check for string rotation in java

IsRotation.java

public class IsRotation {

    public static void main(String[] args) {
        String a = "ABCD";
        String b = "DABC";



        System.out.println(isRotation(a,b));

        String c = "DCAB";

        System.out.println(isRotation(a,c));

    }

    private static boolean isRotation(String a, String b) {

        if(a.length() == b.length() && (( a + a).indexOf(b) ) != -1){
            return true;
        }
        return false;
    }

}