Java ArrayList class

ArrayList class :

•  Resizable Array or growable array.
•  The underlined datastructure resizable and growable array.
•  Duplicates are allowed.
•  Insertion order is preserved.
•  Heterogeneous objects are allowed(Except Tree Set and Tree Map everywhere heterogeneous objects are allowed).
•  Null insertion is possible.

CONSTRUCTOR:

• ArrayList l = new ArrayList():- Creates an empty ArrayList object with default initial capacity 10.Once ArrayList reaches its max capacity a new ArrayList will be created.

• After copying all the data into another arraylist garbage collector will de-allocate the first arraylist memory.

New Capacity = [ Current Capacity * 3/2 ] + 1

• ArrayList l = new ArrayList(int initialCapacity);
• ArrayList l = new ArrayList(Collection c);

Example for Arraylist:

Import java.util.*;
Class ArrayListDemo{
	public static void main(String[] args)
	{
		ArrayList l = new ArrayList();
		L.add(“A”);
		l.add(10);
		l.add(“A”);
		l.add(null);
		System.out.println(l);//      [A,10,A,null]
		l.remove(2);
		System.out.println(l);//      [A,10,null]
		l.add(“2”,”m”);
		l.add(“n”); 
		System.out.println(l); //      [A,10,m,null,n]
	}
}

Note : We will get the output in brackets. Because object reference internally its going to implemented as toString method.

When Arraylist is best and worst choice?

• Arraylist is the best choice if our requirement is retrieval operation(Because Arraylist implements RandomAccess interface).
• ArrayList is the worst choice if our requirement is insertion or deletion in the middle(Because shift operation are required).

l.add(1,”m”);

l.remove(1);

How to get Synchronized version of ArrayList object?

By default ArrayList is object is non-synchronized but we can get synchronized version of ArrayList by using collection class SynchronizedList() method.

NON-SYNCHRONIZED:
ArrayList l1 = new ArrayList();
SYNCHRONIZED:
List l = Collections.SynchronizedList(l1);

Point : Similarly we can get synchronized version of Set, Map objects by using the following methods of collection class