Java performance tips – Part 1 : Vector, ArrayList & LinkedList

When, where & how to use Vector & ArrayList

Even though both Vector & ArrayList are used for the same purpose – as a dynamic collection of related objects – there is a right time and place to use them. As we all know there is a major difference: Vector is thread-safe but ArrayList is not. If there is no need of synchronization we can use ArrayList instead of Vector. And that will definitely be a performance booster.

When size matters

Internally both Vector & ArrayList uses arrays to hold the elements. Both supports an initialCapacity parameter which decides the initial size of the array. (I really don’t remember the default value). Once if the capacity becomes insufficient to accommodate new elements either of these collections need to expand their capacity. Both Vector & ArrayList do it differently. Vector doubles the current capacity & ArrayList increases the capacity by 50%. Whenever we create a Vector we can specify a capacityIncrement parameter; which is an integer using which the capacity will get incremented whenever the Vector overflows.

Its also advised that, if we know the maximum number of elements that gonna be inserted in to the collection, we should set it as the initialCapacity while creating the collection itself. But its not practically possible every time.

Element access & performance

In both Vector & ArrayList addition/deletion of elements at one end & accessing the elements at a particular index wont take much effort (just O(1) ). But adding or deleting an element at the i-th position will take some effort based on the value of i (O(n-i), where n is the size of the collection). Use of a LinkedList can help us here. B’ coz in a LinkedList addition/deletion of elements is pretty easy as it’s a matter of adjusting the pointers (just O(1)).

LinkedList is good, but…

The problem with LinkedList is that it will create an object for each element being added to the list. Means double the duty for the garbage collector. And as LinkedList is not using arrays to hold elements, it’s a bit painful for it to access elements at a particular index (O(i), where i the index).

So, programmers should decide when to use what based on the requirement.