Notes

package Calculator;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class Calculator extends JFrame {

private static JButton sum;
private static JButton sub;
private static JButton mul;
private static JButton div;

private static Container c;
private static JTextArea text;
private static JButton[] arrayBtn;
private static JButton equ;
private static double buffer1 ;
private static double buffer2 ;
private static String operation = "";
private static boolean is = false;

public Calculator() {

setSize(500, 500);
c = getContentPane();
c.setLayout(new GridLayout(5, 3, 10, 10));

text = new JTextArea();
text.setText("Result");
text.setFont(new Font("Arial", Font.PLAIN, 20));
text.setEditable(false);
c.add(text);

sum = new JButton("+");
sum.setFont(new Font("Arial", Font.PLAIN, 40));

sum.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {

operation = "+";
is = true;
buffer1=buffer1*100;
}
});
c.add(sum);

sub = new JButton("-");
sub.setFont(new Font("Arial", Font.PLAIN, 40));

sub.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {

operation = "-";
is = true;
buffer1=buffer1*100;

}
});
c.add(sub);

mul = new JButton("*");
mul.setFont(new Font("Arial", Font.PLAIN, 40));
mul.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {

operation = "*";
is = true;
buffer1=buffer1*100;

}
});
c.add(mul);

div = new JButton("/");
div.setFont(new Font("Arial", Font.PLAIN, 40));
div.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {

operation = "/";
is = true;
buffer1=buffer1*100;

}
});
c.add(div);

equ = new JButton("=");
equ.addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent ae) {

buffer2=buffer2*100;


if (operation == "+") {
text.setText(buffer1 + "+" + buffer2 + "=" + (buffer1 + buffer2));
} else if (operation == "-") {
text.setText("" + (buffer1 - buffer2));
}
if (operation == "*") {
text.setText("" + (buffer1 * buffer2));
}
if (operation == "/") {
text.setText("" + (buffer1 / buffer2));
}

buffer1 = 0;
buffer2 = 0;
operation = "";
is = false;

}
});
c.add(equ);
equ.setFont(new Font("Arial", Font.PLAIN, 40));

arrayBtn = new JButton[10];

for (int i = 0; i < arrayBtn.length - 1; i++) {
arrayBtn[i] = new JButton("" + (i + 1));
arrayBtn[i].setFont(new Font("Arial", Font.PLAIN, 40));
arrayBtn[i].addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent ae) {

for (int x = 0; x < arrayBtn.length; x++) {
if (arrayBtn[x] == ae.getSource()) {

/*
if (!is) { buffer1 = Double.parseDouble(""+buffer1+(x + 1));
*/

if (!is) {
String s = String.valueOf(buffer1) + String.valueOf((x + 1));
System.out.println(s);
buffer1 = Double.parseDouble(s);
} else if (is) {

String s2 = String.valueOf(buffer2) + String.valueOf((x + 1));
System.out.println(s2);
buffer2 = Double.parseDouble(s2);

}
}

}

}
});
c.add(arrayBtn[i]);

}

}

public static void main(String[] args) {

Calculator frame = new Calculator();
frame.setVisible(true);
frame.setDefaultCloseOperation(EXIT_ON_CLOSE);

}

}