如何用java编程做一个计算器?

有一个现成的参考一下吧
import java.awt.event.ActionEvent;

public class Application extends JFrame {

protected String str = "";
protected boolean isChar = true;
protected boolean isEqual = false;
protected JTextField textField;

public Application() {
Listener listerner = new Listener(this);
getContentPane().setLayout(null);

JButton button = new JButton("7");
button.addActionListener(listerner);
button.setBounds(12, 69, 43, 27);
getContentPane().add(button);

textField = new JTextField();
textField.setText("0");
textField.setEditable(false);
textField.setHorizontalAlignment(JTextField.RIGHT);
textField.setBounds(12, 22, 377, 27);
getContentPane().add(textField);
textField.setColumns(10);

JButton button_1 = new JButton("8");
button_1.addActionListener(listerner);
button_1.setBounds(103, 69, 43, 27);
getContentPane().add(button_1);

JButton button_2 = new JButton("9");
button_2.addActionListener(listerner);
button_2.setBounds(182, 69, 43, 27);
getContentPane().add(button_2);

JButton button_3 = new JButton("4");
button_3.addActionListener(listerner);
button_3.setBounds(12, 106, 43, 27);
getContentPane().add(button_3);

JButton button_4 = new JButton("5");
button_4.addActionListener(listerner);
button_4.setBounds(103, 106, 43, 27);
getContentPane().add(button_4);

JButton button_5 = new JButton("6");
button_5.addActionListener(listerner);
button_5.setBounds(182, 106, 43, 27);
getContentPane().add(button_5);

JButton button_6 = new JButton("1");
button_6.addActionListener(listerner);
button_6.setBounds(12, 143, 43, 27);
getContentPane().add(button_6);

JButton button_7 = new JButton("2");
button_7.addActionListener(listerner);
button_7.setBounds(103, 143, 43, 27);
getContentPane().add(button_7);

JButton button_8 = new JButton("3");
button_8.addActionListener(listerner);
button_8.setBounds(182, 143, 43, 27);
getContentPane().add(button_8);

JButton button_9 = new JButton("+");
button_9.addActionListener(listerner);
button_9.setBounds(269, 72, 43, 27);
getContentPane().add(button_9);

JButton button_10 = new JButton("-");
button_10.addActionListener(listerner);
button_10.setBounds(346, 72, 43, 27);
getContentPane().add(button_10);

JButton button_11 = new JButton("*");
button_11.addActionListener(listerner);
button_11.setBounds(269, 109, 43, 27);
getContentPane().add(button_11);

JButton button_12 = new JButton("/");
button_12.addActionListener(listerner);
button_12.setBounds(346, 109, 43, 27);
getContentPane().add(button_12);

JButton button_13 = new JButton("=");
button_13.addActionListener(listerner);
button_13.setBounds(346, 143, 43, 27);
getContentPane().add(button_13);

JButton button_14 = new JButton("0");
button_14.addActionListener(listerner);
button_14.setBounds(103, 180, 43, 27);
getContentPane().add(button_14);

JButton btnReset = new JButton("reset");
btnReset.addActionListener(listerner);
btnReset.setBounds(269, 180, 118, 27);
getContentPane().add(btnReset);

JButton button_15 = new JButton(".");
button_15.addActionListener(listerner);
button_15.setBounds(269, 146, 43, 27);
getContentPane().add(button_15);

this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setResizable(false);
this.setSize(442, 260);
this.setLocationRelativeTo(null);
this.setVisible(true);
}

public static void main(String[] args) {
new Application();
}
}

class Listener implements ActionListener {
private Application app = null;

public Listener(Application app) {
this.app = app;
}

public void actionPerformed(ActionEvent e) {
String value = e.getActionCommand();
if (value.matches("[0-9.]")) {
if (app.isChar) {
app.textField.setText("");
app.isChar = false;
}
if (app.isEqual && app.str.matches("[0-9.]*")) {
app.str = "";
app.isEqual = false;
}
app.str += value;
app.textField.setText(app.textField.getText() + value);
} else if (value.matches("[\\+\\-\\*/]")) {
if (!app.str.substring(app.str.length() - 1)
.matches("[\\+\\-\\*/]")) {
app.str += value;
app.isChar = true;
}

} else if ("=".equals(value)) {
app.isEqual = true;
if (app.str.substring(app.str.length() - 1).matches("[\\+\\-]")) {
app.str += "0";
} else if (app.str.substring(app.str.length() - 1)
.matches("[\\*/]")) {
app.str += "1";
}
Interpreter bsh = new Interpreter();
String obj = null;
try {
obj = bsh.eval(app.str).toString();
} catch (Exception exception) {
System.out.println(exception.getMessage());
}

System.out.println(app.str);
app.textField.setText(obj);
app.str = obj;
app.isChar = true;
} else {
app.str = "";
app.textField.setText("0");
}
}
}

我有程序，不知道怎么发给你。
联系的问题

我也正在做

网上能下到的