用java编写一个简单计算器

/*

 * @(#)JCalculator.java 1.00 06/17/2015

 */

import java.awt.*;

import java.awt.event.*;

import javax.swing.*;

/**

 * A simple calculator program.

 * 

I saw this program in a QQ group, and help a friend correct it.

 *

 * @author Singyuen Yip

 * @version 1.00 12/29/2009

 * @see JFrame

 * @see ActionListener

 */

public class JCalculator extends JFrame implements ActionListener {

    /**

     * Serial Version UID

     */

    private static final long serialVersionUID = -169068472193786457L;

    /**

     * This class help close the Window.

     * @author Singyuen Yip

     *

     */

    private class WindowCloser extends WindowAdapter {

       public void windowClosing(WindowEvent we) {

           System.exit(0);

       }

    }

    int i;

    // Strings for Digit & Operator buttons.

    private final String[] str = { "7", "8", "9", "/", "4", "5", "6", "*","1",

           "2", "3", "-", ".", "0", "=", "+" };

    // Build buttons.

    JButton[] buttons = new JButton[str.length];

    // For cancel or reset.

    JButton reset = new JButton("CE");

    // Build the text field to show the result.

    JTextField display = new JTextField("0");

    /**

     * Constructor without parameters.

     */

    public JCalculator() {

       super("Calculator");

       // Add a panel.

       JPanel panel1 = new JPanel(new GridLayout(4, 4));

       // panel1.setLayout(new GridLayout(4,4));

       for (i = 0; i < str.length; i++) {

           buttons[i] = new JButton(str[i]);

           panel1.add(buttons[i]);

       }

       JPanel panel2 = new JPanel(new BorderLayout());

       // panel2.setLayout(new BorderLayout());

       panel2.add("Center", display);

       panel2.add("East", reset);

       // JPanel panel3 = new Panel();

       getContentPane().setLayout(new BorderLayout());

       getContentPane().add("North", panel2);

       getContentPane().add("Center", panel1);

       // Add action listener for each digit & operator button.

       for (i = 0; i < str.length; i++)

           buttons[i].addActionListener(this);

       // Add listener for "reset" button.

       reset.addActionListener(this);

       // Add listener for "display" button.

       display.addActionListener(this);

       // The "close" button "X".

       addWindowListener(new WindowCloser());

       // Initialize the window size.

       setSize(800, 800);

       // Show the window.

       // show(); Using show() while JDK version is below 1.5.

       setVisible(true);

       // Fit the certain size.

       pack();

    }  

    public void actionPerformed(ActionEvent e) {

       Object target = e.getSource();

       String label = e.getActionCommand();

       if (target == reset)

           handleReset();

       else if ("0123456789.".indexOf(label) > 0)

           handleNumber(label);

       else

           handleOperator(label);

    }

    // Is the first digit pressed?

    boolean isFirstDigit = true;

    /**

     * Number handling.

     * @param key the key of the button.

     */

    public void handleNumber(String key) {

       if (isFirstDigit)

           display.setText(key);

       else if ((key.equals(".")) && (display.getText().indexOf(".") < 0))

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

       else if (!key.equals("."))

           display.setText(display.getText() + key);

       isFirstDigit = false;

    }

    /**

     * Reset the calculator.

     */

    public void handleReset() {

       display.setText("0");

       isFirstDigit = true;

       operator = "=";

    }

    double number = 0.0;

    String operator = "=";

    /**

     * Handling the operation.

     * @param key pressed operator's key.

     */

    public void handleOperator(String key) {

       if (operator.equals("+"))

           number += Double.valueOf(display.getText());

       else if (operator.equals("-"))

           number -= Double.valueOf(display.getText());

       else if (operator.equals("*"))

           number *= Double.valueOf(display.getText());

       else if (operator.equals("/"))

           number /= Double.valueOf(display.getText());

       else if (operator.equals("="))

           number = Double.valueOf(display.getText());

       display.setText(String.valueOf(number));

       operator = key;

       isFirstDigit = true;

    }

    public static void main(String[] args) {

       new JCalculator();

    }

}

运行界面：

package swing;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
@SuppressWarnings("serial")
public class Calculator extends JFrame{
	JTextField jt1 ,jt2 ,jt3;
	JLabel jLabel;
	JButton equButton,addButton,reduceButton,mulButton,divButton;
	public Calculator() {
		super("简易计算器");
		JPanel contentPanel = new JPanel();
		contentPanel.setLayout(new GridLayout(2, 0));
		JPanel uJPanel = new JPanel();
		Dimension preferredSize = new Dimension(50, 29);
		GridBagConstraints gbc = new GridBagConstraints();
		uJPanel.setLayout(new GridBagLayout());
		gbc.gridx = GridBagConstraints.RELATIVE;
		gbc.gridy = 0;
		gbc.fill = GridBagConstraints.HORIZONTAL;
		gbc.insets = new Insets(1, 2, 1, 2);
		jt1 = new JTextField(4);
		jLabel = new JLabel();
		jLabel.setPreferredSize(new Dimension(10, 29));
		jt2 = new JTextField(4);
		equButton = new JButton("=");
		ActionListener myActionListener = new MyActionListener();
		equButton.addActionListener(myActionListener);
		jt3 = new JTextField(8);
		jt1.setPreferredSize(preferredSize);
		jt2.setPreferredSize(preferredSize);
		jt3.setPreferredSize(preferredSize);
		uJPanel.add(jt1,gbc);
		uJPanel.add(jLabel,gbc);
		uJPanel.add(jt2,gbc);
		uJPanel.add(equButton,gbc);
		gbc.weightx = 1;
		uJPanel.add(jt3,gbc);
		contentPanel.add(uJPanel);
		JPanel dJPanel = new JPanel();
		dJPanel.setLayout(new FlowLayout(FlowLayout.CENTER, 8, 2));
		addButton = new JButton("+");
		reduceButton = new JButton("-");
		mulButton = new JButton("*");
		divButton = new JButton("/");
		addButton.addActionListener(myActionListener);
		reduceButton.addActionListener(myActionListener);
		mulButton.addActionListener(myActionListener);
		divButton.addActionListener(myActionListener);
		dJPanel.add(addButton);
		dJPanel.add(reduceButton);
		dJPanel.add(mulButton);
		dJPanel.add(divButton);
		contentPanel.add(dJPanel);
		this.setContentPane(contentPanel);
		this.pack();
		this.setLocationRelativeTo(null);
		this.setDefaultCloseOperation(3);
		this.setVisible(true);
	}
	class MyActionListener implements ActionListener{
		Double d1,d2,d3;
		String operator = "";
		public void actionPerformed(ActionEvent e) {
			String fun = e.getActionCommand();
			if (!fun.equals("=")) {
				jLabel.setText(fun);
				operator = fun;
			}else {
				d1 = jt1.getText().equals("")?null:Double.valueOf(jt1.getText());
				d2 = jt2.getText().equals("")?null:Double.valueOf(jt2.getText());
				d3 = calculate(d1,d2,operator);
				jt3.setText(d3==null ? "":d3.toString());
				jt3.setCaretPosition(0);
			}
		}
	}
	Double calculate(Double d1,Double d2,String operator){
		if (d1 == null || d2 == null) {
			return null;
		}
		Double d3 = null;
		switch (operator) {
		case "+":
			d3 = d1 + d2;
			break;
		case "-":
			d3 = d1 - d2;
			break;
		case "*":
			d3 = d1 * d2;
			break;
		case "/":
			d3 = d1 / d2;
			break;
		}
		return d3;
	}
	public static void main(String[] args) {
		new Calculator();
	}
}

我已经写好了。需要的话，撩我

不错，都有现成的了
~~

你这是样本吗？不是已经写好了？