JAVA LIST INTERFACE

Some of the important points about Java List are:

·       List Interface is the sub interface of Collection.

·       It contains index-based methods to insert and delete elements.

·       It is an ordered collection of objects in which duplicate values can be stored.

·       Since List preserves the insertion order, it allows positional access and insertion of elements.

·       List Interface is implemented by ArrayList, LinkedList, Vector and Stack classes.

·       List allows you to add duplicate elements.

·       List allows you to have ‘null’ elements.

·       List indexes start from 0, just like arrays.

1. List Interface declaration

·       public interface List<E> extends Collection<E>  

2. Java List Example

1.   import java.util.*;  

2.   public class ListExample{  

3.   public static void main(String args[]){  

4.   List<String> al=new ArrayList<String>();  

5.   al.add("Amit");  

6.   al.add("Vijay");  

7.   al.add("Kumar");  

8.   al.add(1,"Sachin");  

9.   System.out.println("An element at 2nd position: "+al.get(2));  

10.     for(String s:al){  

11.     System.out.println(s);  

12.     }  

13.     }  

14.     }  

Output:

  An element at 2nd position: Vijay
Amit
Sachin
Vijay
Kuma

Java List Methods

Some of the useful Java List methods are;

1.     int size(): to get the number of elements in the list.

2.     boolean isEmpty(): to check if list is empty or not.

3.     boolean contains(Object o): Returns true if this list contains the specified element.

4.     Iterator<E> iterator(): Returns an iterator over the elements in this list in proper sequence.

5.     Object[] toArray(): Returns an array containing all of the elements in this list in proper sequence

6.     boolean add(E e): Appends the specified element to the end of this list.

7.     boolean remove(Object o): Removes the first occurrence of the specified element from this list.

8.     boolean retainAll(Collection<?> c): Retains only the elements in this list that are contained in the specified collection.

9.     void clear(): Removes all the elements from the list.

10. E get(int index): Returns the element at the specified position in the list.

11. E set(int index, E element): Replaces the element at the specified position in the list with the specified element.

12. ListIterator<E> listIterator(): Returns a list iterator over the elements in the list.

13. List<E> subList(int fromIndex, int toIndex): Returns a view of the portion of this list between the specified fromIndex, inclusive, and toIndex, exclusive. The returned list is backed by this list, so non-structural changes in the returned list are reflected in this list, and vice-versa.

Some of the default methods added to List in Java 8 are;

1. default void replaceAll(UnaryOperator<E> operator): Replaces each element of this list with the result of applying the operator to that element.

2. default void sort(Comparator<super E> c): Sorts this list according to the order induced by the specified Comparator.

3. default Spliterator<E> spliterator(): Creates a Spliterator over the elements in this list.