Find the stray number in Java

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

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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;
  }
}

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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;
  }
}

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import java.util.Arrays;

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

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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);
  }
}