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public interface Set
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(Object o)
Adds the specified element to the set if it is not already present (optional operation). |
boolean |
addAll(Collection 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 |
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. |
Object[] |
toArray(Object[] a)
Returns an array containing the elements of this set, of the same runtime type of the argument. |
Method Detail |
---|
boolean add(Object 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
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 c)
addAll
in interface Collection
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
UnsupportedOperationException
- if this operation is not allowedboolean contains(Object o)
o == null ? e == null : o.equals(e)
.
contains
in interface Collection
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
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
equals
in class Object
o
- the object to compare to
Object.hashCode()
int hashCode()
hashCode
in interface Collection
hashCode
in class Object
equals(Object)
boolean isEmpty()
isEmpty
in interface Collection
Iterator iterator()
iterator
in interface Collection
boolean remove(Object o)
o == null ? e == null : o.equals(e)
,
it is removed from the set.
remove
in interface Collection
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
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
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
Object[] toArray()
toArray
in interface Collection
toArray(Object[])
Object[] toArray(Object[] a)
toArray
in interface Collection
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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