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Use this interface definition to solve this problem.

public interface StackADT<E> { // Stack class ADT /* Clears the stack. */...

X992: Swap Top Two Nodes in Stack

Use this interface definition to solve this problem.

public interface StackADT<E> { // Stack class ADT
  /* Clears the stack. */
  public void clear();

  /* Pushes argument it onto the stack. */
  public boolean push(E it);

  /* Pop and return the value at the top of the stack. */
  public E pop();

  /* Returns the value at the top of the stack. */
  public E topValue();

  /* Returns the number of elements stored in the stack. */
  public int numElements();

  /* Returns true if the stack is empty, false otherwise. */
  public boolean isEmpty();
}

Write a method to swap the top two elements of the stack. If the stack has less than 2 values, then do nothing. Otherwise, modify the stack by swapping the top two elements. The figure below shows an example of what this method should do.

Worth noting:

Do not just create a new stack with these letters, actually modify the one passed as an argument.
You don't know if the stack is implemented with nodes or arrays so you must use the interface definition to modify the stack.
Don't forget to check for special case (less than 2 elements).

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