Java List Interface

Java List Interface

• List Interface is the of Collection. 
• The Java.util.List is a child interface/subinterface of Collection. 
• It is a factory of ListIterator interface.
• It contains index-based methods to insert and delete elements. 
• Elements can be inserted or accessed by their position in the list, using a zero-based index.
• A list may contain duplicate elements.
• List Interface is implemented by the classes of ArrayList, LinkedList, Vector and Stack.

Syntax:
public interface List extends Collection

• How to create List Objects:
• Objects can be non-generic and generic.

Generic Vs Non-Generic object:

• Java collection framework was non-generic before JDK 1.5, since 1.5, it is generic.
• Java's new generic collection allows you to have only one type of object in the collection. So, it is type-safe for typecasting dows not required at run time.
• Example of old non-generic java collection.
• Example:
              List AL = new ArrayList();               List LL = new LinkedList();               List V = new Vector();               List S = new Stack();
• Example of new non-generic java collection.
• Example:
              List <string> al = new ArrayList<string>();

• In generic collection, we need to specify the type in angular braces.
• After the introduction of Generics in Java 1.5, it is possible to restrict the type of object that can be stored in the List. 
• Example: List&ltObj&gt list = new ArrayList&ltObj&gt ();
• Note: Obj is the type of object to be stored in List

Methods:

• How to add a given element at a specified index?
• void add(int index, Object O): This method adds a given element at a specified index.
• Example: 

                         List l1 = new ArrayList();
                                          l1.add(0, 1);
                                         l1.add(1, 2);

• How to print all elements?
• Example:  System.out.println(l1);

• How to add collection in to list?
• boolean addAll(int index, Collection c): This method adds all elements from specified collection to list. 
• Example:

                  List l2 = new ArrayList();
                                                 l2.add(1);
                                                 l2.add(2);
                                                 l2.add(3);
                  l1.addAll(1, l2);

• How to remove a specific item at position?
• Object remove(int index): This method removes an element from the specified index.
• Example: l1.remove(1);

• How to get specific item at position?
• Object get(int index): This method returns an element at the specified index.
• Example:  System.out.println(l1.get(3)); 

• How to change specific item at the position?
• Object set(int index, Object new): This method replaces the element at a given index with a new element. 
• Example: l1.set(0, 5);

• How to search the first occurrence of the given element?
• int indexOf(Object o): This method returns the first occurrence of a given element or -1 if an element is not present in the list.
• Example: System.out.println("first index of 2:"+ l1.indexOf(2)); 

• How to search the last occurrence of the given element?
• int lastIndexOf(Object o): This method returns the last occurrence of a given element or -1 if an element is not present in the list.
• Example: System.out.println("last index of 2:"+ l1.lastIndexOf(2));

• How to get a portion of the given List between two indices?

• List subList(int fromIndex, int toIndex):This method returns List view of specified List between fromIndex(inclusive) and toIndex(exclusive).
• Example:

List range = new ArrayList();
                          // Return List from 2nd(including) and 4th element(excluding)
                          range = l1.subList(2, 4);
System.out.println("Sublist : "+ range);

• How to clear all elements from list?
• void clear(): It is used to remove all of the elements from this list.
• Example:

l1.clear();

• How to display all elements using for each loop?
• Example:

for(Integer s:l1){
                                             System.out.println(s);
}

• Write all method of Java ListIterator Interface?
• void add(E e): This method inserts the specified element into the list.
• boolean hasNext(): This method returns true if the list iterator has more elements while traversing the list in the forward direction.
• E next(): This method returns the next element in the list and advances the cursor position.
• int nextIndex(): This method returns the index of the element that would be returned by a subsequent call to next()
• boolean hasPrevious(): This method returns true if this list iterator has more elements while traversing the list in the reverse direction.
• E previous(): This method returns the previous element in the list and moves the cursor position backward.
• E previousIndex(): This method returns the index of the element that would be returned by a subsequent call to previous().
• void remove(): This method removes the last element from the list that was returned by next() or previous() methods
• void set(E e): This method replaces the last element returned by next() or previous() methods with the specified element.

• How to traversing elements in forward direction using ListIterator?
• Example:

ListIterator itr=l1.listIterator(); 
                       System.out.println("Traversing elements in forward direction"); 
                       while(itr.hasNext()){ 
System.out.println("index:"+itr.nextIndex()+" value:"+itr.next());
                       } 

• How to traversing elements in backward direction using ListIterator?
• Example:

ListIterator itr=l1.listIterator(); 
System.out.println("Traversing elements in backward direction"); 
                      while(itr.hasPrevious()){   
                      System.out.println("index:"+itr.previousIndex()+"value:"+itr.previous());
                      }