java maximum value of int

Question

From java documentation int has a minimum value of -2,147,483,648 and a maximum value of 2,147,483,647 (inclusive).

I have a class Test.java.

public class Test
{
    public static void main(String[] args)
    {
        int i=2147483647; //max positive value an int can store
        for(;;)
        {
            System.out.println(++i);
        }
    }
}

As per my knowledge ++i should increment the value of i by 1 and throw exception, because 2147483648 is not allowed in int.

But when I run above program it goes running(because of infinite loop), and instead of incrementing the value to 2147483648, the value assigned to i is -2147483648, And values is decremented each time by 1.

Sample run (after modifying class)

public static void main(String[] args)
{
    int i=2147483647;
    for(;;)
    {
        System.out.println(++i);
        System.out.println(++i);
        System.out.println(++i);
        System.out.println(++i);
        System.out.println(++i);
        break;
    }
}

Output:

-2147483648
-2147483647
-2147483646
-2147483645
-2147483644

Answers/Hints will be appreciated.

score 13 · Accepted Answer · answered Sep 28 '13 at 11:18

As per my knowledge ++i should increment the value of i by 1 and throw exception, because 2147483648 is not allowed in int.

Your understanding is incorrect. Integer arithmetic overflows silently in Java.

From section 15.18.2 of the JLS:

If an integer addition overflows, then the result is the low-order bits of the mathematical sum as represented in some sufficiently large two's-complement format. If overflow occurs, then the sign of the result is not the same as the sign of the mathematical sum of the two operand values.

score 4 · Answer 2 · answered Sep 28 '13 at 11:18

4

You've encountered a situation known as integer overflow: http://en.wikipedia.org/wiki/Integer_overflow

answered Sep 28 '13 at 11:18

Mureinik

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score 2 · Answer 3 · answered Sep 28 '13 at 11:19

2

This is known as integer overflow. Arithmetic operations on integer values never throw an exception, and this is not a Java-only thing.

The minimum and maximum values only serves you to decide if an int is or is not enough for your computation.

answered Sep 28 '13 at 11:19

Raffaele

20,627
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score 2 · Answer 4 · answered Sep 28 '13 at 11:19

2

I won't give the exact answer, but consider this:

how is an integer represented in Java(in what kind of binair number representation)?
what happens if you add 1 to the highest possible binair number?

answered Sep 28 '13 at 11:19

Tom

133
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Alpesh Gediya · Answer 5 · 2013-09-28T11:27:15.670

2

In java underflow and overflow of numeric values are off(silent). During underflow and overflow event Java keeps continuing incrementing/decrementing for numeric value's range.

Section 4.2.2. Integer Operations

The integer operators do not indicate overflow or underflow in any way.

edited Sep 28 '13 at 11:27

answered Sep 28 '13 at 11:20

Alpesh Gediya

3,706
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java maximum value of int

5 Answers5

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