CODEWITHSUNDEEP
javamath
zippy
zippy

Reputation: 1011

Java math function to convert positive int to negative and negative to positive?

Is there a Java function to convert a positive int to a negative one and a negative int to a positive one?

I'm looking for a reverse function to perform this conversion:

-5  ->  5
 5  -> -5

Upvotes: 82

Views: 277042

Answers (14)

Paul
Paul

Reputation: 1041

Adding my 2 cents.

public static int reverse(int value) {
    return Integer.valueOf(0).compareTo(value * value) * value;
}

Tip : you can replace 0 with java.math.BigDecimal.ZERO or java.math.BigInteger.ZERO.

To test it (i.e. on tio.run) :

public class Main {
    public static void main(String[] args) {
        print(5);
        print(-5);
    }

    public static int reverse(int value) {
        return Integer.valueOf(0).compareTo(value * value) * value;
    }

    public static void print(int i) {
        System.out.printf("\nReversed %s to %s .", i, reverse(i));
    }
}

Prints :

Reversed 5 to -5 .
Reversed -5 to 5 .

Processing time : 0.106 s.

Instead of doing the x to -x thing.

public class Main {
    public static void main(String[] args) {
        int x = 5;
        print(x);
        x = -5;
        print(x);
    }

    public static void print(int i) {
        System.out.printf("\nReversed %s to %s .", i, -i);
    }
}

Processing time : 0.108 s

Upvotes: 0

Aamer
Aamer

Reputation: 622

For converting a negative number to positive. Simply use Math.abs() inbuilt function.

int n = -10;
n = Math.abs(n);

All the best!

Upvotes: 0

Emmanuel Loisance
Emmanuel Loisance

Reputation: 726

In kotlin you can use unaryPlus and unaryMinus

input = input.unaryPlus()

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/unary-plus.html https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-int/unary-minus.html

Upvotes: -2

Jebjosh
Jebjosh

Reputation: 93

The easiest thing to do is 0- the value

for instance if int i = 5;

0-i would give you -5

and if i was -6;

0- i would give you 6

Upvotes: 5

Stefan Steiger
Stefan Steiger

Reputation: 82136

Necromancing here.
Obviously, x *= -1; is far too simple.

Instead, we could use a trivial binary complement:

number = ~(number - 1) ;

Like this:

import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
    public static void main (String[] args) throws java.lang.Exception
    {
        int iPositive = 15;
        int iNegative = ( ~(iPositive - 1) ) ; // Use extra brackets when using as C preprocessor directive ! ! !...
        System.out.println(iNegative);

        iPositive =  ~(iNegative - 1)  ;
        System.out.println(iPositive);

        iNegative = 0;
        iPositive = ~(iNegative - 1);
        System.out.println(iPositive);


    }
}

That way we can ensure that mediocre programmers don't understand what's going on ;)

Upvotes: 6

Thiago Araújo
Thiago Araújo

Reputation: 820

You can use Math:

int x = Math.abs(-5);

Upvotes: -4

K.D. Code
K.D. Code

Reputation: 79

original *= -1;

Simple line of code, original is any int you want it to be.

Upvotes: 5

lovos
lovos

Reputation: 21

You can use the minus operator or Math.abs. These work for all negative integers EXCEPT for Integer.MIN_VALUE! If you do 0 - MIN_VALUE the answer is still MIN_VALUE.

Upvotes: 1

old grouch
old grouch

Reputation: 101

Yes, as was already noted by Jeffrey Bosboom (Sorry Jeffrey, I hadn't noticed your comment when I answered), there is such a function: Math.negateExact.

and

No, you probably shouldn't be using it. Not unless you need a method reference.

Upvotes: 8

Salix alba
Salix alba

Reputation: 7824

No such function exists or is possible to write.

The problem is the edge case Integer.MIN_VALUE (-2,147,483,648 = 0x80000000) apply each of the three methods above and you get the same value out. This is due to the representation of integers and the maximum possible integer Integer.MAX_VALUE (-2,147,483,647 = 0x7fffffff) which is one less what -Integer.MIN_VALUE should be.

Upvotes: 6

Bohemian
Bohemian

Reputation: 424953

Just use the unary minus operator:

int x = 5;
...
x = -x; // Here's the mystery library function - the single character "-"

Java has two minus operators:

  • the familiar arithmetic version (eg 0 - x), and
  • the unary minus operation (used here), which negates the (single) operand

This compiles and works as expected.

Upvotes: 57

Shivanshu Goyal
Shivanshu Goyal

Reputation: 1452

Another method (2's complement):

public int reverse(int x){
    x~=x;
    x++;
    return x;
}

It does a one's complement first (by complementing all the bits) and then adds 1 to x. This method does the job as well.

Note: This method is written in Java, and will be similar to a lot of other languages

Upvotes: 11

user207421
user207421

Reputation: 310840

x = -x;

This is probably the most trivial question I have ever seen anywhere.

... and why you would call this trivial function 'reverse()' is another mystery.

Upvotes: 116

FailedDev
FailedDev

Reputation: 26920

What about x *= -1; ? Do you really want a library function for this?

Upvotes: 288

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