How do I get the methods of a class object?

In this example we show you how to get the methods available in a class object. We show three ways to get the methods, they are:

  • Class.getDeclaredMethods()
  • Class.getMethods()
  • Class.getMethod(String, Class<?>...)
package org.kodejava.lang.reflect;

import java.lang.reflect.Method;

public class GetMethods {
    public static void main(String[] args) {
        GetMethods object = new GetMethods();
        Class<? extends GetMethods> clazz = object.getClass();

        // Get all declared methods including public, protected, private and
        // package (default) access but excluding the inherited methods.
        Method[] methods = clazz.getDeclaredMethods();
        for (Method method : methods) {
            System.out.println("Method name        = " + method.getName());
            System.out.println("Method return type = " + method.getReturnType().getName());

            Class<?>[] paramTypes = method.getParameterTypes();
            for (Class<?> c : paramTypes) {
                System.out.println("Param type         = " + c.getName());
            }

            System.out.println("----------------------------------------");
        }

        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");

        // Get all methods including the inherited method. Using the getMethods()
        // we can only access public methods.
        methods = clazz.getMethods();
        for (Method method : methods) {
            System.out.println("Method name        = " + method.getName());
            System.out.println("Method return type = " + method.getReturnType().getName());

            Class<?>[] paramTypes = method.getParameterTypes();
            for (Class<?> c : paramTypes) {
                System.out.println("Param type         = " + c.getName());
            }

            System.out.println("----------------------------------------");
        }

        try {
            // We can also get method by their name and parameter types, here we
            // are trying to get the add(int, int) method.
            Method method = clazz.getMethod("add", int.class, int.class);
            System.out.println("Method name: " + method.getName());
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
    }

    public int add(int numberA, int numberB) {
        return numberA + numberB;
    }

    protected int multiply(int numberA, int numberB) {
        return numberA * numberB;
    }

    private double div(int numberA, int numberB) {
        return numberA / numberB;
    }
}

How do I associate JLabel component with a JTextField?

In this example we associate a JLabel component with JTextField and JPasswordField using the setLabelFor(). A mnemonic need to be set for the JLabel component and when we press the defined key (ALT + U or ALT + P) a text field will be gained focus.

package org.kodejava.swing;

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

public class JLabelSetForTextField extends JFrame {
    public JLabelSetForTextField() throws HeadlessException {
        initialize();
    }

    private void initialize() {
        setSize(350, 200);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(new FlowLayout(FlowLayout.LEFT));

        JLabel usernameLabel = new JLabel("Username: ");
        JLabel passwordLabel = new JLabel("Password: ");
        JTextField usernameField = new JTextField(20);
        JPasswordField passwordField = new JPasswordField(20);

        // To make the association between the JLabel and JTextField or
        // JPasswordField we need to define the displayed mnemonic and then
        // call JLabel's setLabelFor method.
        usernameLabel.setDisplayedMnemonic(KeyEvent.VK_U);
        usernameLabel.setLabelFor(usernameField);
        passwordLabel.setDisplayedMnemonic(KeyEvent.VK_P);
        passwordLabel.setLabelFor(passwordField);

        getContentPane().add(usernameLabel);
        getContentPane().add(usernameField);
        getContentPane().add(passwordLabel);
        getContentPane().add(passwordField);
    }

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

How do I create JLabel with an image icon?

To create a JLabel with an image icon we can either pass an ImageIcon as a second parameter to the JLabel constructor or use the JLabel.setIcon() method to set the icon.

package org.kodejava.swing;

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

public class JLabelWithIcon extends JFrame {
    public JLabelWithIcon() throws HeadlessException {
        initialize();
    }

    private void initialize() {
        setSize(500, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(new FlowLayout(FlowLayout.LEFT));

        Icon userIcon = new ImageIcon(
                Objects.requireNonNull(this.getClass().getResource("/images/user.png")));
        JLabel userLabel = new JLabel("Full Name :", userIcon, JLabel.LEFT);

        final ImageIcon houseIcon = new ImageIcon(
                Objects.requireNonNull(this.getClass().getResource("/images/house.png")));
        JLabel label2 = new JLabel("Address :", JLabel.LEFT);
        label2.setIcon(houseIcon);

        getContentPane().add(userLabel);
        getContentPane().add(label2);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> new JLabelWithIcon().setVisible(true));
    }
}
JLabel witch Image Icon

JLabel witch Image Icon

How do I create JLabel component?

package org.kodejava.swing;

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

public class JLabelDemo extends JFrame {
    public JLabelDemo() throws HeadlessException {
        initialize();
    }

    private void initialize() {
        setSize(150, 300);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(new FlowLayout());

        // Create some JLabel with Texts and define the horizontal alignment
        JLabel label1 = new JLabel("Username :", JLabel.RIGHT);
        JLabel label2 = new JLabel("Password :", JLabel.RIGHT);
        JLabel label3 = new JLabel("Confirm Password :", JLabel.RIGHT);
        JLabel label4 = new JLabel("Remember Me!", JLabel.LEFT);
        JLabel label5 = new JLabel("Hello, Anybody There?", JLabel.CENTER);

        // Set the vertical alignment for label5 and also set a tool tip for it
        label5.setVerticalAlignment(JLabel.TOP);
        label5.setToolTipText("I have a tool tip with me!");

        getContentPane().add(label1);
        getContentPane().add(label2);
        getContentPane().add(label3);
        getContentPane().add(label4);
        getContentPane().add(label5);
    }

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

How do I create a message dialog box?

This example demonstrate how to create a message dialog box using the JOptionPane class methods. In the code below you’ll see the use of JOptionPane.showMessageDialog(), JOptionPane.showInputDialog() and JOptionPane.showConfirmDialog().

package org.kodejava.swing;

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

public class MessageDialogDemo extends JFrame {
    public MessageDialogDemo() throws HeadlessException {
        initialize();
    }

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

    private void initialize() {
        setSize(500, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        JButton button1 = new JButton("Click Me!");
        button1.addActionListener(e -> {
            // Show a message dialog with a text message
            JOptionPane.showMessageDialog((Component) e.getSource(),
                    "Thank you!");
        });

        JButton button2 = new JButton("What is your name?");
        button2.addActionListener(e -> {
            // Show an input dialog that will ask you to input some texts
            String text = JOptionPane.showInputDialog((Component) e.getSource(),
                    "What is your name?");
            if (text != null && !text.equals("")) {
                JOptionPane.showMessageDialog((Component) e.getSource(),
                        "Hello " + text);
            }
        });

        JButton button3 = new JButton("Close Application");
        button3.addActionListener(e -> {
            // Show a confirmation dialog which will ask to for a YES or NO
            // button.
            int result = JOptionPane.showConfirmDialog((Component) e.getSource(),
                    "Are you sure want to close this application?");
            if (result == JOptionPane.YES_OPTION) {
                System.exit(0);
            } else if (result == JOptionPane.NO_OPTION) {
                // Do nothing, continue to run the application
            }
        });

        setLayout(new FlowLayout(FlowLayout.CENTER));
        getContentPane().add(button1);
        getContentPane().add(button2);
        getContentPane().add(button3);
    }
}
Message Dialog Box with JOptionPane

Message Dialog Box with JOptionPane