Why Does My Java Code Fail with an Integer Overflow When Trying to Find Prime Factors of 600851475143?

Integer Overflow with Large Numbers

The code snippet above attempts to find the largest prime factor of a given integer, 600851475143. However, when the code is run, it fails with an error message indicating that the integer is too large.

When working with large numbers in Java, it's important to be mindful of the available data types and their limits.

Integers

Integers in Java are represented using fixed-width values. 32-bit integers (type int) can hold values from -2^31 to 2^31-1 (approximately -2 billion to 2 billion). 64-bit integers (type long) can hold values from -2^63 to 2^63-1 (approximately -9 quintillion to 9 quintillion).

In the example code, the given number, 600851475143, exceeds the range of 32-bit integers. As a result, Java interprets the literal value as a 32-bit integer and incorrectly truncates it to a negative value, leading to the overflow error.

Long Literals

To specify a literal value as a 64-bit integer, it must be suffixed with "L". For example, 600851475143L is a valid representation of the desired number in Java.

Revised Code

By changing the literal value to 600851475143L, we can fix the overflow issue and successfully execute the program.

...
        obj.function(600851475143L);
...

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