Find the stray number in Java

The challenge

You are given an odd-length array of integers, in which all of them are the same, except for one single number.

Complete the method which accepts such an array, and returns that single different number.

The input array will always be valid! (odd-length >= 3)

Examples

[1, 1, 2] ==> 2
[17, 17, 3, 17, 17, 17, 17] ==> 3

The solution in Java code

Option 1:

import java.util.*;

class Solution {
  static int stray(int[] numbers) {
    Map<Integer, Integer> map = new HashMap<>();
    
    for (int i=0; i<numbers.length; i++) {
      Integer def = map.getOrDefault(numbers[i], 0);
      map.put(numbers[i], ++def);
    }
    
    for(Integer key : map.keySet()) {
      System.out.println(key);
      System.out.println(map.get(key));
      if (map.get(key)==1) return key;
    }
    
    return 0;
  }
}

Option 2:

class Solution {
  static int stray(int[] numbers) {
    if (numbers[0] != numbers[1] && numbers[0] != numbers[2]) return numbers[0];
    for (int i : numbers) if (i != numbers[0]) return i;
    return 0;
  }
}

Option 3:

import java.util.Arrays;

class Solution {
  static int stray(int[] numbers) {
    return Arrays.stream(numbers).reduce(0, (a, b) -> a ^ b);
  }
}

Test cases to validate our solution

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

public class SolutionTest {
  
  @Test
  public void simpleArray1() {
    assertEquals(2, getActualFor(1, 1, 2));
  }
  
  @Test
  public void simpleArray2() {
    assertEquals(3, getActualFor(17, 17, 3, 17, 17, 17, 17));
  }
  
  @Test
  public void firstItem() {
    assertEquals(8, getActualFor(8, 1, 1, 1, 1, 1, 1));
  }
  
  @Test
  public void lastItem() {
    assertEquals(0, getActualFor(1, 1, 1, 1, 1, 1, 0));
  }
  
  @Test
  public void middleItem() {
    assertEquals(7, getActualFor(0, 0, 0, 7, 0, 0, 0));
  }
  
  @Test
  public void fifthItem() {
    assertEquals(-6, getActualFor(-21, -21, -21, -21, -6, -21, -21));
  }
  
  @Test
  public void randomSmallArray() {
    int strayNumber = SolutionHelper.randomInt(-10000, 10000);
    int[] array = SolutionHelper.validRandomArray(101, strayNumber);
    assertEquals(strayNumber, getActualFor(array));
  }
  
  @Test
  public void randomBigArray() {
    int strayNumber = SolutionHelper.randomInt(-10000, 10000);
    int[] array = SolutionHelper.validRandomArray(15273, strayNumber);
    assertEquals(strayNumber, getActualFor(array));
  }
  
  private int getActualFor(int... numbers) {
    return Solution.stray(numbers);
  }
}
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