The challenge

Given a number, find its opposite.

Examples:

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1: -1
14: -14
-34: 34

The solution in Java

We return the number itself multiplied by a negative 1.

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public class Solution {
    public static int opposite(int number) {
        return number *= -1;
    }
}

This can be simplified further as:

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public class Solution {
    public static int opposite(int number) {
        return -number;
    }
}

There is also a built in method to help with this if you prefer, called Math.negateExact():

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public class Solution {
    public static int opposite(int number) {
        return Math.negateExact(number);
    }
}

Test cases to validate our solution

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import org.junit.Test;
import static org.junit.Assert.assertEquals;

public class OppositeExampleTests {
  @Test
  public void tests() {
    assertEquals(-1, Solution.opposite(1));
    assertEquals(0, Solution.opposite(0));
    assertEquals(25, Solution.opposite(-25));
  }
}