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import java.util.HashMap;

public class ObjectPreserver implements Runnable {
  private static ObjectPreserver lifeLine = new ObjectPreserver();

  private ObjectPreserver() {
    Thread thread = new Thread( this);
    thread.setDaemon( true);
    thread.start(); // keep this object alive
  }
 
  // Neither this class, nor HashSet will be garbage collected.
  // References from HashMap to other objects will also exhibit this property
  private static final HashMap<IntegerConcurrentHashMap<Integer,Object> protectedMap 
    = new HashMap<IntegerConcurrentHashMap<Integer,Object>();
  
  public synchronized void run(){
    try {
      wait();
    } catch(InterruptedException e) { /* Forward to handler */ }
  }

  // Objects passed to this method will be preserved until
  // the unpreserveObject method is called
  public static void preserveObject(Object obj) {    
    protectedMap.put(0, obj);  
  }
  
  // Returns the same instance every time
  public static Object getObject() {
    return protectedMap.get(0);	  
  }
  
  // Unprotect the objects so that they can be garbage collected
  public static void unpreserveObject() {
    protectedMap.remove(0);
  }
}