What is the memoy size of a Java object array after it has been created?

Question

This probably doesn\'t even need asking, but I want to make sure I\'m right on this. When you create an array of any object in Java like so:

Object[] objArr         


        

Answer 1

The null references do "take up space" -- the array's memory is allocated up-front in one chunk, and zeroed (to make all of the contents null references). As an exercise, try allocating a huge array, one that will take up more space than your JVM's memory limit. The program should immediately terminate with an out of memory error.

Answer 2

I think this will be helpful to you

public static void main(String[] args) {
        Runtime r = Runtime.getRuntime();
        System.gc();
        System.out.println("Before " + r.freeMemory());
        Object[] objArr = new Object[10];
        System.out.println("After " + r.freeMemory());
        objArr[0] = new Integer(3);
        System.gc();
        System.out.println("After Integer Assigned " + r.freeMemory());
    }

Output

Before 15996360
After 15996360
After Integer Assigned 16087144