Welcome to NDL4Java!

The Native Dark mode Listener for Java is a wrapper library for the NDL project. It enables Java applications to query whether the user interface of the operating system uses a dark theme.

Usage

Use this library by integrating this library as dependency in your Java based application.

Specify the path to the native NDL library when launching the JVM: -Djava.library.path=<path/to/NDL>

To enable warning-free access to the restricted JVM methods that are required, specify additionally: --enable-native-access=ALL-UNNAMED

Make sure you have installed a Java Development Kit in version 22 or higher to use this library.

Installation

The following sections show how to use NDL4Java as dependency using the build system Gradle.

GitHub Packages

To use NDL4Java as dependency from GitHub Packages, follow the instructions here.

Add the following to your Gradle build script:

repositories {
    maven {
        url = uri('https://maven.pkg.github.com/mhahnfr/ndl4java')
        credentials {
            username = project.findProperty("gpr.user") ?: System.getenv("USERNAME")
            password = project.findProperty("gpr.token") ?: System.getenv("TOKEN")
        }
    }
}

dependencies {
    implementation 'mhahnfr:ndl4java:0.2'
}

Release

The releases of this library can also be used as dependency in your Gradle build script:

repositories {
    ivy {
        url 'https://github.com/'
        patternLayout {
            artifact '/[organisation]/[module]/releases/download/v[revision]/[module]-[revision].jar'
        }
        metadataSources { artifact() }
    }
}

dependencies {
    implementation 'mhahnfr:ndl4java:0.2'
}

Build from source

To build a Java archive file (.jar) that can be included in other projects, simply execute the jar task:

./gradlew jar

Running the above command successfully generates the file build/libs/NDL4Java-<version>.jar.

API

NDL4Java exposes the following classes:

NDL: The wrapped functions from the NDL project.
DarkModeCallback: An interface for registering objects as dark mode listeners.
NDLException: The exception class of this library.

The class NDL exposes the following static methods:

Signature	Description
`boolean queryDarkMode()`	Queries whether the system UI uses a dark theme.
`void registerCallback(DarkModeCallback cb)`	Registers the given callback.
`void deregisterCallback(DarkModeCallback cb)`	Unregisters the given callback.

Since NDL needs access to the native application, it is recommended to not call queryDarkMode() before the java.awt.EventQueue has launched.

Warning

If the method is called before the JVM has initialized the native application, the JVM might crash.

Dark mode callbacks can be registered and unregistered anywhere at any time.

Note

On macOS, make sure to set the Java property apple.awt.application.appearance to system, e.g. System.setProperty("apple.awt.application.appearance", "system"); for incorporating system theme changes into your Java application.

Make sure to set this property before the java.awt.EventQueue has launched for it to have an effect.

Example

// Main.java

import mhahnFr.NDL.NDL;

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

public class Main {
    public static void main(String[] args) {
        System.setProperty("apple.awt.application.appearance", "system"); // Needed on macOS

        NDL.registerCallback(() -> System.out.println("Callback: Dark: " + NDL.queryDarkMode()));

        EventQueue.invokeLater(() -> {
            final var frame = new JFrame("NDL4Java: Example");
            final var label = new JLabel("Dark: " + NDL.queryDarkMode());
            NDL.registerCallback(() -> label.setText("Dark: " + NDL.queryDarkMode()));
            frame.getContentPane().add(label);
            frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
            frame.pack();
            frame.setLocationRelativeTo(null);
            frame.setVisible(true);
        });
    }
}

Compile as follows:

javac -cp <path/to/NDL4Java>/NDL4Java-0.2.jar Main.java

And run as follows:

java -cp .:<path/to/NDL4Java>/NDL4Java-0.2.jar -Djava.library.path=<path/to/NDL> --enable-native-access=ALL-UNNAMED Main

Final notes

This repository is licensed under the terms of the GNU LGPL version 3 or later.

mhahnFr / NDL4Java