolean start; }