Java Collection Interface

The Collection interface is the root interface of the Java collections framework.

There is no direct implementation of this interface. However, it is implemented through its subinterfaces like List, Set, and Queue.

For example, the ArrayList class implements the List interface which is a subinterface of the Collection Interface.

Java Collection Interface and its subinterfaces.

Subinterfaces of Collection

As mentioned above, the Collection interface includes subinterfaces that are implemented by various classes in Java.

1. List Interface

The List interface is an ordered collection that allows us to add and remove elements like an array. To learn more, visit: Java List Interface.

2. Set Interface

The Set interface allows us to store elements in different sets similar to the set in mathematics. It cannot have duplicate elements. To learn more, visit: Java Set Interface.

3. Queue Interface

The Queue interface is used when we want to store and access elements in First In, First Out(FIFO) manner. To learn more, visit: Java Queue Interface.

Methods of Collection

The Collection interface includes various methods that can be used to perform different operations on objects. These methods are available in all its subinterfaces.

  • add() - inserts the specified element to the collection
  • size() - returns the size of the collection
  • remove() - removes the specified element from the collection
  • iterator() - returns an iterator to access elements of the collection
  • addAll() - adds all the elements of a specified collection to the collection
  • removeAll() - removes all the elements of the specified collection from the collection
  • clear() - removes all the elements of the collection

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