Collection: Understanding WeakHashMap

[Barry Gaunt]

For the following example am I correct in saying that the assertion can fail,
because the WeakHashMap referenced by m2 could lose its contents, if there is some massive garbage collection taking place?

import java.util.*;
class WHM {
    class K {} // object for creating keys
    public static void main(String[] args) {
    
        Map m1 = new HashMap();
        Map m2 = new WeakHashMap(); // line 1
    
        WHM w = new WHM();
    
        K k1 = w.new K();
        K k2 = w.new K();
    
        m1.put(k1, "Item 1");
        m2.put(k2, "Item 1"); // line 2
        
        k1 = k2 = null; // line 3
    
/*
 * 
 * 
 * Later... assume that a massive garbage collection
 * is needed in this period
 * 
 * 
 */
        Iterator i;
        
        i = m1.keySet().iterator();
        while (i.hasNext()) {
            System.out.println((String)m1.get(i.next()));
        }
        assert !m2.isEmpty() : "m2 has lost it's contents"; // line 4
        
        i = m2.keySet().iterator();
        while (i.hasNext()) {
            System.out.println((String)m2.get(i.next()));
        }
    }
}  

Thanks
-Barry

[Thomas Paul]

Yes. if the WeakHashMap contains the only reference to an object, then that object is eligible for GC.