Collection interface in java

The Collection Interface in Java is the root interface(a kind of abstract class) in java.util package. It represents a group of objects, known as elements, and provides a unified way to manipulate and work with collections of data.

Key Points About the Collection Interface

Root Interface: The Collection interface is the root interface of all Collection objects in Java, except Map.

Generic Interface: A generic interface, meaning it can work with any type of object (_e.g.,_ Collection<String>, Collection etc.).

Common Methods: For example, we can use the following methods for both adding and deleting elements to an array: add(), remove (), size().

Extends Iterable: The Collectioneuml; interface extends the Iterableinterface, and this means that all collections can be iterated over via either an iterator or the enhanced for-loop construct.

1. public interface Collection<E>
2. extends Iterable<E>

Methods in Collection Interface:

 1.public Boolean add(Object obj)

•  Used to add element in to the collection

 2.public Boolean addAll(Collection c)

• Adds all the elements of c to the invoking collection. Returns true if the operation succeeded else returns false.

 3.public boolean isEmpty()

• Returns true if collection is empty otherwise returns false.

 4.public boolean remove(Object obj)

• Remove element from collection. Returns true if successful deletion.

5.public boolean  removeAll(Collection c)

• Removes all elements of a collection.

 6.public void clear()

• Deletes total elements from collection

 7.public boolean contains(Object obj)

• This method used to search an element

 8.public boolean containsAll(Collection c)

• This method used to search an element in a collection

 9.public boolean retianAll(Collection c)

• Used to delete all elements from a collection except specified one.

10.public int size()

• Returns total numbers of elements in a collection

11.public Iterator iterator()

• Returns iterator for the collection

12.public boolean equals(Object obj)

• Compares two collections

13.public int hashCode()

• Returns hashcode

14.public Object[] toArray()

• This method used to convert collection into array

15.public Object[] toArray(Object[] obj)

• Returns an array containing only those collection elements whose type matches that of array.

Difference Between Collection and Collections:

• Collection is the base interface for most of the classes.
• Collections is the utility class.