Map.clear() vs new Map : Which one will be better? [duplicate]

Complicated question. Let's see what happens.

You instantiate a new instance, which is backed with new array. So, garbage collector should clear all the key and values from the previous map, and clear the reference to itself. So O(n) algorithm is executed anyway, but in the garbage collector thread. For 1000 records you won't see any difference. BUT. The performance guide tells you that it is always better not to create new objects, if you can. So I would go with clear() method.

Anyway, try both variants and try to measure. Always measure!

When you say Map.clear() on a Map of size n... You are asking the GC to clean up 2*n (Key & Value) objects. When you say null to the same Map, you are asking the GC to clean up 2*n+1 (1 for the Map itself) objects. Then you will have to create a new Map instance yet another overhead. So go for Map.clear(). You will be wise to preset the size of the Map while instantiating it.

I thought Creating object in java more expensive in terms of memory,so it is better to you go with .clear(),so you are using same object instead of creating new one