The challenge

When given a string of space-separated words, return the word with the longest length.

If there are multiple words with the longest length, return the last instance of the word with the longest length.

Example:

'red white blue' // returns string value of white
'red blue gold'  // returns gold

The solution in Java code

Option 1:

public class Solution {
  public static String longestWord(String wordString) {
    String longest = "";
    for (String word: wordString.split(" "))
      if (word.length()>=longest.length())
        longest = word;
    return longest;
  }
}

Option 2:

import java.util.Arrays;
public class Solution {
  public static String longestWord(String words) {
    return Arrays.stream(words.split(" "))
          .reduce((x, y) -> x.length() <= y.length() ? y : x).get();
  }
}

Option 3:

import java.util.*;
public class Solution {
  public static String longestWord(String wordString) {
    final String [] ary = wordString.split(" ");
    Arrays.sort(ary, (a,b) -> a.length() >= b.length() ? -1 : 1);
    return ary[0];
  }
}

Test cases to validate our solution

import org.junit.Test;
import static org.junit.Assert.assertEquals;
import org.junit.runners.JUnit4;

public class ExampleSolutionTests {
    @Test
    public void tests() {
      assertEquals("fgh", Solution.longestWord("a b c d e fgh"));
      assertEquals("three", Solution.longestWord("one two three"));
      assertEquals("grey", Solution.longestWord("red blue grey"));
    }
}