CODEWITHSUNDEEP
javamemory
user1866509
user1866509

Reputation: 3

Memory usage by Array of Long, Array of Integer and ArrayList

Whether I use Long[], Integer[] or ArrayList<Integer>, why do all of them return the same memory usage?

System.out.println("Memory Usage : " + Runtime.getRuntime().totalMemory()/(1024*1024));
System.out.println("Memory Usage : " + (Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory())/(1024*1024));

//Long[] aa = new Long[70000000];
Integer[] bb = new Integer[70000000];
//ArrayList<Integer> a = new ArrayList<Integer>(70000000);

System.gc();

System.out.println("Memory Usage : " + Runtime.getRuntime().totalMemory()/(1024*1024));
System.out.println("Memory Usage : " + (Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory())/(1024*1024));

Upvotes: 0

Views: 326

Answers (1)

Jon Skeet
Jon Skeet

Reputation: 1499770

In the above statements Whether i use Long[], Integer[] or ArrayList, why all of them give same memory usage ?

It makes perfect sense. In all cases, you're basically allocating an array which is 70000000 * (size of reference on your JVM). The size of an Integer reference is the same as the size of a Long reference, which is the same as the size of an Object reference. In the ArrayList case you've got the very small additional overhead of the ArrayList object itself, but that's pretty small - and easily explained as per Louis's comment.

If you actually populated those arrays, creating instances of Long and Integer, then you'd see a difference. Likewise if you created a long[] vs an int[], you'd see a difference.

Upvotes: 6

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