Stack based LinkedList implementation 1. Go to the List interface and add a method to get the value of the head You should also add the implementation of the method the the LinkedList and DoublyLinkedList classes. public E getHead()\{ if(! empty()) return head. data; return null; \} 2. The Stack class class Stack implements StackADT \{ // ToDo \} Implementing the checkBalance method Given an expression string exp, write a program to examine whether the pairs and the orders of "\{", "\}," "(", ")", "[", "]" are correct in exp. static boolean checkBalance(String expr) \{ // ToDo \}