Java Floodit game public class GenericArrayStack<E> implements Stack<E> { privat

Question

Java Floodit game

public class GenericArrayStack<E> implements Stack<E> {

  

private E[] elems;
private int top;
  
@SuppressWarnings( "unchecked" )

  
public GenericArrayStack( int capacity ) {
   elems = (E[]) new Object[ capacity ];
  
   top = 0;
}

  
public boolean isEmpty() {
   return top == 0;
}

public void push( E elem ) {
  
   elems[ top ] = elem;
   top++;

}
public E pop() {
  

   E saved;

   top--;
   saved = elems[ top ];
   elems[ top ] = null;

   return saved;
}

public E peek() {
  

   return elems[ top-1 ];
}
}

In the previous version of the game, we have been using a stack implementation that was based on an array. That implementation did not include precondition checks and did not throw any exceptions. We will first switch from an array implementation to a linked element implementation, and add the proper checks and exceptions. 1.1 Linked Stack Implementation (5 marks) You must replace the GenericArrayStack class with a GenericLinkedStack class. Follow the steps seen in class for this. 1.2 Defining new exception types and checking preconditions (5 marks) You must create a new unchecked exception type called EmptyStackException.

Explanation / Answer

import java.util.NoSuchElementException; /** * The class GenericLinkedStack represents the linked stack data structure. * It supports four operations: isEmpty, push, peek, and pop. * The elements of this linked stack are of type Elem, which is defined in an inner class of GenericLinkedStack. */ public class GenericLinkedStack implements Stack4 { /** * The static class Elem represents a node of the linked stack data structure. * It has references to its payload (info) and its next value (next). */ private static class Elem { private E info; private Elem next; private Elem(E info, Elem next) { if(info == null){ throw new NullPointerException("Attempting to set payload to null."); } this.info = info; this.next = next; } } /** * top element of the GenericLinkedStack. */ private Elem top; /** * Tests if this GenericLinkedStack is empty. * * @return true if this GenericLinkedStack is empty; and false otherwise. */ public boolean isEmpty() { return (top == null); } /** * Puts an element onto the top of this GenericLinkedStack. * * @param info the element be put onto the top of this GenericLinkedStack. */ public void push(T info) { if (info == null){ throw new NullPointerException("The element being pushed to the stack is null"); } Elem previousTop = top; top = new Elem(info, previousTop); } /** * Returns a reference to the top element; does not change * the state of this GenericLinkedStack. * * @return The top element of this GenericLinkedStack without removing it. */ public T peek() { if (isEmpty()) { throw new EmptyStackException2("Stack is empty"); } return top.info; } /** * Removes and returns the element at the top of this GenericLinkedStack. * * @return The top element of this GenericLinkedStack. */ public T pop() { if (isEmpty()) { throw new EmptyStackException2("Stack is empty"); } T saved = top.info; top = top.next; return saved; } }

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