Examples of java.util.IdentityHashMap.keySet() | massapi.com

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Package java.util

Class java.util.IdentityHashMap

Examples of java.util.IdentityHashMap.keySet()

java.util.IdentityHashMap.keySet()
Returns an identity-based set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. If the map is modified while an iteration over the set is in progress, the results of the iteration are undefined. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear methods. It does not support the add or addAll methods.
While the object returned by this method implements the Set interface, it does not obey Set's general contract. Like its backing map, the set returned by this method defines element equality as reference-equality rather than object-equality. This affects the behavior of its contains, remove, containsAll, equals, and hashCode methods.
The equals method of the returned set returns true only if the specified object is a set containing exactly the same object references as the returned set. The symmetry and transitivity requirements of the Object.equals contract may be violated if the set returned by this method is compared to a normal set. However, the Object.equals contract is guaranteed to hold among sets returned by this method.
The hashCode method of the returned set returns the sum of the identity hashcodes of the elements in the set, rather than the sum of their hashcodes. This is mandated by the change in the semantics of the equals method, in order to enforce the general contract of the Object.hashCode method among sets returned by this method. @return an identity-based set view of the keys contained in this map @see Object#equals(Object) @see System#identityHashCode(Object)


    Map map = new IdentityHashMap(101);
    map.put(new Integer(1), "1");
    map.put(new Integer(102), "102");
    map.put(new Integer(203), "203");
    Iterator it = map.keySet().iterator();
    Integer remove1 = (Integer) it.next();
    it.hasNext();
    it.remove();
    Integer remove2 = (Integer) it.next();
    it.remove();

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        new Integer(1), new Integer(102), new Integer(203) }));
    list.remove(remove1);
    list.remove(remove2);
    assertTrue("Wrong result", it.next().equals(list.get(0)));
    assertEquals("Wrong size", 1, map.size());
    assertTrue("Wrong contents", map.keySet().iterator().next().equals(
        list.get(0)));


    Map map2 = new IdentityHashMap(101);
    map2.put(new Integer(1), "1");
    map2.put(new Integer(4), "4");

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        list.get(0)));


    Map map2 = new IdentityHashMap(101);
    map2.put(new Integer(1), "1");
    map2.put(new Integer(4), "4");
    Iterator it2 = map2.keySet().iterator();
    Integer remove3 = (Integer) it2.next();
    Integer next;
    if (remove3.intValue() == 1)
      next = new Integer(4);
    else

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      next = new Integer(1);
    it2.hasNext();
    it2.remove();
    assertTrue("Wrong result 2", it2.next().equals(next));
    assertEquals("Wrong size 2", 1, map2.size());
    assertTrue("Wrong contents 2", map2.keySet().iterator().next().equals(
        next));
  }


  /**
   * @tests java.util.IdentityHashMap#put(java.lang.Object, java.lang.Object)

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