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Class java.util.AbstractCollection

java.lang.Object
    |
    +----java.util.AbstractCollection

public abstract class AbstractCollection

extends Object

implements Collection

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 methods 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.

Since:

JDK1.2

See Also:

Collection

AbstractCollection()

add(Object)

Ensures that this Collection contains the specified element (optional operation).

addAll(Collection)

Adds all of the elements in the specified Collection to this Collection (optional operation).

clear()

Removes all of the elements from this Collection (optional operation).

contains(Object)

Returns true if this Collection contains the specified element.

containsAll(Collection)

Returns true if this Collection contains all of the elements in the specified Collection.

isEmpty()

Returns true if this Collection contains no elements.

iterator()

Returns an Iterator over the elements contained in this Collection.

remove(Object)

Removes a single instance of the specified element from this Collection, if it is present (optional operation).

removeAll(Collection)

Removes from this Collection all of its elements that are contained in the specified Collection (optional operation).

retainAll(Collection)

Retains only the elements in this Collection that are contained in the specified Collection (optional operation).

size()

Returns the number of elements in this Collection.

toArray()

Returns an array containing all of the elements in this Collection.

toString()

Returns a string representation of this Collection, containing the String representation of each element.

public AbstractCollection()

public abstract Iterator iterator()

Returns an Iterator over the elements contained in this Collection.

public abstract int size()

Returns the number of elements in this Collection.

public boolean isEmpty()

Returns true if this Collection contains no elements. This implementation returns size() == 0.

public boolean contains(Object o)

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 (o==null ? e==null : o.equals(e)).

This implementation iterates over the elements in the Collection, checking each element in turn for equality with o.

public Object[] toArray()

Returns an array containing all of the elements in this Collection. If the 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 will be "safe" in that no references to it are maintained by the Collection. (In other words, this method must allocate a new array even if the Collection is backed by an Array). The caller is thus free to modify the returned array.

This implementation allocates the array to be returned, and iterates over the elements in the Collection, storing each object reference in the next consecutive element of the array, starting with element 0.

public boolean add(Object o)

Ensures that this Collection contains the specified element (optional operation). Returns true if the 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 the 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.

This implementation always throws an UnsupportedOperationException.

Parameters:

o - element whose presence in this Collection is to be ensured.

Returns:

true if the Collection changed as a result of the call.

Throws: UnsupportedOperationException

add is not supported by this Collection.

Throws: NullPointerException

this Collection does not permit null elements, and the specified element is null.

Throws: ClassCastException

class of the specified element prevents it from being added to this Collection.

Throws: IllegalArgumentException

some aspect of this element prevents it from being added to this Collection.

public boolean remove(Object o)

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 (o==null ? e==null : o.equals(e)), if the Collection contains one or more such elements. Returns true if the Collection contained the specified element (or equivalently, if the Collection changed as a result of the call).

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 will throw an UnsupportedOperationException if the Iterator returned by this Collection's iterator method does not implement the remove method.

Parameters:

o - element to be removed from this Collection, if present.

Returns:

true if the Collection contained the specified element.

Throws: UnsupportedOperationException

remove is not supported by this Collection.

public boolean containsAll(Collection c)

Returns true if this Collection contains all of the elements in the specified Collection.

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.

See Also:

contains

public boolean addAll(Collection c)

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 the specified Collection is this Collection, and this Collection is nonempty.)

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.

Throws: UnsupportedOperationException

addAll is not supported by this Collection.

See Also:

add

public boolean removeAll(Collection c)

Removes from this Collection all of its elements that are contained in the specified Collection (optional operation).

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 iterator does not implement the remove method.

Returns:

true if this Collection changed as a result of the call.

Throws: UnsupportedOperationException

removeAll is not supported by this Collection.

See Also:

remove, contains

public boolean retainAll(Collection c)

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.

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 iterator does not implement the remove method.

Returns:

true if this Collection changed as a result of the call.

Throws: UnsupportedOperationException

retainAll is not supported by this Collection.

See Also:

remove, contains

public void clear()

Removes all of the elements from this Collection (optional operation). The Collection will be empty after this call returns (unless it throws an exception).

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.

Throws: UnsupportedOperationException

remove is not supported by this Collection.

public String toString()

Returns a string representation of this Collection, containing the String representation of each element.

Overrides:

toString in class Object

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