JavaAlgorithms/DataStructures/Stacks/NodeStack.java

package DataStructures.Stacks;
/**
 * Implementation of a stack using nodes. Unlimited size, no arraylist.
 *
 * @author Kyler Smith, 2017
 */
public class NodeStack<Item> {

  /** Entry point for the program. */
  public static void main(String[] args) {
    NodeStack<Integer> Stack = new NodeStack<Integer>();

    Stack.push(3);
    Stack.push(4);
    Stack.push(5);
    System.out.println("Testing :");
    Stack.print(); // prints : 5 4 3

    Integer x = Stack.pop(); // x = 5
    Stack.push(1);
    Stack.push(8);
    Integer y = Stack.peek(); // y = 8
    System.out.println("Testing :");
    Stack.print(); // prints : 8 1 4 3

    System.out.println("Testing :");
    System.out.println("x : " + x);
    System.out.println("y : " + y);
  }

  /**
   * Information each node should contain.
   *
   * @value data : information of the value in the node
   * @value head : the head of the stack
   * @value next : the next value from this node
   * @value previous : the last value from this node
   * @value size : size of the stack
   */
  private Item data;

  private static NodeStack<?> head;
  private NodeStack<?> next;
  private NodeStack<?> previous;
  private static int size = 0;

  /** Constructors for the NodeStack. */
  public NodeStack() {}

  private NodeStack(Item item) {
    this.data = item;
  }

  /**
   * Put a value onto the stack.
   *
   * @param item : value to be put on the stack.
   */
  public void push(Item item) {

    NodeStack<Item> newNs = new NodeStack<Item>(item);

    if (this.isEmpty()) {
      NodeStack.setHead(new NodeStack<>(item));
      newNs.setNext(null);
      newNs.setPrevious(null);
    } else {
      newNs.setPrevious(NodeStack.head);
      NodeStack.head.setNext(newNs);
      NodeStack.head.setHead(newNs);
    }

    NodeStack.setSize(NodeStack.getSize() + 1);
  }

  /**
   * Value to be taken off the stack.
   *
   * @return item : value that is returned.
   */
  public Item pop() {

    Item item = (Item) NodeStack.head.getData();

    NodeStack.head.setHead(NodeStack.head.getPrevious());
    NodeStack.head.setNext(null);

    NodeStack.setSize(NodeStack.getSize() - 1);

    return item;
  }

  /**
   * Value that is next to be taken off the stack.
   *
   * @return item : the next value that would be popped off the stack.
   */
  public Item peek() {
    return (Item) NodeStack.head.getData();
  }

  /**
   * If the stack is empty or there is a value in.
   *
   * @return boolean : whether or not the stack has anything in it.
   */
  public boolean isEmpty() {
    return NodeStack.getSize() == 0;
  }

  /**
   * Returns the size of the stack.
   *
   * @return int : number of values in the stack.
   */
  public int size() {
    return NodeStack.getSize();
  }

  /**
   * Print the contents of the stack in the following format.
   *
   * <p>x <- head (next out) y z <- tail (first in) . . .
   */
  public void print() {
    for (NodeStack<?> n = NodeStack.head; n != null; n = n.previous) {
      System.out.println(n.getData().toString());
    }
  }

  /** Getters and setters (private) */
  private NodeStack<?> getHead() {
    return NodeStack.head;
  }

  private static void setHead(NodeStack<?> ns) {
    NodeStack.head = ns;
  }

  private NodeStack<?> getNext() {
    return next;
  }

  private void setNext(NodeStack<?> next) {
    this.next = next;
  }

  private NodeStack<?> getPrevious() {
    return previous;
  }

  private void setPrevious(NodeStack<?> previous) {
    this.previous = previous;
  }

  private static int getSize() {
    return size;
  }

  private static void setSize(int size) {
    NodeStack.size = size;
  }

  private Item getData() {
    return this.data;
  }

  private void setData(Item item) {
    this.data = item;
  }
}