CareerCup

A link List implementation would be more efficient.
Something like

public class Node {
	Object key;
	Node next;
	ValueNode vnode;
}
public class ValueNode {
	Object Value;
	ValueNode next;
}

You can implement a multi-map with a balanced binary search tree (AVL tree), which is very easy to implement. Each key can have many values and you cannot use any of the java collections. That's why I would suggest you to use a linked list (implemented by you) as a value.

what I could think of :
-Define a 2d array.
-1st index of each array will be the key ant the rest will be the value of the multimap.
-on addition of a element create a copy the whole and add new element in the last index.

this requires a lot of copying of arrays.

-Define a 2d array.
-1st index of each array will be the key ant the rest will be the value of the multimap.
-on addition of a element check if space avalabel for new recoer then add new element in the last index else create new 2d arrey of double size than exising arrey and copy existing value then add new.