How to find a button source in AWT (calculator homework)

I would tend to have each button for the numbers, as well as each button for operands, add text to a text field that is the ‘Input/Output’.

Also have a button = (equals). When the = button is activated, call the ScriptEngine to evaluate the content of the I/O text field and write the result back to it.

E.G.

=

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.EmptyBorder;
import java.util.ArrayList;

// script package introduced in Java 1.6
import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;

class ScriptEngineCalculator implements ActionListener, KeyListener {

    private final JTextField io = new JTextField(15);
    private final ArrayList<JButton> controls = new ArrayList<>();
    private final JPanel ui = new JPanel(new BorderLayout(2, 2));
    private ScriptEngine engine;

    ScriptEngineCalculator() {
        initUI();
    }

    public final void initUI() {
        // obtain a reference to the JS engine
        engine = new ScriptEngineManager().getEngineByExtension("js");

        JPanel text = new JPanel(new GridLayout(0, 1, 3, 3));
        ui.add(text, BorderLayout.PAGE_START);
        Font font = io.getFont();
        font = font.deriveFont(font.getSize() * 1.8f);
        io.setFont(font);
        io.setHorizontalAlignment(SwingConstants.TRAILING);
        io.setFocusable(false);
        text.add(io);

        JPanel buttons = new JPanel(new GridLayout(4, 4, 2, 2));
        ui.add(buttons, BorderLayout.CENTER);
        String[] keyValues = {
            "7", "8", "9", "/",
            "4", "5", "6", "*",
            "1", "2", "3", "-",
            "0", ".", "C", "+"
        };

        for (String keyValue : keyValues) {
            addButton(buttons, keyValue);
        }

        JButton equals = new JButton("=");
        configureButton(equals);
        ui.add(equals, BorderLayout.LINE_END);

        ui.setBorder(new EmptyBorder(5, 5, 5, 5));
    }

    public JComponent getUI() {
        return ui;
    }

    public void addButton(Container c, String text) {
        JButton b = new JButton(text);
        configureButton(b);
        c.add(b);
    }

    public void configureButton(JButton b) {
        Font f = b.getFont();
        b.setFont(f.deriveFont(f.getSize() * 1.5f));
        b.addActionListener(this);
        b.addKeyListener(this);
        controls.add(b);
    }

    public void calculateResult() {
        try {
            Object result = engine.eval(io.getText());
            if (result == null) {
                io.setText("Output was 'null'");
            } else {
                io.setText(result.toString());
            }
        } catch (ScriptException se) {
            io.setText(se.getMessage());
        }
    }

    @Override
    public void actionPerformed(ActionEvent ae) {
        String command = ae.getActionCommand();
        switch (command) {
            case "C":
                io.setText("");
                break;
            case "=":
                calculateResult();
                break;
            default:
                io.setText(io.getText() + command);
                break;
        }
    }

    private JButton getButton(String text) {
        for (JButton button : controls) {
            String s = button.getText();
            if (text.endsWith(s)
                    || (s.equals("=")
                    && (text.equals("Equals") || text.equals("Enter")))) {

                return button;
            }
        }
        return null;
    }

    /* START - Because I hate mice. */
    @Override
    public void keyPressed(KeyEvent ke) { }

    @Override
    public void keyReleased(KeyEvent ke) {
        String s = KeyEvent.getKeyText(ke.getKeyCode());
        JButton b = getButton(s);
        if (b != null) {
            b.requestFocusInWindow();
            b.doClick();
        }
    }

    @Override
    public void keyTyped(KeyEvent ke) { }
    /* END - Because I hate mice. */

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            ScriptEngineCalculator sc = new ScriptEngineCalculator();
            JFrame f = new JFrame("Calculet");
            f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
            f.setContentPane(sc.getUI());
            f.pack();
            f.setMinimumSize(f.getSize());
            f.setLocationByPlatform(true);
            f.setVisible(true);
        });
    }
}