Easiest Solution in Java 
Code
# Code
```java []
class Solution {
    public String sortVowels(String s) {
        List<Character> vowel = new ArrayList<>();
        for (char ch : s.toCharArray()) {
            if (isVowel(ch))
                vowel.add(ch);
        }

        Collections.sort(vowel);
        int len = s.length(), ind = 0;

        char[] res = new char[len];
        for (int i = 0; i < len; i++) {
            if (isVowel(s.charAt(i)))
                res[i] = vowel.get(ind++);
            else
                res[i] = s.charAt(i);
        }

        return new String(res);
    }

    private boolean isVowel(char ch) {
        return ch == 'A' || ch == 'E' || ch == 'I' || ch == 'O' || ch == 'U' ||
                ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u';
    }
}
```
['String', 'Sorting', 'Java']