Intersection of two strings in Java

Question

Need a Java function to find intersection of two strings. i.e. characters common to the strings.

Example:

String s1 = new String("Sychelless");
String s2 = new String("Sydney");

Answer 1

s1.contains(s2) returns true;
s1.indexOf(s2) returns 0. 
s1.indexOf("foo") returns -1

For more sophisticated cases use class Pattern.

Answer 2

More detail on saugata's response (appeared while I was writing this): -

public static void main(String[] args) {
    String s1 = "Seychelles";
    String s2 = "Sydney";
    Set<Character> ss1 = toSet(s1);
    ss1.retainAll(toSet(s2));
    System.out.println(ss1);
}

public static Set<Character> toSet(String s) {
    Set<Character> ss = new HashSet<Character>(s.length());
    for (char c : s.toCharArray())
        ss.add(Character.valueOf(c));
    return ss;
}

Answer 3

Using HashSet<Character>:

HashSet<Character> h1 = new HashSet<Character>(), h2 = new HashSet<Character>();
for(int i = 0; i < s1.length(); i++)                                            
{
  h1.add(s1.charAt(i));
}
for(int i = 0; i < s2.length(); i++)
{
  h2.add(s2.charAt(i));
}
h1.retainAll(h2);
Character[] res = h1.toArray(new Character[0]);

This is O(m + n), which is asymptotically optimal.