public final class ArraySet<E> extends Object implements Collection<E>, Set<E>
HashSet
. The design is very similar to
ArrayMap
, with all of the caveats described there. This implementation is
separate from ArrayMap, however, so the Object array contains only one item for each
entry in the set (instead of a pair for a mapping).
Note that this implementation is not intended to be appropriate for data structures that may contain large numbers of items. It is generally slower than a traditional HashSet, since lookups require a binary search and adds and removes require inserting and deleting entries in the array. For containers holding up to hundreds of items, the performance difference is not significant, less than 50%.
Because this container is intended to better balance memory use, unlike most other standard Java containers it will shrink its array as items are removed from it. Currently you have no control over this shrinking -- if you set a capacity and then remove an item, it may reduce the capacity to better match the current size. In the future an explicit call to set the capacity should turn off this aggressive shrinking behavior.
Constructor and Description |
---|
ArraySet()
Create a new empty ArraySet.
|
ArraySet(ArraySet<E> set)
Create a new ArraySet with the mappings from the given ArraySet.
|
ArraySet(Collection<E> set) |
ArraySet(int capacity)
Create a new ArraySet with a given initial capacity.
|
ArraySet(int capacity,
boolean identityHashCode) |
Modifier and Type | Method and Description |
---|---|
boolean |
add(E value)
Adds the specified object to this set.
|
void |
addAll(ArraySet<? extends E> array)
Perform a
add(Object) of all values in array |
boolean |
addAll(Collection<? extends E> collection)
Perform an
add(Object) of all values in collection |
void |
append(E value)
Special fast path for appending items to the end of the array without validation.
|
void |
clear()
Make the array map empty.
|
boolean |
contains(Object key)
Check whether a value exists in the set.
|
boolean |
containsAll(Collection<?> collection)
Determine if the array set contains all of the values in the given collection.
|
void |
ensureCapacity(int minimumCapacity)
Ensure the array map can hold at least minimumCapacity
items.
|
boolean |
equals(Object object)
Indicates whether some other object is "equal to" this one.
|
int |
hashCode()
Returns a hash code value for the object.
|
int |
indexOf(Object key)
Returns the index of a value in the set.
|
boolean |
isEmpty()
Return true if the array map contains no items.
|
Iterator<E> |
iterator()
Return an
Iterator over all values in the set. |
boolean |
remove(Object object)
Removes the specified object from this set.
|
boolean |
removeAll(ArraySet<? extends E> array)
Perform a
remove(Object) of all values in array |
boolean |
removeAll(Collection<?> collection)
Remove all values in the array set that exist in the given collection.
|
E |
removeAt(int index)
Remove the key/value mapping at the given index.
|
boolean |
retainAll(Collection<?> collection)
Remove all values in the array set that do not exist in the given collection.
|
int |
size()
Return the number of items in this array map.
|
Object[] |
toArray()
Returns an array containing all of the elements in this collection.
|
<T> T[] |
toArray(T[] array)
Returns an array containing all of the elements in this collection;
the runtime type of the returned array is that of the specified array.
|
String |
toString()
Returns a string representation of the object.
|
E |
valueAt(int index)
Return the value at the given index in the array.
|
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
spliterator
parallelStream, removeIf, stream
public ArraySet()
public ArraySet(int capacity)
public ArraySet(int capacity, boolean identityHashCode)
public ArraySet(ArraySet<E> set)
public ArraySet(Collection<E> set)
public void clear()
public void ensureCapacity(int minimumCapacity)
public boolean contains(Object key)
public int indexOf(Object key)
key
- The value to search for.public E valueAt(int index)
index
- The desired index, must be between 0 and size()
-1.public boolean isEmpty()
public boolean add(E value)
add
in interface Collection<E>
add
in interface Set<E>
value
- the object to add.true
if this set is modified, false
otherwise.ClassCastException
- when the class of the object is inappropriate for this set.public void append(E value)
public void addAll(ArraySet<? extends E> array)
add(Object)
of all values in arrayarray
- The array whose contents are to be retrieved.public boolean remove(Object object)
public E removeAt(int index)
index
- The desired index, must be between 0 and size()
-1.public boolean removeAll(ArraySet<? extends E> array)
remove(Object)
of all values in arrayarray
- The array whose contents are to be removed.public int size()
public Object[] toArray()
Collection
The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection 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> T[] toArray(T[] array)
Collection
If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null. (This is useful in determining the length of this collection only if the caller knows that this collection does not contain any null elements.)
If this collection 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 Collection.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 collection known to contain only strings. The following code can be used to dump the collection into a newly allocated array of String:
String[] y = x.toArray(new String[0]);Note that toArray(new Object[0]) is identical in function to toArray().
toArray
in interface Collection<E>
toArray
in interface Set<E>
array
- the array into which the elements of this collection are to be
stored, if it is big enough; otherwise, a new array of the same
runtime type is allocated for this purpose.public boolean equals(Object object)
The equals
method implements an equivalence relation
on non-null object references:
x
, x.equals(x)
should return
true
.
x
and y
, x.equals(y)
should return true
if and only if
y.equals(x)
returns true
.
x
, y
, and z
, if
x.equals(y)
returns true
and
y.equals(z)
returns true
, then
x.equals(z)
should return true
.
x
and y
, multiple invocations of
x.equals(y)
consistently return true
or consistently return false
, provided no
information used in equals
comparisons on the
objects is modified.
x
,
x.equals(null)
should return false
.
The equals
method for class Object
implements
the most discriminating possible equivalence relation on objects;
that is, for any non-null reference values x
and
y
, this method returns true
if and only
if x
and y
refer to the same object
(x == y
has the value true
).
Note that it is generally necessary to override the hashCode
method whenever this method is overridden, so as to maintain the
general contract for the hashCode
method, which states
that equal objects must have equal hash codes.
This implementation returns false if the object is not a set, or if the sets have different sizes. Otherwise, for each value in this set, it checks to make sure the value also exists in the other set. If any value doesn't exist, the method returns false; otherwise, it returns true.
equals
in interface Collection<E>
equals
in interface Set<E>
equals
in class Object
object
- the reference object with which to compare.true
if this object is the same as the obj
argument; false
otherwise.Object.hashCode()
,
HashMap
public int hashCode()
HashMap
.
The general contract of hashCode
is:
hashCode
method
must consistently return the same integer, provided no information
used in equals
comparisons on the object is modified.
This integer need not remain consistent from one execution of an
application to another execution of the same application.
equals(Object)
method, then calling the hashCode
method on each of
the two objects must produce the same integer result.
Object.equals(java.lang.Object)
method, then calling the hashCode
method on each of the
two objects must produce distinct integer results. However, the
programmer should be aware that producing distinct integer results
for unequal objects may improve the performance of hash tables.
As much as is reasonably practical, the hashCode method defined by
class Object
does return distinct integers for distinct
objects. (This is typically implemented by converting the internal
address of the object into an integer, but this implementation
technique is not required by the
JavaTM programming language.)
hashCode
in interface Collection<E>
hashCode
in interface Set<E>
hashCode
in class Object
Object.equals(java.lang.Object)
,
System.identityHashCode(java.lang.Object)
public String toString()
toString
method returns a string that
"textually represents" this object. The result should
be a concise but informative representation that is easy for a
person to read.
It is recommended that all subclasses override this method.
The toString
method for class Object
returns a string consisting of the name of the class of which the
object is an instance, the at-sign character `@
', and
the unsigned hexadecimal representation of the hash code of the
object. In other words, this method returns a string equal to the
value of:
getClass().getName() + '@' + Integer.toHexString(hashCode())
This implementation composes a string by iterating over its values. If this set contains itself as a value, the string "(this Set)" will appear in its place.
public Iterator<E> iterator()
Iterator
over all values in the set.
Note: this is a fairly inefficient way to access the array contents, it requires generating a number of temporary objects and allocates additional state information associated with the container that will remain for the life of the container.
public boolean containsAll(Collection<?> collection)
containsAll
in interface Collection<E>
containsAll
in interface Set<E>
collection
- The collection whose contents are to be checked against.Collection.contains(Object)
public boolean addAll(Collection<? extends E> collection)
add(Object)
of all values in collectionaddAll
in interface Collection<E>
addAll
in interface Set<E>
collection
- The collection whose contents are to be retrieved.Collection.add(Object)
public boolean removeAll(Collection<?> collection)
removeAll
in interface Collection<E>
removeAll
in interface Set<E>
collection
- The collection whose contents are to be used to remove values.Collection.remove(Object)
,
Collection.contains(Object)
public boolean retainAll(Collection<?> collection)
retainAll
in interface Collection<E>
retainAll
in interface Set<E>
collection
- The collection whose contents are to be used to determine which
values to keep.Collection.remove(Object)
,
Collection.contains(Object)