ActionListenerBasics.java

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

public class GUI extends JFrame implements ActionListener {
    JButton numbers [] = new JButton[12];
    JTextField up;
    JPanel num;
    int sum;
    String yo [] = {"1","2"};
    JComboBox Hi = new JComboBox(yo);

    public GUI(){
        num= new JPanel();
        num.setLayout(new GridLayout(4,3));

        //initialize buttons
        numbers[9]= new JButton("+");
        numbers[10]= new JButton("=");
        numbers[11]= new JButton("C");
        for (int i = 0; i < numbers.length; i++) {
            if (i<9)
                numbers[i]=new JButton(i+1+"");
            num.add(numbers[i]);
            numbers[i].addActionListener(this);
        }


        up = new JTextField();
        add(up,BorderLayout.NORTH);
        add(num);
        add(Hi,BorderLayout.SOUTH);

        setVisible(true);
        setSize(200,400);
        setTitle("Kids Calculator");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);

    }

    public void actionPerformed (ActionEvent ae){
        JButton clicked =  (JButton) ae.getSource();

        if (!clicked.getText().equals("=")&& !clicked.getText().equals("C")) {
            up.setText(up.getText() + clicked.getText());//concatenate
            if (!clicked.getText().equals("+")){
                sum+=Integer.parseInt(clicked.getText());
            }
        }
        else if (clicked.getText().equals("C"))
        {
            sum=0;
            up.setText("");
        }
        else
            up.setText(sum+"");





    }
}