CODEWITHSUNDEEP
javaprimitive-types
shanlodh
shanlodh

Reputation: 1045

Java: Casting double to int > Integer.MAX_VALUE

I'm trying to do the following problem from "Core Java for the Impatient" -

"What happens when you cast a double to an int that is larger than the largest possible int value?"

Code:

package ch01.sec01;
import java.util.Random;

public class Exercise_5{
    public static void main(String[] args){
        int max = 10000;
        int min = 1000; 
        Random rand = new Random(); 
        double randomDouble = Integer.MAX_VALUE + rand.nextInt((max - min) + 1);
        System.out.println("randomDouble: " +randomDouble);
        int intFromDouble = (int)randomDouble;
        System.out.println("intFromDouble: " +intFromDouble); 
    }
}

Output: 

randomDouble: -2.147475257E9
intFromDouble: -2147475257

I'm wondering why randomDouble takes a negative value since primitve double has a wider range than primitive int and so there should be no overflow issues and what would be the correct way to get a double greater than Integer.MAX_VALUE?

Thanks

Upvotes: 1

Views: 1559

Answers (3)

azro
azro

Reputation: 54168

Your line does not cast the 2 part as double, and then sum them, but it sum them which results in an overflow, and them you just put in a double

double randomDouble = Integer.MAX_VALUE + rand.nextInt((max - min) + 1);

Upvotes: 1

Tim Biegeleisen
Tim Biegeleisen

Reputation: 522109

In the expression:

double randomDouble = Integer.MAX_VALUE + rand.nextInt((max - min) + 1);

the right hand side of the expression will first assign the sum to an integer, then this result will be cast to a double. Since adding anything to Integer.MAX_VALUE will result in overflow, you end up with a negative number, because the sign bit gets flipped as part of the overflow.

If you want a double, then just cast MAX_VALUE to double:

double randomDouble = (double)Integer.MAX_VALUE + (double)rand.nextInt((max - min) + 1);

Now in this case you get what you want, because you are adding a random number to a double, which is bearing the largest int value, which is not near the limit for what doubles can store.

Demo

Upvotes: 3

Viç
Viç

Reputation: 356

To put it simply: when you execute double randomDouble = Integer.MAX_VALUE + rand.nextInt((max - min) + 1); the part that is actually overflowing (as an Integer, thus taking a negative value) is just Integer.MAX_VALUE + rand.nextInt((max - min) + 1) which is subsequently casted to double.

Upvotes: 1

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