Java - Learn Java by Examples

How do I create a JSpinner with a SpinnerListModel?

By Wayan in Swing Last modified: May 24, 2023 0 Comment

This example show you how to create a JSpinner component and pass a SpinnerListModel as the available values of the JSpinner component. The SpinnerListModel can hold a value of collections object and a simple array of object instance.

package org.kodejava.swing;

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

public class JSpinnerCreateDemo extends JFrame {
    public JSpinnerCreateDemo() {
        initializeUI();
    }

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

    private void initializeUI() {
        setSize(500, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());

        // Creating an array of color name that we'll use as the
        // source of our SpinnerListMode.
        String[] colors = new String[]{
                "Red", "Orange", "Yellow", "Green", "Blue", "Purple"
        };
        SpinnerListModel model = new SpinnerListModel(colors);

        // Create a JSpinner instance with a spinner model as the value.
        // This JSpinner will allow us to select a colour name when we
        // press the JButton below.
        final JSpinner spinner = new JSpinner(model);
        getContentPane().add(spinner, BorderLayout.NORTH);

        JButton okButton = new JButton("OK");
        okButton.addActionListener(e -> {
            String color = (String) spinner.getValue();
            System.out.println("Color = " + color);
        });
        getContentPane().add(okButton, BorderLayout.SOUTH);
    }
}

How do I create a JSpinner component?

By Wayan in Swing Last modified: May 24, 2023 0 Comment

JSpinner is a single line input field with two buttons (arrow up and arrow down) that allow us to select a value like number or object from a sequence value. It looks like a combobox without a drop-down.

In the following example we create the default JSpinner that will give us a spinner to select an integer value from it.

package org.kodejava.swing;

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

public class JSpinnerCreate extends JFrame {
    public JSpinnerCreate() {
        initialize();
    }

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

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

        // Create an instance of JSpinner and put it at the top of the frame.
        final JSpinner spinner = new JSpinner();
        getContentPane().add(spinner, BorderLayout.NORTH);

        // Create a JButton and print out the value of the JSpinner when
        // the button is clicked.
        JButton okButton = new JButton("OK");
        okButton.addActionListener(e -> {
            Integer value = (Integer) spinner.getValue();
            System.out.println("value = " + value);
        });
        getContentPane().add(okButton, BorderLayout.SOUTH);
    }
}

How do I generate UUID / GUID in Java?

By Wayan in Core API, Util Package Last modified: May 24, 2023 0 Comment

UUID / GUID (Universally / Globally Unique Identifier) is frequently use in programming. Some of its usage are for creating random file names, session id in web application, transaction id and for record’s primary keys in database replacing the sequence or auto generated number.

To generate UUID in Java we can use the java.util.UUID class. This class was introduced in JDK 1.5. The UUID.randomUUID() method return a UUID object. To obtain the value of the random string generated we need to call the UUID.toString() method.

We can also get the version and the variant of the UUID using the version() method and variant() method respectively. Let’s see the code snippet below:

package org.kodejava.util;

import java.util.UUID;

public class RandomStringUUID {
    public static void main(String[] args) {
        // Creating a random UUID (Universally unique identifier).
        UUID uuid = UUID.randomUUID();
        String randomUUIDString = uuid.toString();

        System.out.println("Random UUID String = " + randomUUIDString);
        System.out.println("UUID version       = " + uuid.version());
        System.out.println("UUID variant       = " + uuid.variant());
    }
}

The result of our program is:

Random UUID String = 87a20cdd-25da-4dc2-b787-68054ec2c5ca
UUID version       = 4
UUID variant       = 2

How do I write and read object from HTTP Session?

By Wayan in JSP Last modified: May 24, 2023 0 Comment

In this post you will learn how to write and read object from HTTP Session in JavaServer Page. The first example that we are looking at is using the classic JSP scriptlet, this is a very old way to work with JSP, but it is good for you to know a history. We write a JSP scriptlet inside the <% %> symbols. We can use the provided session object. To set an attribute in the session object we use the setAttribute(String name, Object value) method. In the example we create an attribute called loginDate and set the value to the current date.

To read a value from a session object we use the getAttribute(String name) method. This method return a type of Object, so we need to cast it to the original object. In this case we cast it to a java.util.Date. And then we print out the value read from the session object.

<%@ page import="java.util.Date" %>
<%@ page contentType="text/html;charset=UTF-8" %>
<!DOCTYPE html>
<html lang="en">
<head>
    <title>JSP - Session Write</title>
</head>
<body>
<%
// Creates a session attribute named login-date to store a java.util.Date.
session.setAttribute("loginDate", new Date());

// Read back the java.util.Date object from the session attribute.
Date loginDate = (Date) session.getAttribute("loginDate");
%>
Login Date: <%= loginDate %>
</body>
</html>

The second way that you can use to read values from session object is using the JSP Expression Language (EL). It looks like the following code snippet. You can use the sessionScope implicit object combined with the session attribute name. You can see two ways to use the sessionScope object below. The simplest one is to use the attribute name as the EL expression, and it will look smartly to find the value in the available scope.

<!DOCTYPE html>
<%@ page contentType="text/html;charset=UTF-8" %>
<!DOCTYPE html>
<html lang="en">
<head>
    <title>JSP - Session Read EL</title>
</head>
<body>
<p>Login Date: ${sessionScope.loginDate}</p>

<p>Login Date: ${sessionScope["loginDate"]}</p>

<p>Login Date: ${loginDate}</p>
</body>
</html>

How do I get the number of buttons on the mouse?

By Wayan in AWT, Core API Last modified: May 24, 2023 0 Comment

MouseInfo provides methods for getting information about the mouse, such as mouse pointer location and the number of mouse buttons.

package org.kodejava.awt;

import java.awt.*;

public class MouseNumberOfButtons {
    public static void main(String[] args) {
        // Get the number of buttons on the mouse. On systems without a
        // mouse, returns -1. HeadlessException if
        // GraphicsEnvironment.isHeadless() returns true.
        int numberOfButtons = MouseInfo.getNumberOfButtons();
        System.out.println("Mouse Number Of Buttons = " + numberOfButtons);
    }
}

The output of the code snippet above:

Mouse Number Of Buttons = 5