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AbstractCollection


java.util

Class AbstractCollection<E>

  • All Implemented Interfaces:
    Iterable<E>, Collection<E>
    Direct Known Subclasses:
    AbstractList, AbstractQueue, AbstractSet, ArrayDeque, ConcurrentLinkedDeque


    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 and Description
      protected AbstractCollection()
      Constructs a new instance of this AbstractCollection.
    • Method Summary

      Methods
      Modifier and Type Method and 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 Collection.
      <T> T[] toArray(T[] contents)
      Returns an array containing all elements contained in this Collection.
      String toString()
      Returns the string representation of this Collection.
    • Constructor Detail

      • AbstractCollection

        protected AbstractCollection()
        Constructs a new instance of this AbstractCollection.
    • Method Detail

      • 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.
        Specified by:
        add in interface Collection<E>
        Parameters:
        object - the object to add.
        Returns:
        true if this Collection is modified, false otherwise.
      • 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.

        Specified by:
        addAll in interface Collection<E>
        Parameters:
        collection - the collection of objects.
        Returns:
        true if this Collection is modified, false otherwise.
        Throws:
        UnsupportedOperationException - if adding to this Collection is not supported.
        ClassCastException - if the class of an object is inappropriate for this Collection.
        IllegalArgumentException - if an object cannot be added to this Collection.
        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.

        Specified by:
        clear in interface Collection<E>
        Throws:
        UnsupportedOperationException - it the iterator does not support removing elements from this Collection
        See Also:
        iterator(), isEmpty(), size()
      • 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.
        Specified by:
        contains in interface Collection<E>
        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 - 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.
        Specified by:
        containsAll in interface Collection<E>
        Parameters:
        collection - the collection of objects.
        Returns:
        true if all objects in the specified Collection are elements of this Collection, false otherwise.
        Throws:
        ClassCastException - if one or more elements of collection isn't of the correct type.
        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.
        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.

        Specified by:
        iterator in interface Iterable<E>
        Specified by:
        iterator in interface Collection<E>
        Returns:
        an iterator for accessing the Collection contents.
      • 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.
        Specified by:
        remove in interface Collection<E>
        Parameters:
        object - the object to remove.
        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 - 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.

        Specified by:
        removeAll in interface Collection<E>
        Parameters:
        collection - the collection of objects to remove.
        Returns:
        true if this Collection is modified, false otherwise.
        Throws:
        UnsupportedOperationException - if removing from this Collection is not supported.
        ClassCastException - if one or more elements of collection isn't of the correct type.
        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.

        Specified by:
        retainAll in interface Collection<E>
        Parameters:
        collection - the collection of objects to retain.
        Returns:
        true if this Collection is modified, false otherwise.
        Throws:
        UnsupportedOperationException - if removing from this Collection is not supported.
        ClassCastException - if one or more elements of collection isn't of the correct type.
        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.

        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.
      • toArray

        public Object[] toArray()
        Description copied from interface: Collection
        Returns a new array containing all elements contained in this Collection. If the implementation has ordered elements it will return the element array in the same order as an iterator would return them. The array returned does not reflect any changes of the Collection. A new array is created even if the underlying data structure is already an array.
        Specified by:
        toArray in interface Collection<E>
        Returns:
        an array of the elements from this Collection.
      • toArray

        public <T> T[] toArray(T[] contents)
        Description copied from interface: Collection
        Returns an array containing all elements contained in this Collection. 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 Collection, the array element following the Collection elements is set to null. If the implementation has ordered elements it will return the element array in the same order as an iterator would return them. toArray(new Object[0]) behaves exactly the same way as toArray() does.
        Specified by:
        toArray in interface Collection<E>
        Parameters:
        contents - the array.
        Returns:
        an array of the elements from 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).
        Overrides:
        toString in class Object
        Returns:
        the string representation of this Collection.


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