Class AbstractCollection<E>

java.lang.Object
java.util.AbstractCollection<E>
All Implemented Interfaces:
Iterable<E>, Collection<E>
Direct Known Subclasses:
AbstractList, AbstractQueue, AbstractSet, ArrayDeque
public abstract class AbstractCollection<E> extends Object implements Collection<E>

Class AbstractCollection is an abstract implementation of the Collection interface. A subclass must implement the abstract methods iterator() and size() to create an immutable collection. To create a modifiable collection it's necessary to override the add() method that currently throws an UnsupportedOperationException.

Since

1.2

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    protected
    AbstractCollection()
    Constructs a new instance of this AbstractCollection.

  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    add(E object)
    Attempts to add object to the contents of this Collection (optional).
    boolean
    addAll(Collection<? extends E> collection)
    Attempts to add all of the objects contained in collection to the contents of this Collection (optional).
    void
    clear()
    Removes all elements from this Collection, leaving it empty (optional).
    boolean
    contains(Object object)
    Tests whether this Collection contains the specified object.
    boolean
    containsAll(Collection<?> collection)
    Tests whether this Collection contains all objects contained in the specified Collection.
    boolean
    isEmpty()
    Returns if this Collection contains no elements.
    abstract Iterator<E>
    iterator()
    Returns an instance of Iterator that may be used to access the objects contained by this Collection.
    boolean
    remove(Object object)
    Removes one instance of the specified object from this Collection if one is contained (optional).
    boolean
    removeAll(Collection<?> collection)
    Removes all occurrences in this Collection of each object in the specified Collection (optional).
    boolean
    retainAll(Collection<?> collection)
    Removes all objects from this Collection that are not also found in the Collection passed (optional).
    abstract int
    size()
    Returns a count of how many objects this Collection contains.
    Object[]
    toArray()
    Returns a new array containing all elements contained in this ArrayList.
    <T> T[]
    toArray(T[] contents)
    Returns an array containing all elements contained in this ArrayList.
    String
    toString()
    Returns the string representation of this Collection.

    Methods inherited from class Object

    clone, equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

    Methods inherited from interface Collection

    equals, hashCode

  • Constructor Details

    • AbstractCollection

      protected AbstractCollection()
      Constructs a new instance of this AbstractCollection.

  • Method Details

    • add

      public boolean add(E object)
      Description copied from interface: Collection

      Attempts to add object to the contents of this Collection (optional).

      After this method finishes successfully it is guaranteed that the object is contained in the collection.

      If the collection was modified it returns true, false if no changes were made.

      An implementation of Collection may narrow the set of accepted objects, but it has to specify this in the documentation. If the object to be added does not meet this restriction, then an IllegalArgumentException is thrown.

      If a collection does not yet contain an object that is to be added and adding the object fails, this method must throw an appropriate unchecked Exception. Returning false is not permitted in this case because it would violate the postcondition that the element will be part of the collection after this method finishes.

      Parameters
      • object: the object to add.
      Returns
      Specified by:
      add in interface Collection<E>
      Returns:

      true if this Collection is modified, false otherwise.

      Throws

      • UnsupportedOperationException: if adding to this Collection is not supported.

      • ClassCastException: @throws ClassCastException if the class of the object is inappropriate for this collection.

      • IllegalArgumentException: if the object cannot be added to this Collection.

      • NullPointerException: if null elements cannot be added to the Collection.

    • addAll

      public boolean addAll(Collection<? extends E> collection)

      Attempts to add all of the objects contained in collection to the contents of this Collection (optional). This implementation iterates over the given Collection and calls add for each element. If any of these calls return true, then true is returned as result of this method call, false otherwise. If this Collection does not support adding elements, an UnsupportedOperationException is thrown.

      If the passed Collection is changed during the process of adding elements to this Collection, the behavior depends on the behavior of the passed Collection.

      Parameters
      • collection: the collection of objects.
      Returns
      Specified by:
      addAll in interface Collection<E>
      Returns:

      true if this Collection is modified, false otherwise.

      Throws

      • UnsupportedOperationException: if adding to this Collection is not supported.

      • ClassCastException: @throws ClassCastException if the class of an object is inappropriate for this Collection.

      • IllegalArgumentException: if an object cannot be added to this Collection.

      • NullPointerException: @throws NullPointerException if collection is null, or if it contains null elements and this Collection does not support such elements.

    • clear

      public void clear()

      Removes all elements from this Collection, leaving it empty (optional). This implementation iterates over this Collection and calls the remove method on each element. If the iterator does not support removal of elements, an UnsupportedOperationException is thrown.

      Concrete implementations usually can clear a Collection more efficiently and should therefore overwrite this method.

      Throws
      • UnsupportedOperationException: @throws UnsupportedOperationException it the iterator does not support removing elements from this Collection
      See also

      • #iterator

      • #isEmpty

      • #size

      Specified by:
      clear in interface Collection<E>

    • contains

      public boolean contains(Object object)

      Tests whether this Collection contains the specified object. This implementation iterates over this Collection and tests, whether any element is equal to the given object. If object != null then object.equals(e) is called for each element e returned by the iterator until the element is found. If object == null then each element e returned by the iterator is compared with the test e == null.

      Parameters
      • object: the object to search for.
      Returns

      true if object is an element of this Collection, false otherwise.

      Throws

      • ClassCastException: if the object to look for isn't of the correct type.

      • NullPointerException: @throws NullPointerException if the object to look for is null and this Collection doesn't support null elements.

      Specified by:
      contains in interface Collection<E>
      Returns:

      true if object is an element of this Collection, false otherwise.

      Throws

      • ClassCastException: @throws ClassCastException if the object to look for isn't of the correct type.

      • NullPointerException: @throws NullPointerException if the object to look for is null and this Collection doesn't support null elements.

    • containsAll

      public boolean containsAll(Collection<?> collection)

      Tests whether this Collection contains all objects contained in the specified Collection. This implementation iterates over the specified Collection. If one element returned by the iterator is not contained in this Collection, then false is returned; true otherwise.

      Parameters
      • collection: the collection of objects.
      Returns
      Specified by:
      containsAll in interface Collection<E>
      Returns:

      true if all objects in the specified Collection are elements of this Collection, false otherwise.

      Throws

      • ClassCastException: @throws ClassCastException if one or more elements of collection isn't of the correct type.

      • NullPointerException: @throws NullPointerException if collection contains at least one null element and this Collection doesn't support null elements.

      • NullPointerException: if collection is null.

    • isEmpty

      public boolean isEmpty()

      Returns if this Collection contains no elements. This implementation tests, whether size returns 0.

      Returns
      Specified by:
      isEmpty in interface Collection<E>
      Returns:

      true if this Collection has no elements, false otherwise.

      See also
      • #size

    • iterator

      public abstract Iterator<E> iterator()

      Returns an instance of Iterator that may be used to access the objects contained by this Collection. The order in which the elements are returned by the Iterator is not defined unless the instance of the Collection has a defined order. In that case, the elements are returned in that order.

      In this class this method is declared abstract and has to be implemented by concrete Collection implementations.

      Returns

      an iterator for accessing the Collection contents.

      Specified by:
      iterator in interface Collection<E>
      Specified by:
      iterator in interface Iterable<E>

    • remove

      public boolean remove(Object object)

      Removes one instance of the specified object from this Collection if one is contained (optional). This implementation iterates over this Collection and tests for each element e returned by the iterator, whether e is equal to the given object. If object != null then this test is performed using object.equals(e), otherwise using object == null. If an element equal to the given object is found, then the remove method is called on the iterator and true is returned, false otherwise. If the iterator does not support removing elements, an UnsupportedOperationException is thrown.

      Parameters
      • object: the object to remove.
      Returns
      Specified by:
      remove in interface Collection<E>
      Returns:

      true if this Collection is modified, false otherwise.

      Throws

      • UnsupportedOperationException: if removing from this Collection is not supported.

      • ClassCastException: if the object passed is not of the correct type.

      • NullPointerException: @throws NullPointerException if object is null and this Collection doesn't support null elements.

    • removeAll

      public boolean removeAll(Collection<?> collection)

      Removes all occurrences in this Collection of each object in the specified Collection (optional). After this method returns none of the elements in the passed Collection can be found in this Collection anymore.

      This implementation iterates over this Collection and tests for each element e returned by the iterator, whether it is contained in the specified Collection. If this test is positive, then the remove method is called on the iterator. If the iterator does not support removing elements, an UnsupportedOperationException is thrown.

      Parameters
      • collection: the collection of objects to remove.
      Returns
      Specified by:
      removeAll in interface Collection<E>
      Returns:

      true if this Collection is modified, false otherwise.

      Throws

      • UnsupportedOperationException: if removing from this Collection is not supported.

      • ClassCastException: @throws ClassCastException if one or more elements of collection isn't of the correct type.

      • NullPointerException: @throws NullPointerException if collection contains at least one null element and this Collection doesn't support null elements.

      • NullPointerException: if collection is null.

    • retainAll

      public boolean retainAll(Collection<?> collection)

      Removes all objects from this Collection that are not also found in the Collection passed (optional). After this method returns this Collection will only contain elements that also can be found in the Collection passed to this method.

      This implementation iterates over this Collection and tests for each element e returned by the iterator, whether it is contained in the specified Collection. If this test is negative, then the remove method is called on the iterator. If the iterator does not support removing elements, an UnsupportedOperationException is thrown.

      Parameters
      • collection: the collection of objects to retain.
      Returns
      Specified by:
      retainAll in interface Collection<E>
      Returns:

      true if this Collection is modified, false otherwise.

      Throws

      • UnsupportedOperationException: if removing from this Collection is not supported.

      • ClassCastException: @throws ClassCastException if one or more elements of collection isn't of the correct type.

      • NullPointerException: @throws NullPointerException if collection contains at least one null element and this Collection doesn't support null elements.

      • NullPointerException: if collection is null.

    • size

      public abstract int size()

      Returns a count of how many objects this Collection contains.

      In this class this method is declared abstract and has to be implemented by concrete Collection implementations.

      Returns
      Specified by:
      size in interface Collection<E>
      Returns:
      how many objects this Collection contains, or Integer.MAX_VALUE if there are more than Integer.MAX_VALUE elements in this Collection.

    • toString

      public String toString()

      Returns the string representation of this Collection. The presentation has a specific format. It is enclosed by square brackets ("[]"). Elements are separated by ', ' (comma and space).

      Returns

      the string representation of this Collection.

      Overrides:
      toString in class Object

    • toArray

      public Object[] toArray()

      Returns a new array containing all elements contained in this ArrayList.

      Returns

      an array of the elements from this ArrayList

      Specified by:
      toArray in interface Collection<E>

    • toArray

      public <T> T[] toArray(T[] contents)

      Returns an array containing all elements contained in this ArrayList. If the specified array is large enough to hold the elements, the specified array is used, otherwise an array of the same type is created. If the specified array is used and is larger than this ArrayList, the array element following the collection elements is set to null.

      Parameters
      • contents: the array.
      Returns

      an array of the elements from this ArrayList.

      Throws
      • ArrayStoreException: @throws ArrayStoreException when the type of an element in this ArrayList cannot be stored in the type of the specified array.
      Specified by:
      toArray in interface Collection<E>