All Implemented Interfaces:
e1.equals(e2), and at most one null element. As implied by its name, this interface models the mathematical set abstraction.
The Set interface places additional stipulations, beyond those inherited from the Collection interface, on the contracts of all constructors and on the contracts of the add, equals and hashCode methods. Declarations for other inherited methods are also included here for convenience. (The specifications accompanying these declarations have been tailored to the Set interface, but they do not contain any additional stipulations.)
The additional stipulation on constructors is, not surprisingly, that all constructors must create a set that contains no duplicate elements (as defined above).
Note: Great care must be exercised if mutable objects are used as set elements. The behavior of a set is not specified if the value of an object is changed in a manner that affects equals comparisons while the object is an element in the set. A special case of this prohibition is that it is not permissible for a set to contain itself as an element.
Some set implementations have restrictions on the elements that they may contain. For example, some implementations prohibit null elements, and some have restrictions on the types of their elements. Attempting to add an ineligible element throws an unchecked exception, typically NullPointerException or ClassCastException. Attempting to query the presence of an ineligible element may throw an exception, or it may simply return false; some implementations will exhibit the former behavior and some will exhibit the latter. More generally, attempting an operation on an ineligible element whose completion would not result in the insertion of an ineligible element into the set may throw an exception or it may succeed, at the option of the implementation. Such exceptions are marked as "optional" in the specification for this interface.
This interface is a member of the Java Collections Framework.
- the type of elements maintained by this set
|Method from java.util.Set Summary:|
|add, addAll, clear, contains, containsAll, equals, hashCode, isEmpty, iterator, remove, removeAll, retainAll, size, toArray, toArray|
|Method from java.util.Set Detail:|
public boolean add(E e)
The stipulation above does not imply that sets must accept all elements; sets may refuse to add any particular element, including null, and throw an exception, as described in the specification for Collection.add . Individual set implementations should clearly document any restrictions on the elements that they may contain.
public boolean addAll(Collection<? extends E> c)
public void clear()
public boolean containsAll(Collection<?> c)
public int hashCode()
public boolean isEmpty()
public Iterator<E> iterator()
public boolean removeAll(Collection<?> c)
public boolean retainAll(Collection<?> c)
public int size()
The returned array will be "safe" in that no references to it are maintained by this set. (In other words, this method must allocate a new array even if this set is backed by an array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based APIs.
public T toArray(T a)
If this set fits in the specified array with room to spare (i.e., the array has more elements than this set), the element in the array immediately following the end of the set is set to null. (This is useful in determining the length of this set only if the caller knows that this set does not contain any null elements.)
If this set makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.
Like the #toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.
Suppose x is a set known to contain only strings. The following code can be used to dump the set into a newly allocated array of String:
String y = x.toArray(new String);Note that toArray(new Object) is identical in function to toArray().