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public interface Set<E>
A collection that contains no duplicates. In other words, for two set
elements e1 and e2, e1.equals(e2)
returns false. There
are additional stipulations on add
, equals
and hashCode
, as well as the requirements that constructors
do not permit duplicate elements. The Set interface is incompatible with
List; you cannot implement both simultaneously.
Note: Be careful about using mutable objects in sets. In particular, if a mutable object changes to become equal to another set element, you have violated the contract. As a special case of this, a Set is not allowed to be an element of itself, without risking undefined behavior.
Collection
,
List
,
SortedSet
,
HashSet
,
TreeSet
,
LinkedHashSet
,
AbstractSet
,
Collections.singleton(Object)
,
Collections.EMPTY_SET
Method Summary | ||
---|---|---|
boolean |
add(E o)
Adds the specified element to the set if it is not already present (optional operation). |
|
boolean |
addAll(Collection<? extends E> c)
Adds all of the elements of the given collection to this set (optional operation). |
|
void |
clear()
Removes all elements from this set (optional operation). |
|
boolean |
contains(Object o)
Returns true if the set contains the specified element. |
|
boolean |
containsAll(Collection<?> c)
Returns true if this set contains all elements in the specified collection. |
|
boolean |
equals(Object o)
Compares the specified object to this for equality. |
|
int |
hashCode()
Returns the hash code for this set. |
|
boolean |
isEmpty()
Returns true if the set contains no elements. |
|
Iterator<E> |
iterator()
Returns an iterator over the set. |
|
boolean |
remove(Object o)
Removes the specified element from this set (optional operation). |
|
boolean |
removeAll(Collection<?> c)
Removes from this set all elements contained in the specified collection (optional operation). |
|
boolean |
retainAll(Collection<?> c)
Retains only the elements in this set that are also in the specified collection (optional operation). |
|
int |
size()
Returns the number of elements in the set. |
|
Object[] |
toArray()
Returns an array containing the elements of this set. |
|
|
toArray(T[] a)
Returns an array containing the elements of this set, of the same runtime type of the argument. |
Method Detail |
---|
boolean add(E o)
o == null ? e == null : o.equals(e)
. Sets need not permit
all values, and may document what exceptions will be thrown if
a value is not permitted.
add
in interface Collection<E>
o
- the object to add
UnsupportedOperationException
- if this operation is not allowed
ClassCastException
- if the class of o prevents it from being added
IllegalArgumentException
- if some aspect of o prevents it from
being added
NullPointerException
- if null is not permitted in this setboolean addAll(Collection<? extends E> c)
addAll
in interface Collection<E>
c
- the collection to add
UnsupportedOperationException
- if this operation is not allowed
ClassCastException
- if the class of an element prevents it from
being added
IllegalArgumentException
- if something about an element prevents
it from being added
NullPointerException
- if null is not permitted in this set, or
if the argument c is nulladd(Object)
void clear()
clear
in interface Collection<E>
UnsupportedOperationException
- if this operation is not allowedboolean contains(Object o)
o == null ? e == null : o.equals(e)
.
contains
in interface Collection<E>
o
- the object to look for
ClassCastException
- if the type of o is not a valid type
for this set.
NullPointerException
- if o is null and this set doesn't
support null values.boolean containsAll(Collection<?> c)
containsAll
in interface Collection<E>
c
- the collection to check membership in
NullPointerException
- if c is null
ClassCastException
- if the type of any element in c is not
a valid type for this set.
NullPointerException
- if some element of c is null and this
set doesn't support null values.contains(Object)
boolean equals(Object o)
equals
in interface Collection<E>
equals
in class Object
o
- the object to compare to
Object.hashCode()
int hashCode()
hashCode
in interface Collection<E>
hashCode
in class Object
equals(Object)
boolean isEmpty()
isEmpty
in interface Collection<E>
Iterator<E> iterator()
iterator
in interface Collection<E>
iterator
in interface Iterable<E>
boolean remove(Object o)
o == null ? e == null : o.equals(e)
,
it is removed from the set.
remove
in interface Collection<E>
o
- the object to remove
UnsupportedOperationException
- if this operation is not allowed
ClassCastException
- if the type of o is not a valid type
for this set.
NullPointerException
- if o is null and this set doesn't allow
the removal of a null value.boolean removeAll(Collection<?> c)
removeAll
in interface Collection<E>
c
- the collection to remove from this set
UnsupportedOperationException
- if this operation is not allowed
NullPointerException
- if c is null
ClassCastException
- if the type of any element in c is not
a valid type for this set.
NullPointerException
- if some element of c is null and this
set doesn't support removing null values.remove(Object)
boolean retainAll(Collection<?> c)
retainAll
in interface Collection<E>
c
- the collection to keep
UnsupportedOperationException
- if this operation is not allowed
NullPointerException
- if c is null
ClassCastException
- if the type of any element in c is not
a valid type for this set.
NullPointerException
- if some element of c is null and this
set doesn't support retaining null values.remove(Object)
int size()
size
in interface Collection<E>
Object[] toArray()
toArray
in interface Collection<E>
toArray(Object[])
<T> T[] toArray(T[] a)
toArray
in interface Collection<E>
a
- the array to determine the return type; if it is big enough
it is used and returned
ArrayStoreException
- if the runtime type of a is not a supertype
of all elements in the set
NullPointerException
- if a is nulltoArray()
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