WeakReference example

ReferencesTest.java

package com.liferay.portal.service;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.Map;

public class ReferencesTest {

	private static ReferenceQueue<Object> referenceQueue = new ReferenceQueue<Object>();

	public static void main(String[] args) {

		new ReferencesTest().doFunction();
	}

	private void doFunction() {

		Map<Integer, String> map = new HashMap<Integer, String>();
		WeakReference<Map<Integer, String>> myMap = new WeakReference<Map<Integer, String>>(map, referenceQueue);

		map = null;
		int i = 0;

		Thread t = new Thread(() -> {

			while (true) {

				try {

					Reference<? extends Object> reference = referenceQueue.remove(1000);

					if (reference != null) {
						System.out.println("############## Reference removed!");
					}

				} catch (Exception e) {
					e.printStackTrace();
				}
			}

		});
		t.start();

		while (true) {

			if (myMap != null && myMap.get() != null) {
				myMap.get().put(i++, "test" + i);
				System.out.println("im still working!!!!" + Runtime.getRuntime().freeMemory());
			} else {

				System.out.println("*******im free*******");
			}
		}
	}
}