Java tutorial
import java.util.Map; import java.util.WeakHashMap; public class Weak { public static void main(String args[]) { final Map map = new WeakHashMap(); map.put(new String("Java2s"), "www.java2s.com"); Runnable runner = new Runnable() { public void run() { while (map.containsKey("Java2s")) { try { Thread.sleep(500); } catch (InterruptedException ignored) { } System.out.println("Waiting"); System.gc(); } } }; Thread t = new Thread(runner); t.start(); System.out.println("Main waiting"); try { t.join(); } catch (InterruptedException ignored) { } } }