Even though, it is not public, using javap you can at least look at methods it implements:
Compiled from WeakConcurrentHashMap.java
public class weblogic.utils.collections.WeakConcurrentHashMap extends java.util.
AbstractMap implements java.util.Map, java.lang.Cloneable {
public weblogic.utils.collections.WeakConcurrentHashMap(int,float);
public weblogic.utils.collections.WeakConcurrentHashMap(int);
public weblogic.utils.collections.WeakConcurrentHashMap();
public weblogic.utils.collections.WeakConcurrentHashMap(java.util.Map);
public int size();
public boolean isEmpty();
public boolean containsValue(java.lang.Object);
public boolean containsKey(java.lang.Object);
public java.lang.Object get(java.lang.Object);
public java.lang.Object put(java.lang.Object, java.lang.Object);
public java.lang.Object remove(java.lang.Object);
public void putAll(java.util.Map);
public synchronized void clear();
public synchronized java.lang.Object clone();
public java.util.Set keySet();
public java.util.Collection values();
public java.util.Set entrySet();
int capacity();
float loadFactor();
static int access$000(weblogic.utils.collections.WeakConcurrentHashMap);
static weblogic.utils.collections.WeakConcurrentHashMap.Entry access$100(web
logic.utils.collections.WeakConcurrentHashMap)[];
static int access$010(weblogic.utils.collections.WeakConcurrentHashMap);
}