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

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Package java.util

Class java.util.IdentityHashMap

Examples of java.util.IdentityHashMap.entrySet()

java.util.IdentityHashMap.entrySet()
Returns a {@link Set} view of the mappings contained in this map.Each element in the returned set is a reference-equality-based Map.Entry. 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.
Like the backing map, the Map.Entry objects in the set returned by this method define key and value equality as reference-equality rather than object-equality. This affects the behavior of the equals and hashCode methods of these Map.Entry objects. A reference-equality based Map.Entry e is equal to an object o if and only if o is a Map.Entry and e.getKey()==o.getKey() && e.getValue()==o.getValue(). To accommodate these equals semantics, the hashCode method returns System.identityHashCode(e.getKey()) ^ System.identityHashCode(e.getValue()).
Owing to the reference-equality-based semantics of the Map.Entry instances in the set returned by this method, it is possible that the symmetry and transitivity requirements of the {@link Object#equals(Object)} contract may be violated if any ofthe entries in the set is compared to a normal map entry, or if the set returned by this method is compared to a set of normal map entries (such as would be returned by a call to this method on a normal map). However, the Object.equals contract is guaranteed to hold among identity-based map entries, and among sets of such entries. @return a set view of the identity-mappings contained in this map

    map.put("a key", null);
    map.put("another key", null);


    Set keyset = map.keySet();
    Collection valueset = map.values();
    Set entries = map.entrySet();
    Iterator it = entries.iterator();
    while (it.hasNext()) {
      Map.Entry entry = (Map.Entry) it.next();
      assertTrue("EntrySetIterator can not find entry ", entries
          .contains(entry));

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  public void test_entrySet_removeAll() {
    IdentityHashMap map = new IdentityHashMap();
    for (int i = 0; i < 1000; i++) {
      map.put(new Integer(i), new Integer(i));
    }
    Set set = map.entrySet();


    set.removeAll(set);
    assertEquals("did not remove all elements in the map", 0, map.size());
    assertTrue("did not remove all elements in the entryset", set.isEmpty());

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    map.put("a key", null);
    map.put("another key", null);


    Set keyset = map.keySet();
    Collection valueset = map.values();
    Set entries = map.entrySet();
    Iterator it = entries.iterator();
    while (it.hasNext()) {
      Map.Entry entry = (Map.Entry) it.next();
      assertTrue("EntrySetIterator can not find entry ", entries
          .contains(entry));

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  public void test_entrySet_removeAll() {
    IdentityHashMap map = new IdentityHashMap();
    for (int i = 0; i < 1000; i++) {
      map.put(new Integer(i), new Integer(i));
    }
    Set set = map.entrySet();


    set.removeAll(set);
    assertEquals("did not remove all elements in the map", 0, map.size());
    assertTrue("did not remove all elements in the entryset", set.isEmpty());

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