This article will guide you to create a simple GUI program using Java Swing to simulate an AND logic gate. The program contains two check boxes and a label. When both check boxes are selected, the label will be displayed in green; otherwise, it will be displayed in red. We will update the display of the tag dynamically by listening to the status change event of the checkbox, and provide a complete code example.

Create an AND door panel

First, create a class called AndGate, which inherits from JPanel and implements the ChangeListener interface. The ChangeListener interface is used to listen for state change events of check boxes.

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

public class AndGate extends JPanel implements ChangeListener {
    private JCheckBox in1;
    private JCheckBox in2;
    private JLabel result;

    public AndGate() {
        super();
        setLayout(new FlowLayout());

        in1 = new JCheckBox("Input 1");
        in1.addChangeListener(this);
        add(in1);

        in2 = new JCheckBox("Input 2");
        in2.addChangeListener(this);
        add(in2);

        result = new JLabel("Red"); // The initial state is Red
        result.setForeground(Color.RED);
        add(result);
    }

    @Override
    public void stateChanged(ChangeEvent e) {
        updateResult();
    }

    private void updateResult() {
        if (in1.isSelected() && in2.isSelected()) {
            result.setText("Green");
            result.setForeground(Color.GREEN);
        } else {
            result.setText("Red");
            result.setForeground(Color.RED);
        }
    }
}

Code explanation:

• The AndGate class inherits from JPanel and can therefore be added as a component to a JFrame.
• in1 and in2 are two JCheckBox objects representing two inputs to the AND gate.
• result is a JLabel object that displays the output results of the AND gate.
• FlowLayout is used to set the layout of the panel so that components are arranged in the order they are added.
• addChangeListener(this) is used to register the current object as a listener for checkbox. When the state of the checkbox changes, the stateChanged method will be called.
• In the stateChanged method, check whether both check boxes are selected. If both are selected, set the text of result to "Green", otherwise set to "Red".

Create the main JFrame

Next, create a main JFrame and add the AndGate panel to it.

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

public class MainFrame extends JFrame {

    public MainFrame() {
        setTitle("AND Gate Example");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());

        AndGate andGate = new AndGate();
        add(andGate, BorderLayout.CENTER);

        pack(); // Automatically adjust the window size to suit the component setLocationRelativeTo(null); // center the window to display setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new MainFrame());
    }
}

Code explanation:

• The MainFrame class inherits from JFrame and is used to create the main window.
• The setTitle method is used to set the title of the window.
• The setDefaultCloseOperation method is used to set the operation when the window is closed. It is set to JFrame.EXIT_ON_CLOSE, which means exiting the program when the window is closed.
• BorderLayout is used to set how the window is laid out, adding the AndGate panel to the center of the window.
• The pack() method is used to automatically resize the window to fit the component.
• The setLocationRelativeTo(null) method is used to center the window to display.
• The setVisible(true) method is used to display the window.
• The SwingUtilities.invokeLater method is used to execute Runnable objects in the event distribution thread to ensure the thread safety of the GUI.

Use images instead of text tags

If you want to use an image instead of a text label, you can load the image using the ImageIcon class and set it to the icon of the JLabel.

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

public class AndGate extends JPanel implements ChangeListener {
    private JCheckBox in1;
    private JCheckBox in2;
    private JLabel result;
    private ImageIcon greenIcon;
    private ImageIcon redIcon;

    public AndGate() {
        super();
        setLayout(new FlowLayout());

        in1 = new JCheckBox("Input 1");
        in1.addChangeListener(this);
        add(in1);

        in2 = new JCheckBox("Input 2");
        in2.addChangeListener(this);
        add(in2);

        // Load the image try {
            greenIcon = new ImageIcon(getClass().getResource("/green.png")); // Replace with your green image path redIcon = new ImageIcon(getClass().getResource("/red.png")); // Replace with your red image path} catch (Exception e) {
            System.err.println("Error loading images: " e.getMessage());
            greenIcon = null;
            redIcon = null;
        }

        result = new JLabel();
        if (redIcon != null) {
            result.setIcon(redIcon); // The initial state is Red
        } else {
            result.setText("Red");
            result.setForeground(Color.RED);
        }
        add(result);
    }

    @Override
    public void stateChanged(ChangeEvent e) {
        updateResult();
    }

    private void updateResult() {
        if (in1.isSelected() && in2.isSelected()) {
            if (greenIcon != null) {
                result.setIcon(greenIcon);
                result.setText("");
            } else {
                 result.setText("Green");
                 result.setForeground(Color.GREEN);
            }

        } else {
            if (redIcon != null) {
                result.setIcon(redIcon);
                 result.setText("");
            } else {
                result.setText("Red");
                result.setForeground(Color.RED);
            }
        }
    }
}

Notes:

• Make sure to place the image files (such as green.png and red.png) in the project's resources directory, or specify the correct image path.
• If the image fails to load, the code falls back to the use text label.

Summarize

Through the above steps, you have successfully created a simple Java Swing program, emulating an AND logic gate. You can extend this program as needed, such as adding more logic gates, or using more complex GUI components. The key is to understand the event listening mechanism and how to use JCheckBox and JLabel components.

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