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Class AbstractCollection<E>
java.util.AbstractCollection<E>
All Implemented Interfaces:
Direct Known Subclasses:
public abstract class AbstractCollection<E>
This class provides a skeletal implementation of the
Collection
interface, to minimize the effort required to implement this interface.
To implement an unmodifiable collection, the programmer needs only to
extend this class and provide implementations for the iterator and
size methods. (The iterator returned by the iterator
method must implement hasNext and next.)
To implement a modifiable collection, the programmer must additionally
override this class's add method (which otherwise throws an
UnsupportedOperationException), and the iterator returned by the
iterator method must additionally implement its remove
method.
The programmer should generally provide a void (no argument) and
Collection constructor, as per the recommendation in the
Collection interface specification.
The documentation for each non-abstract method in this class describes its
implementation in detail. Each of these methods may be overridden if
the collection being implemented admits a more efficient implementation.
This class is a member of the
Java Collections Framework.
Since:
1.2
Author:
Josh Bloch, Neal Gafter
See Also:
Constructor Summary |
protected |
Sole constructor.
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Method Summary |
boolean |
Ensures that this collection contains the specified element (optional
operation).
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boolean |
Adds all of the elements in the specified collection to this collection
(optional operation).
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void |
Removes all of the elements from this collection (optional operation).
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boolean |
Returns true if this collection contains the specified element.
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boolean |
Returns true if this collection contains all of the elements
in the specified collection.
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boolean |
Returns true if this collection contains no elements.
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Returns an iterator over the elements contained in this collection.
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boolean |
Removes a single instance of the specified element from this
collection, if it is present (optional operation).
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boolean |
Removes all of this collection's elements that are also contained in the
specified collection (optional operation).
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boolean |
Retains only the elements in this collection that are contained in the
specified collection (optional operation).
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abstract int |
Returns the number of elements in this collection.
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Returns an array containing all of the elements in this collection.
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Returns an array containing all of the elements in this collection;
the runtime type of the returned array is that of the specified array.
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Returns a string representation of this collection.
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Methods inherited from class java.lang. Object |
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Methods inherited from interface java.util. Collection |
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Methods inherited from interface java.lang. Iterable |
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protected AbstractCollection |
() |
Sole constructor. (For invocation by subclass constructors, typically
implicit.)
Returns an iterator over the elements contained in this collection.
Specified by:
Returns:
an iterator over the elements contained in this collection
public abstract int size |
() |
Returns the number of elements in this collection. If this collection
contains more than Integer.MAX_VALUE elements, returns
Integer.MAX_VALUE.
Specified by:
Returns:
the number of elements in this collection
public boolean isEmpty |
() |
Returns
true if this collection contains no elements.
Implementation Requirements:
This implementation returns size() == 0.
Specified by:
Returns:
true if this collection contains no elements
Returns
true if this collection contains the specified element.
More formally, returns
true if and only if this collection
contains at least one element
e such that
Objects.equals(o, e).
Implementation Requirements:
This implementation iterates over the elements in the collection,
checking each element in turn for equality with the specified element.
Specified by:
Parameters:
o - element whose presence in this collection is to be tested
Returns:
true if this collection contains the specified
element
Throws:
Returns an array containing all of the elements in this collection.
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. The returned array's
runtime component type is
Object.
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.
Implementation Requirements:
This implementation returns an array containing all the elements
returned by this collection's iterator, in the same order, stored in
consecutive elements of the array, starting with index
0.
The length of the returned array is equal to the number of elements
returned by the iterator, even if the size of this collection changes
during iteration, as might happen if the collection permits
concurrent modification during iteration. The
size method is
called only as an optimization hint; the correct result is returned
even if the iterator returns a different number of elements.
This method is equivalent to:
List<E> list = new ArrayList<E>(size());
for (E e : this)
list.add(e);
return list.toArray();
Specified by:
Returns:
Returns an array containing all of the elements in this collection;
the runtime type of the returned array is that of the specified array.
If the collection fits in the specified array, it is returned therein.
Otherwise, a new array is allocated with the runtime type of the
specified array and the size of this 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.
Implementation Requirements:
This implementation returns an array containing all the elements
returned by this collection's iterator in the same order, stored in
consecutive elements of the array, starting with index
0.
If the number of elements returned by the iterator is too large to
fit into the specified array, then the elements are returned in a
newly allocated array with length equal to the number of elements
returned by the iterator, even if the size of this collection
changes during iteration, as might happen if the collection permits
concurrent modification during iteration. The
size method is
called only as an optimization hint; the correct result is returned
even if the iterator returns a different number of elements.
This method is equivalent to:
List<E> list = new ArrayList<E>(size());
for (E e : this)
list.add(e);
return list.toArray(a);
Specified by:
Type Parameters:
T - the component type of the array to contain the collection
Parameters:
a - 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.
Returns:
an array containing all of the elements in this collection
Throws:
Ensures that this collection contains the specified element (optional
operation). Returns
true if this collection changed as a
result of the call. (Returns
false if this collection does
not permit duplicates and already contains the specified element.)
Collections that support this operation may place limitations on what
elements may be added to this collection. In particular, some
collections will refuse to add null elements, and others will
impose restrictions on the type of elements that may be added.
Collection classes should clearly specify in their documentation any
restrictions on what elements may be added.
If a collection refuses to add a particular element for any reason
other than that it already contains the element, it must throw
an exception (rather than returning false). This preserves
the invariant that a collection always contains the specified element
after this call returns.
Implementation Requirements:
This implementation always throws an
UnsupportedOperationException.
Specified by:
Parameters:
e - element whose presence in this collection is to be ensured
Returns:
true if this collection changed as a result of the
call
Throws:
Removes a single instance of the specified element from this
collection, if it is present (optional operation). More formally,
removes an element
e such that
Objects.equals(o, e), if
this collection contains one or more such elements. Returns
true if this collection contained the specified element (or
equivalently, if this collection changed as a result of the call).
Implementation Requirements:
This implementation iterates over the collection looking for the
specified element. If it finds the element, it removes the element
from the collection using the iterator's remove method.
Note that this implementation throws an
UnsupportedOperationException if the iterator returned by this
collection's iterator method does not implement the remove
method and this collection contains the specified object.
Specified by:
Parameters:
o - element to be removed from this collection, if present
Returns:
true if an element was removed as a result of this call
Throws:
public boolean containsAll |
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Returns
true if this collection contains all of the elements
in the specified collection.
Implementation Requirements:
This implementation iterates over the specified collection,
checking each element returned by the iterator in turn to see
if it's contained in this collection. If all elements are so
contained true is returned, otherwise false.
Specified by:
Parameters:
c - collection to be checked for containment in this collection
Returns:
true if this collection contains all of the elements
in the specified collection
Throws:
ClassCastException - if the types of one or more elements
in the specified collection are incompatible with this
collection
(
optional)
NullPointerException - if the specified collection contains one
or more null elements and this collection does not permit null
elements
(
optional),
or if the specified collection is null.
See Also:
Adds all of the elements in the specified collection to this collection
(optional operation). The behavior of this operation is undefined if
the specified collection is modified while the operation is in progress.
(This implies that the behavior of this call is undefined if the
specified collection is this collection, and this collection is
nonempty.)
Implementation Requirements:
This implementation iterates over the specified collection, and adds
each object returned by the iterator to this collection, in turn.
Note that this implementation will throw an
UnsupportedOperationException unless add is
overridden (assuming the specified collection is non-empty).
Specified by:
Parameters:
c - collection containing elements to be added to this collection
Returns:
true if this collection changed as a result of the call
Throws:
UnsupportedOperationException - if the
addAll operation
is not supported by this collection
ClassCastException - if the class of an element of the specified
collection prevents it from being added to this collection
NullPointerException - if the specified collection contains a
null element and this collection does not permit null elements,
or if the specified collection is null
IllegalArgumentException - if some property of an element of the
specified collection prevents it from being added to this
collection
See Also:
Removes all of this collection's elements that are also contained in the
specified collection (optional operation). After this call returns,
this collection will contain no elements in common with the specified
collection.
Implementation Requirements:
This implementation iterates over this collection, checking each
element returned by the iterator in turn to see if it's contained
in the specified collection. If it's so contained, it's removed from
this collection with the iterator's
remove method.
Note that this implementation will throw an
UnsupportedOperationException if the iterator returned by the
iterator method does not implement the remove method
and this collection contains one or more elements in common with the
specified collection.
Specified by:
Parameters:
c - collection containing elements to be removed from this collection
Returns:
true if this collection changed as a result of the
call
Throws:
See Also:
Retains only the elements in this collection that are contained in the
specified collection (optional operation). In other words, removes from
this collection all of its elements that are not contained in the
specified collection.
Implementation Requirements:
This implementation iterates over this collection, checking each
element returned by the iterator in turn to see if it's contained
in the specified collection. If it's not so contained, it's removed
from this collection with the iterator's
remove method.
Note that this implementation will throw an
UnsupportedOperationException if the iterator returned by the
iterator method does not implement the remove method
and this collection contains one or more elements not present in the
specified collection.
Specified by:
Parameters:
c - collection containing elements to be retained in this collection
Returns:
true if this collection changed as a result of the call
Throws:
UnsupportedOperationException - if the
retainAll operation
is not supported by this collection
ClassCastException - if the types of one or more elements
in this collection are incompatible with the specified
collection
(
optional)
NullPointerException - if this collection contains one or more
null elements and the specified collection does not permit null
elements
(
optional),
or if the specified collection is null
See Also:
Removes all of the elements from this collection (optional operation).
The collection will be empty after this method returns.
Implementation Requirements:
This implementation iterates over this collection, removing each
element using the
Iterator.remove operation. Most
implementations will probably choose to override this method for
efficiency.
Note that this implementation will throw an
UnsupportedOperationException if the iterator returned by this
collection's iterator method does not implement the
remove method and this collection is non-empty.
Specified by:
Throws:
Returns a string representation of this collection. The string
representation consists of a list of the collection's elements in the
order they are returned by its iterator, enclosed in square brackets
(
"[]"). Adjacent elements are separated by the characters
", " (comma and space). Elements are converted to strings as
by
String.valueOf(Object).
Overrides:
Returns:
a string representation of this collection
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