Java Garbage Collection

public class Main {
	public static void main(String[] args) {
		Object obj = new Object();
		obj = null; // no longer reachable -- eligible for automatic reclamation
		System.gc(); // requests garbage collection (JVM decides when it actually runs)
		System.out.println("Unreachable object may be collected");
	}
}

Login to try C/C++/Java/PHP code in the editor

public class Main {
	public static void main(String[] args) {
		for (int i = 0; i < 1000; i++) {
			Object shortLived = new Object(); // most objects like this die young, in the Young generation
		}
		System.out.println("Short-lived objects collected quickly from the Young generation");
	}
}

Login to try C/C++/Java/PHP code in the editor

public class Main {
	public static void main(String[] args) {
		// Run with: java -XX:+UseG1GC Main
		System.out.println("G1 divides the heap into regions, collecting the most-garbage ones first");
	}
}

Login to try C/C++/Java/PHP code in the editor

public class Main {
	public static void main(String[] args) {
		// Run with: java -XX:+UseZGC Main
		System.out.println("ZGC targets single-digit millisecond pauses on very large heaps");
	}
}

Login to try C/C++/Java/PHP code in the editor

import java.lang.ref.*;
public class Main {
	public static void main(String[] args) {
		Object strong = new Object();
		WeakReference<Object> weak = new WeakReference<>(strong); // reclaimed as soon as no strong refs remain
		SoftReference<Object> soft = new SoftReference<>(strong); // cleared only under memory pressure
		System.out.println(weak.get() != null);
	}
}

Login to try C/C++/Java/PHP code in the editor