Java tutorial
import java.util.Map; import java.util.WeakHashMap; public class Main { public static void main(String args[]) { final Map<String, String> map = new WeakHashMap<String, String>(); map.put(new String("A"), "B"); Runnable runner = new Runnable() { public void run() { while (map.containsKey("A")) { try { Thread.sleep(500); } catch (InterruptedException ignored) { } System.gc(); } } }; Thread t = new Thread(runner); t.start(); try { t.join(); } catch (InterruptedException ignored) { } } }