GCTest

import java.lang.ref.PhantomReference;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;

public class GCTest {
    @SuppressWarnings("ClassNamingConvention")
    static class A {
        private String myName;

        A(String myName) {
            this.myName = myName;
        }
    }

    public static void main(String[] args) throws InterruptedException {
        //noinspection LocalCanBeFinal
        A a1 = new A("a1");
        //noinspection LocalCanBeFinal
        A a2 = new A("a2");

        final ReferenceQueue<A> collectedReferenced = new ReferenceQueue<>();
        final PhantomReference<A> phantomA1 = new PhantomReference<>(a1, collectedReferenced);
        final PhantomReference<A> phantomA2 = new PhantomReference<>(a2, collectedReferenced);

        System.out.println("a1 -> " + phantomA1);
        System.out.println("a2 -> " + phantomA2);

        a1 = a2;

        //noinspection CallToSystemGC
        System.gc();

        //noinspection InfiniteLoopStatement
        while (true) {
            final Reference<? extends A> elem = collectedReferenced.remove();
            System.out.println("collected: " + elem.toString());
        }
    }
}