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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.


  • 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.

arraylist java

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

arraylist java collection

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();
		System.out.println(l);//      [A,10,A,null]
		System.out.println(l);//      [A,10,null]
		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).

arraylist java collection example



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.

ArrayList l1 = new ArrayList();
List l = Collections.SynchronizedList(l1);

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

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