quote:

import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.SwingConstants;
import java.awt.Color;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

public class HesapMakinesi {

/**
* Launch the application.
*/
protected JFrame frame;
protected String islem = "";
protected double ilkSayi, ikinciSayi;
protected boolean islemYapildi = true, noktaKoyuldu = false;
protected JTextField txt_ekran;

public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
HesapMakinesi window = new HesapMakinesi();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}

/**
* Create the application.
*/
public HesapMakinesi() {
initialize();
}

/**
* Initialize the contents of the frame.
*/
private void initialize() {
frame = new JFrame();
frame.setBounds(100, 100, 553, 298);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(null);
frame.addKeyListener(klavyeDinleyici);
frame.setFocusable(true);

JPanel panel = new JPanel();
panel.setBounds(0, 0, 537, 259);
frame.getContentPane().add(panel);
panel.setLayout(null);

txt_ekran = new JTextField();
txt_ekran.setBackground(Color.WHITE);
txt_ekran.setEditable(false);
txt_ekran.setText("0");
txt_ekran.setHorizontalAlignment(SwingConstants.RIGHT);
txt_ekran.setBounds(10, 11, 402, 46);
panel.add(txt_ekran);
txt_ekran.setColumns(10);

JButton btn1 = new JButton("1");
btn1.setBounds(10, 86, 89, 31);
panel.add(btn1);

JButton btn2 = new JButton("2");
btn2.setBounds(109, 86, 89, 31);
panel.add(btn2);

JButton btn3 = new JButton("3");
btn3.setBounds(208, 86, 89, 31);
panel.add(btn3);

JButton btn4 = new JButton("4");
btn4.setBounds(10, 130, 89, 31);
panel.add(btn4);

JButton btn5 = new JButton("5");
btn5.setBounds(109, 128, 89, 31);
panel.add(btn5);

JButton btn6 = new JButton("6");
btn6.setBounds(208, 128, 89, 31);
panel.add(btn6);

JButton btn7 = new JButton("7");
btn7.setBounds(10, 173, 89, 31);
panel.add(btn7);

JButton btn8 = new JButton("8");
btn8.setBounds(109, 170, 89, 31);
panel.add(btn8);

JButton btn9 = new JButton("9");
btn9.setBounds(208, 170, 89, 31);
panel.add(btn9);

JButton btn0 = new JButton("0");
btn0.setBounds(109, 212, 89, 31);
panel.add(btn0);

JButton btn_nokta = new JButton(".");
btn_nokta.setBounds(10, 212, 89, 31);
panel.add(btn_nokta);

JButton btn00 = new JButton("00");
btn00.setBounds(208, 212, 89, 31);
panel.add(btn00);

btn1.addActionListener(dinleyici);
btn2.addActionListener(dinleyici);
btn3.addActionListener(dinleyici);
btn4.addActionListener(dinleyici);
btn5.addActionListener(dinleyici);
btn6.addActionListener(dinleyici);
btn7.addActionListener(dinleyici);
btn8.addActionListener(dinleyici);
btn9.addActionListener(dinleyici);
btn0.addActionListener(dinleyici);
btn00.addActionListener(dinleyici);
btn_nokta.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (!noktaKoyuldu) {
if (!islemYapildi)
txt_ekran.setText(txt_ekran.getText() + ".");
else {
islemYapildi = false;
txt_ekran.setText("0.");
}
noktaKoyuldu = true;
}

}
});

JButton btn_Ce = new JButton("CE");
btn_Ce.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
txt_ekran.setText("");
}
});
btn_Ce.setBounds(422, 11, 99, 46);
panel.add(btn_Ce);

JButton btn_arti = new JButton("+");
btn_arti.setBounds(330, 85, 89, 46);
panel.add(btn_arti);

JButton btn_eksi = new JButton("-");
btn_eksi.setBounds(432, 85, 89, 46);
panel.add(btn_eksi);

JButton btn_carpi = new JButton("X");
btn_carpi.setBounds(330, 142, 89, 46);
panel.add(btn_carpi);

JButton btn_bolu = new JButton("/");
btn_bolu.setBounds(432, 142, 89, 46);
panel.add(btn_bolu);

btn_arti.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
islem = "topla";
try {
ilkSayi = Double.parseDouble(txt_ekran.getText());
} catch (NumberFormatException e1) {
}

txt_ekran.setText("");
}
});

btn_eksi.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
islem = "çıkar";
try {
ilkSayi = Double.parseDouble(txt_ekran.getText());
} catch (NumberFormatException e1) {
}
txt_ekran.setText("");
noktaKoyuldu = false;
}
});

btn_carpi.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
islem = "çarp";
try {
ilkSayi = Double.parseDouble(txt_ekran.getText());
} catch (NumberFormatException e1) {
}
txt_ekran.setText("");
noktaKoyuldu = false;
}
});

btn_bolu.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
islem = "böl";
try {
ilkSayi = Double.parseDouble(txt_ekran.getText());
} catch (NumberFormatException e1) {
}
txt_ekran.setText("");
noktaKoyuldu = false;
}
});

JButton btn_esittir = new JButton("=");
btn_esittir.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {

ikinciSayi = Double.parseDouble(txt_ekran.getText());
switch (islem) {
case "topla":
ekranaYaz(String.valueOf(ilkSayi + ikinciSayi));
break;
case "çıkar":
ekranaYaz(String.valueOf(ilkSayi - ikinciSayi));
break;
case "çarp":
ekranaYaz(String.valueOf(ilkSayi * ikinciSayi));
break;
case "böl":
ekranaYaz(String.valueOf(ilkSayi / ikinciSayi));
break;
default:
break;
}
islemYapildi = true;
islem = "";
noktaKoyuldu = false;
}
});
btn_esittir.setBounds(330, 199, 191, 45);
panel.add(btn_esittir);
}

ActionListener dinleyici = new ActionListener() {
public void actionPerformed(ActionEvent e) {

if (!islemYapildi) {
txt_ekran.setText(txt_ekran.getText() + e.getActionCommand());
} else {
islemYapildi = false;
txt_ekran.setText(e.getActionCommand());
}
}
};

KeyListener klavyeDinleyici = new KeyAdapter() {
public void keyTyped(KeyEvent e) {
if (e.getKeyChar() == '0' || e.getKeyChar() == '1' || e.getKeyChar() == '2' || e.getKeyChar() == '3'
|| e.getKeyChar() == '4' || e.getKeyChar() == '5' || e.getKeyChar() == '6' || e.getKeyChar() == '7'
|| e.getKeyChar() == '8' || e.getKeyChar() == '9') {
if (!islemYapildi) {
txt_ekran.setText(txt_ekran.getText() + e.getKeyChar());
} else {
islemYapildi = false;
txt_ekran.setText("" + e.getKeyChar());
}
}
}
};

public void ekranaYaz(String sayi) {
if (sayi.endsWith(".0"))
txt_ekran.setText(sayi.substring(0, sayi.length() - 2));
else
txt_ekran.setText(sayi);
}
}