ArrayList<Integer> al=new ArrayList<Integer>();Initially memory is allocated for elements later that can be growable to any number of elements
Syntax: al.add(element);Which can be used to add the an element at the endof arraylist.
syntax: al2.addAll(al1);Elements of al1 objects will be added to al2 object.
ArrayList<Integer> al2; al2=(ArrayList)al.clone();Duplicate object is created for 'al1' for whose reference is assigned to al2.
al.remove(indexvalue);It can be removed not only based on index value but also it is possible throw element or value.