Collection Interface

Collection Interface is the Root interface in the collection hierarchy.

 

Important properties Collection interface

  1. JDK does not provide any direct implementations of this interface: it provides implementations of more specific subinterfaces like Set and List etc.

  2. All child classes (direct or indirect) should provide minimum two constructors: a no argument constructor, which creates an empty collection, and a constructor with a single argument of type Collection, which creates a new collection with the same elements as its argument.

  3. Overriden methods should throw UnsupportedOperationException if this collection does not support the operation.  

    • may, but are not required to, throw an UnsupportedOperationException if the invocation would have no effect on the collection.

      • For example, invoking the addAll(Collection) method on an unmodifiable collection may, but is not required to, throw the exception if the collection to be added is empty.

 

Method Summary

  • add(E e)

    • Add element e

  • addAll(Collection<? extends E> c)

    • Add all from specified collection

  • clear()

    • clear collection

  • contains(Object o)

    • if o is present

  • containsAll(Collection<?> c)

    • if this collection contains all of the elements in the specified collection.

  • equals(Object o)

    • Check if meaningfully equal

  • hashCode()

    • Return hash code integer

  • isEmpty()

    • Check if empty

  • iterator()

    • Return an iterator

  • remove(Object o)

    • Remove o

  • removeAll(Collection<?> c)

    • Remove all elements present in the specified collection

  • retainAll(Collection<?> c)

    • Retains only the elements in this collection that are contained in the specified collection

  • size()

    • size of the collection

  • toArray()

    • convert to an array

  • toArray(T[] a)

    • runtime type of the returned array is that of the specified array.

 

Following methods from the above list are marked as optional

  • add(E e)

  • addAll(Collection<? extends E> c)

  • clear()

  • remove(Object o)

  • removeAll(Collection<?> c)

  • retainAll(Collection<?> c)

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