Java AWT

package example;

import java.awt.*;

public class Calculator extends Frame {

    public Calculator() {
        setTitle("Kalkulator");
        setSize(500, 500);
        setLayout(new BorderLayout());

        dodajUnos();
        dodajBrojeve();
        dodajDugmiceLevo();
        dodajDugmiceDesno();

        setVisible(true);
    }

    private void dodajUnos() {
        Panel borderPanel = new Panel();
        borderPanel.setLayout(new BorderLayout());

        TextField textField = new TextField();
        textField.setSize(new Dimension(300, 300));
        borderPanel.add("North", textField);

        dodajFunkcije(borderPanel);

        add("North", borderPanel);
    }

    private void dodajFunkcije(Panel panel) {
        Panel flowPanel = new Panel();
        flowPanel.setLayout(new FlowLayout());

        flowPanel.add(new Button("SIN"));
        flowPanel.add(new Button("COS"));
        flowPanel.add(new Button("TAN"));
        flowPanel.add(new Button("LOG"));

        panel.add("Center", flowPanel);
    }

    private void dodajDugmiceLevo() {
        Panel leftPanel = new Panel();
        leftPanel.setLayout(new GridLayout(2,1));

        Button button1 = new Button("C");
        Button button2 = new Button("AC");

        leftPanel.add(button1);
        leftPanel.add(button2);

        this.add("West", leftPanel);
    }

    private void dodajDugmiceDesno() {
        Panel rightPanel = new Panel();
        rightPanel.setLayout(new GridLayout(5, 1));

        Button button1 = new Button("+");
        Button button2 = new Button("-");
        Button button3 = new Button("*");
        Button button4 = new Button("/");
        Button button5 = new Button("=");

        button1.setPreferredSize(new Dimension(40, 50));
        button2.setPreferredSize(new Dimension(40, 50));
        button3.setPreferredSize(new Dimension(40, 50));
        button4.setPreferredSize(new Dimension(40, 50));
        button5.setPreferredSize(new Dimension(40, 50));
        button5.setBackground(Color.GREEN);

        rightPanel.add(button1);
        rightPanel.add(button2);
        rightPanel.add(button3);
        rightPanel.add(button4);
        rightPanel.add(button5);

        this.add("East", rightPanel);
    }

    private void dodajBrojeve() {
        Panel gridPanel = new Panel();
        gridPanel.setLayout(new GridLayout(4, 3));

        Button[] buttons = new Button[12];

        for (int i = 0; i < 9; i++) {
            buttons[i] = new Button(Integer.toString(i + 1));
            buttons[i].setSize(50, 50);
        }
        buttons[9] = new Button("^");
        buttons[9].setSize(50, 50);
        buttons[10] = new Button("0");
        buttons[10].setSize(50, 50);
        buttons[11] = new Button(".");
        buttons[11].setSize(50, 50);

        for (Button button : buttons) {
            gridPanel.add(button);
        }

        add("Center", gridPanel);
    }
}