java.util
Class AbstractCollection<E>

java.lang.Object sample code for java.lang.Object definition code for java.lang.Object 
  extended by java.util.AbstractCollection<E>
All Implemented Interfaces:
Iterable sample code for java.lang.Iterable definition code for java.lang.Iterable <E>, Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Direct Known Subclasses:
AbstractList sample code for java.util.AbstractList definition code for java.util.AbstractList , AbstractQueue sample code for java.util.AbstractQueue definition code for java.util.AbstractQueue , AbstractSet sample code for java.util.AbstractSet definition code for java.util.AbstractSet

public abstract class AbstractCollection<E>
extends Object sample code for java.lang.Object definition code for java.lang.Object
implements Collection sample code for java.util.Collection definition code for java.util.Collection <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 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.

This class is a member of the Java Collections Framework.

Since:
1.2
See Also:
Collection sample code for java.util.Collection definition code for java.util.Collection

Constructor Summary
protected AbstractCollection sample code for java.util.AbstractCollection.AbstractCollection() definition code for java.util.AbstractCollection.AbstractCollection() ()
          Sole constructor.
 
Method Summary
 boolean add sample code for java.util.AbstractCollection.add(E) definition code for java.util.AbstractCollection.add(E) (E o)
          Ensures that this collection contains the specified element (optional operation).
 boolean addAll sample code for java.util.AbstractCollection.addAll(java.util.Collection) definition code for java.util.AbstractCollection.addAll(java.util.Collection) (Collection sample code for java.util.Collection definition code for java.util.Collection <? extends E> c)
          Adds all of the elements in the specified collection to this collection (optional operation).
 void clear sample code for java.util.AbstractCollection.clear() definition code for java.util.AbstractCollection.clear() ()
          Removes all of the elements from this collection (optional operation).
 boolean contains sample code for java.util.AbstractCollection.contains(java.lang.Object) definition code for java.util.AbstractCollection.contains(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  o)
          Returns true if this collection contains the specified element.
 boolean containsAll sample code for java.util.AbstractCollection.containsAll(java.util.Collection) definition code for java.util.AbstractCollection.containsAll(java.util.Collection) (Collection sample code for java.util.Collection definition code for java.util.Collection <?> c)
          Returns true if this collection contains all of the elements in the specified collection.
 boolean isEmpty sample code for java.util.AbstractCollection.isEmpty() definition code for java.util.AbstractCollection.isEmpty() ()
          Returns true if this collection contains no elements.
abstract  Iterator sample code for java.util.Iterator definition code for java.util.Iterator <E> iterator sample code for java.util.AbstractCollection.iterator() definition code for java.util.AbstractCollection.iterator() ()
          Returns an iterator over the elements contained in this collection.
 boolean remove sample code for java.util.AbstractCollection.remove(java.lang.Object) definition code for java.util.AbstractCollection.remove(java.lang.Object) (Object sample code for java.lang.Object definition code for java.lang.Object  o)
          Removes a single instance of the specified element from this collection, if it is present (optional operation).
 boolean removeAll sample code for java.util.AbstractCollection.removeAll(java.util.Collection) definition code for java.util.AbstractCollection.removeAll(java.util.Collection) (Collection sample code for java.util.Collection definition code for java.util.Collection <?> c)
          Removes from this collection all of its elements that are contained in the specified collection (optional operation).
 boolean retainAll sample code for java.util.AbstractCollection.retainAll(java.util.Collection) definition code for java.util.AbstractCollection.retainAll(java.util.Collection) (Collection sample code for java.util.Collection definition code for java.util.Collection <?> c)
          Retains only the elements in this collection that are contained in the specified collection (optional operation).
abstract  int size sample code for java.util.AbstractCollection.size() definition code for java.util.AbstractCollection.size() ()
          Returns the number of elements in this collection.
 Object sample code for java.lang.Object definition code for java.lang.Object [] toArray sample code for java.util.AbstractCollection.toArray() definition code for java.util.AbstractCollection.toArray() ()
          Returns an array containing all of the elements in this collection.
<T> T[]
toArray sample code for java.util.AbstractCollection.toArray(T[]) definition code for java.util.AbstractCollection.toArray(T[]) (T[] a)
          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 sample code for java.lang.String definition code for java.lang.String toString sample code for java.util.AbstractCollection.toString() definition code for java.util.AbstractCollection.toString() ()
          Returns a string representation of this collection.
 
Methods inherited from class java.lang.Object sample code for java.lang.Object definition code for java.lang.Object
clone sample code for java.lang.Object.clone() definition code for java.lang.Object.clone() , equals sample code for java.lang.Object.equals(java.lang.Object) definition code for java.lang.Object.equals(java.lang.Object) , finalize sample code for java.lang.Object.finalize() definition code for java.lang.Object.finalize() , getClass sample code for java.lang.Object.getClass() definition code for java.lang.Object.getClass() , hashCode sample code for java.lang.Object.hashCode() definition code for java.lang.Object.hashCode() , notify sample code for java.lang.Object.notify() definition code for java.lang.Object.notify() , notifyAll sample code for java.lang.Object.notifyAll() definition code for java.lang.Object.notifyAll() , wait sample code for java.lang.Object.wait() definition code for java.lang.Object.wait() , wait sample code for java.lang.Object.wait(long) definition code for java.lang.Object.wait(long) , wait sample code for java.lang.Object.wait(long, int) definition code for java.lang.Object.wait(long, int)
 
Methods inherited from interface java.util.Collection sample code for java.util.Collection definition code for java.util.Collection
equals sample code for java.util.Collection.equals(java.lang.Object) definition code for java.util.Collection.equals(java.lang.Object) , hashCode sample code for java.util.Collection.hashCode() definition code for java.util.Collection.hashCode()
 

Constructor Detail

AbstractCollection sample code for java.util.AbstractCollection() definition code for java.util.AbstractCollection()

protected AbstractCollection()
Sole constructor. (For invocation by subclass constructors, typically implicit.)

Method Detail

iterator sample code for java.util.AbstractCollection.iterator() definition code for java.util.AbstractCollection.iterator()

public abstract Iterator sample code for java.util.Iterator definition code for java.util.Iterator <E> iterator()
Returns an iterator over the elements contained in this collection.

Specified by:
iterator sample code for java.lang.Iterable.iterator() definition code for java.lang.Iterable.iterator() in interface Iterable sample code for java.lang.Iterable definition code for java.lang.Iterable <E>
Specified by:
iterator sample code for java.util.Collection.iterator() definition code for java.util.Collection.iterator() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Returns:
an iterator over the elements contained in this collection.

size sample code for java.util.AbstractCollection.size() definition code for java.util.AbstractCollection.size()

public abstract int size()
Returns the number of elements in this collection. If the collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Specified by:
size sample code for java.util.Collection.size() definition code for java.util.Collection.size() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Returns:
the number of elements in this collection.

isEmpty sample code for java.util.AbstractCollection.isEmpty() definition code for java.util.AbstractCollection.isEmpty()

public boolean isEmpty()
Returns true if this collection contains no elements.

This implementation returns size() == 0.

Specified by:
isEmpty sample code for java.util.Collection.isEmpty() definition code for java.util.Collection.isEmpty() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Returns:
true if this collection contains no elements.

contains sample code for java.util.AbstractCollection.contains(java.lang.Object) definition code for java.util.AbstractCollection.contains(java.lang.Object)

public boolean contains(Object sample code for java.lang.Object definition code for java.lang.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 the specified element.

Specified by:
contains sample code for java.util.Collection.contains(java.lang.Object) definition code for java.util.Collection.contains(java.lang.Object) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
o - object to be checked for containment in this collection.
Returns:
true if this collection contains the specified element.

toArray sample code for java.util.AbstractCollection.toArray() definition code for java.util.AbstractCollection.toArray()

public Object sample code for java.lang.Object definition code for java.lang.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.

Specified by:
toArray sample code for java.util.Collection.toArray() definition code for java.util.Collection.toArray() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Returns:
an array containing all of the elements in this collection.

toArray sample code for java.util.AbstractCollection.<T>toArray(T[]) definition code for java.util.AbstractCollection.<T>toArray(T[])

public <T> T[] toArray(T[] a)
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 the collection fits in the specified array with room to spare (i.e., the array has more elements than the 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 the collection only if the caller knows that the 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.

This implementation checks if the array is large enough to contain the collection; if not, it allocates a new array of the correct size and type (using reflection). Then, it iterates over the collection, storing each object reference in the next consecutive element of the array, starting with element 0. If the array is larger than the collection, a null is stored in the first location after the end of the collection.

Specified by:
toArray sample code for java.util.Collection.toArray(T[]) definition code for java.util.Collection.toArray(T[]) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
a - the array into which the elements of the 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 the elements of the collection.
Throws:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified array is null.
ArrayStoreException sample code for java.lang.ArrayStoreException definition code for java.lang.ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this collection.

add sample code for java.util.AbstractCollection.add(E) definition code for java.util.AbstractCollection.add(E)

public boolean add(E 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.

Specified by:
add sample code for java.util.Collection.add(E) definition code for java.util.Collection.add(E) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
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 sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the add method is not supported by this collection.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if this collection does not permit null elements, and the specified element is null.
ClassCastException sample code for java.lang.ClassCastException definition code for java.lang.ClassCastException - if the class of the specified element prevents it from being added to this collection.
IllegalArgumentException sample code for java.lang.IllegalArgumentException definition code for java.lang.IllegalArgumentException - if some aspect of this element prevents it from being added to this collection.

remove sample code for java.util.AbstractCollection.remove(java.lang.Object) definition code for java.util.AbstractCollection.remove(java.lang.Object)

public boolean remove(Object sample code for java.lang.Object definition code for java.lang.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 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:
remove sample code for java.util.Collection.remove(java.lang.Object) definition code for java.util.Collection.remove(java.lang.Object) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
o - element to be removed from this collection, if present.
Returns:
true if the collection contained the specified element.
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the remove method is not supported by this collection.

containsAll sample code for java.util.AbstractCollection.containsAll(java.util.Collection<?>) definition code for java.util.AbstractCollection.containsAll(java.util.Collection<?>)

public boolean containsAll(Collection sample code for java.util.Collection definition code for java.util.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.

Specified by:
containsAll sample code for java.util.Collection.containsAll(java.util.Collection) definition code for java.util.Collection.containsAll(java.util.Collection) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
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:
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified collection is null.
See Also:
contains(Object) sample code for java.util.AbstractCollection.contains(java.lang.Object) definition code for java.util.AbstractCollection.contains(java.lang.Object)

addAll sample code for java.util.AbstractCollection.addAll(java.util.Collection<? extends E>) definition code for java.util.AbstractCollection.addAll(java.util.Collection<? extends E>)

public boolean addAll(Collection sample code for java.util.Collection definition code for java.util.Collection <? extends E> 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 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 (assuming the specified collection is non-empty).

Specified by:
addAll sample code for java.util.Collection.addAll(java.util.Collection) definition code for java.util.Collection.addAll(java.util.Collection) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
c - collection whose elements are to be added to this collection.
Returns:
true if this collection changed as a result of the call.
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if this collection does not support the addAll method.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified collection is null.
See Also:
add(Object) sample code for java.util.AbstractCollection.add(E) definition code for java.util.AbstractCollection.add(E)

removeAll sample code for java.util.AbstractCollection.removeAll(java.util.Collection<?>) definition code for java.util.AbstractCollection.removeAll(java.util.Collection<?>)

public boolean removeAll(Collection sample code for java.util.Collection definition code for java.util.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 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:
removeAll sample code for java.util.Collection.removeAll(java.util.Collection) definition code for java.util.Collection.removeAll(java.util.Collection) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
c - elements to be removed from this collection.
Returns:
true if this collection changed as a result of the call.
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the removeAll method is not supported by this collection.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified collection is null.
See Also:
remove(Object) sample code for java.util.AbstractCollection.remove(java.lang.Object) definition code for java.util.AbstractCollection.remove(java.lang.Object) , contains(Object) sample code for java.util.AbstractCollection.contains(java.lang.Object) definition code for java.util.AbstractCollection.contains(java.lang.Object)

retainAll sample code for java.util.AbstractCollection.retainAll(java.util.Collection<?>) definition code for java.util.AbstractCollection.retainAll(java.util.Collection<?>)

public boolean retainAll(Collection sample code for java.util.Collection definition code for java.util.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 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:
retainAll sample code for java.util.Collection.retainAll(java.util.Collection) definition code for java.util.Collection.retainAll(java.util.Collection) in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Parameters:
c - elements to be retained in this collection.
Returns:
true if this collection changed as a result of the call.
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the retainAll method is not supported by this Collection.
NullPointerException sample code for java.lang.NullPointerException definition code for java.lang.NullPointerException - if the specified collection is null.
See Also:
remove(Object) sample code for java.util.AbstractCollection.remove(java.lang.Object) definition code for java.util.AbstractCollection.remove(java.lang.Object) , contains(Object) sample code for java.util.AbstractCollection.contains(java.lang.Object) definition code for java.util.AbstractCollection.contains(java.lang.Object)

clear sample code for java.util.AbstractCollection.clear() definition code for java.util.AbstractCollection.clear()

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 and this collection is non-empty.

Specified by:
clear sample code for java.util.Collection.clear() definition code for java.util.Collection.clear() in interface Collection sample code for java.util.Collection definition code for java.util.Collection <E>
Throws:
UnsupportedOperationException sample code for java.lang.UnsupportedOperationException definition code for java.lang.UnsupportedOperationException - if the clear method is not supported by this collection.

toString sample code for java.util.AbstractCollection.toString() definition code for java.util.AbstractCollection.toString()

public String sample code for java.lang.String definition code for java.lang.String  toString()
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).

This implementation creates an empty string buffer, appends a left square bracket, and iterates over the collection appending the string representation of each element in turn. After appending each element except the last, the string ", " is appended. Finally a right bracket is appended. A string is obtained from the string buffer, and returned.

Overrides:
toString sample code for java.lang.Object.toString() definition code for java.lang.Object.toString() in class Object sample code for java.lang.Object definition code for java.lang.Object
Returns:
a string representation of this collection.