Java Collections Framework

Java Collections Framework

• java.utils에 속한 일련의 클래스로, 자료구조를 담당
• 잘 짜여진 interface를 기반으로 다양한 자료구조를 구현
• Generic class로 되어 있어, 다양한 객체를 요소로 담을 수 있다.

some are excerpted from Java collections overview

Advantages of a collections framework

• Reduces programming effort
• Increase performance
• Provide interoperability between unrelated APIs
• Reduces the effort required to learn APIs
• Reduces the effort required to design and implement APIs
• Fosters software reuse

Collection Interfaces

• Collection
  • A group of objects. No assumptions are made about the order of the collection (if any) or whether it can contain duplicate elements.
• Set
  • The familiar set abstraction. No duplicate elements permitted. May or may not be ordered. Extends the Collection interface.
• List
  • Ordered collection, also known as a sequence. Duplicates are generally permitted. Allows positional access. Extends the Collection interface.
• Queue
  • A collection designed for holding elements before processing. Besides basic Collection operations, queues provide additional insertion, extraction, and inspection operations.
• Deque
  • A double ended queue, supporting element insertion and removal at both ends. Extends the Queue interface.
• Map
  • A mapping from keys to values. Each key can map to one value.

Method of Collection Interfaces

Method	Description
boolean add(E e)	Ensures that collection contains the specified element.
boolean addAll(Collection<? exteionds E> c)	Adds all of the elements in the specified collection to this collection.
void clear()	Removes all of the elements from this collection.
boolean contains(Object o)	Returns true if this collection contains the specified element.
boolean containsAll(Collection<?> c)	Returns true if this collection contains all of the elements in the specified collection.
boolean equals(Object o)	Compares the specified object with this collection for equality.
boolean isEmpty()	Returns true if this collection contains no elements.
Iterator<E> iterator()	Returns true if this collection contains on elements.
boolean remove(Object o)	Remove a single instance of the specified elemtns from this collection, if it is present.
boolean removeAll(Collection<?> c)	Removes all of this collection’s elements that are also contained in the specified collection.
boolean retainAll(Collection<?> c)	Retains only the elements in this collection that are contained in the specified collection.
int size()	Returns the number of elements in this collection.
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.