• Collection is the main interface.
• There are many methods declared in Collection interface. These are the common methods for all collections to perform different operations.

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.