import java.lang.ref.WeakReference;import java.util.Iterator;import java.util.Map;import java.util.WeakHashMap;public class Main { public static void main(String[] argv) throws Exception { Object keyObject = ""; Object valueObject = ""; Map weakMap = new WeakHashMap(); weakMap.put(keyObject, valueObject); WeakReference weakValue = new WeakReference(valueObject); weakMap.put(keyObject, weakValue); Iterator it = weakMap.keySet().iterator(); while (it.hasNext()) { Object key = it.next(); weakValue = (WeakReference) weakMap.get(key); if (weakValue == null) { System.out.println("Value has been garbage-collected"); } else { System.out.println("Get value"); valueObject = weakValue.get(); } } }}