Main.java

package it.lisik.experiments.cleanertest;

import java.lang.ref.Cleaner;

class MyCleaner implements Runnable {
    private int currentInstance;

    public MyCleaner(int currentInstance) {
        this.currentInstance = currentInstance;
    }

    @Override
    public void run() {
//        final String someString = String.valueOf(currentInstance);
        final String someString = "x";
        System.out.println("Instance " + someString + " is about to be destroyed");
    }
}

class SampleClass {
    private static int instancesCount = 0;
    private final int currentInstance;

    SampleClass() {
        currentInstance = instancesCount++;
        System.out.println("Sample Class created, instance number: " + getCurrentInstance());
        Main.CLEANER.register(this, new MyCleaner(getCurrentInstance()));

    }

    public int getCurrentInstance() {
        return currentInstance;
    }
}

public class Main {
    public final static Cleaner CLEANER = Cleaner.create();


    public static void main(String[] args) {
        for (int i = 0; i <= 255; i++) {
            new SampleClass();
        }

        final byte[] bytes = new byte[999999999];

        System.gc();


    }
}