CC1.8.java

    public boolean isRotate(String s1, String s2) {
        if(s1 == null || s2 == null || s1.isEmpty() || s2.isEmpty() || s1.length() != s2.length())
            return false;
        else
            return isSubstring(s1+s1, s2);
    }
    
    private boolean isSubstring(String s1, String s2) {
        return s1.contains(s2);
    }