# Useful Method

* **String Class** toCharArray() //get char array of a String charAt(int x) //get a char at the specific index length() //string length length //array size substring(int beginIndex) substring(int beginIndex, int endIndex) String.valueOf()/integer to string String.join(CharSequence delimiter, CharSequence... elements) 1.8
* **Character** Character.isLetterOrDigit(ch)\
  Character.toLowerCase(ch)
* **Integer** Integer.valueOf()//string to integer
* **StringBuffer** StringBuffer(str).reverse();\
  str.replaceAll("\[^A-Za-z0-9]", "")
* **Arrays** Arrays.sort() //sort an array Arrays.toString(char\[] a) //convert to string Arrays.copyOf(T\[] original, int newLength) Arrays.asList(T\[]) System.arraycopy(Object src, int srcPos, Object dest, int destPos, int length)
* **Collections** Collections.reverse(List)
