What is difference between Long object and primitive type long in Java?

Question

I thought long and Long class are more or less same thing. I saw this link

When I displayed Long.MAX_VALUE it displayed 9223372036854775807. But when I was doing multiplication of 1000000*1000000 which is 10^12 ; it gave overflow.

I was using long data type to store value...and while debugging it had value -727379968 after multiplication

Where am I making mistake or I am totally dumb?

Update: This was my code, and I got my mistake as specified in answer.

 
 for (;;)
    ppltn[i] = Integer.parseInt(tk.nextToken());

 for (int i = 0; i < noc; i++)  //sum is of long type
    sum = sum + min * ppltn[i];  //min and ppltn are of integer type

I know it would if value is greater than "9223372036854775807" but not for 10^12 — Sumit Murari, Mar 01 '14 at 06:26
I don't know where, but I'm making some silly-silly silly mistake ... — Sumit Murari, Mar 01 '14 at 06:28

score 4 · Accepted Answer · answered Mar 01 '14 at 06:35

The expression

1000000 * 1000000;

is integer multiplication as both operands are integers. Therefore you are limited by the max value of an integer.

You need to do long multiplication

1000000L * 1000000 /* L if you want it*/;

where at least one operand is a long and the other gets promoted to a long (if it isn't already).

Adrian Shum · Answer 2 · 2014-03-01T06:42:25.850

2

In Java, ^ doesn't mean "power". It is a bitwise XOR operator.

therefore 10^6 means 10 XOR 6 instead 10 * 10 * 10 * 10 * 10 * 10

it is hard to guess without seeing your code.

However my guess is you are doing somehting like

long l = 1000000 * 10000000;

If so, here is the problem.

literal 1000000 is in fact an int instead of long, and therefore, 1000000 * 10000000 is doing a int multiplication and it got overflow (max of int is something around 2,xxx,xxx,xxx). The "overflowed" value is then cast to a long. Which give you the "strange" result.

edited Mar 01 '14 at 06:42

answered Mar 01 '14 at 06:28

Adrian Shum

38,812
10
83
131

Where's the overflow in that? – Sotirios Delimanolis Mar 01 '14 at 06:29
@SotiriosDelimanolis what do you mean? there is nothing as "overflow" for XOR – Adrian Shum Mar 01 '14 at 06:30
I want your answer to explain `But when I was doing multiplication of 10^6*10^6 which is 10^12 and it gave overflow.` – Sotirios Delimanolis Mar 01 '14 at 06:31
I'm sorry it's 1000000*1000000 – Sumit Murari Mar 01 '14 at 06:32
I think you should be clear on the question. It do make me think that you are having `10^6` as the expression. See my update then – Adrian Shum Mar 01 '14 at 06:33
While I agree with the overflow synopsis, 8,xxx,xxx (~8 million) is not even close for an integer limit! 2^32 is ~4 billion, 2^31-1 (the maximum int value) is ~2 billion. – user2864740 Mar 01 '14 at 06:38
stupid me, some problem when hitting the calculator lol. Yes, 2,xxx,xxx,xxx is the max of `int`. It IS already an overflow for your 1,000,000 * 1,000,000 result anyway. – Adrian Shum Mar 01 '14 at 06:41

What is difference between Long object and primitive type long in Java?

2 Answers2