Implementation of Stack (in vector) in Java

StackVector.java

/**
 * @file
 *  Stack.
 * 
 * Implementation with vector.
 * It's used nested class to improve encapsulation.
 *
 * @author Pedro Furtado
 */

public class StackVector {

	/**
	 * Properties of stack.
	 */
	private int max =  5;

	private int top = -1;

	private StackNode[] A = new StackNode[this.max];

	/**
	 * Element of stack.
	 */
	class StackNode {

		public int key;

		public StackNode next = null;
	}

	/**
	 * Default constructor method.
	 */
	StackVector() {

		for (int i = 0; i < this.max; i++) {

			this.A[i] = new StackNode();
		}
	}

	/**
	 * Empty method.
	 *
	 * Determines if the stack is empty, i.e., if it does not have elements inside.
	 *
	 * @return boolean
	 */
	public boolean is_empty() {

		return this.top == -1;
	}

	/**
	 * Full method.
	 *
	 * Determines if the stack is full, i.e., if all vector indexes are filled with stack elements.
	 *
	 * @return boolean
	 */
	public boolean is_full() {

		return this.top == this.max - 1;
	}

	/**
	 * Push method.
	 *
	 * Add an element to the top position of the vector stack.
	 *
	 * @param int key
	 *  Integer key.
	 * @return void
	 */
	public void push(int key) {

		if (this.is_full()) return;

		this.top++;

		this.A[this.top].key = key;
	}

	/**
	 * Pop method.
	 *
	 * Remove the element on the top position of vector stack.
	 *
	 * @return int
	 *  Stack element key of -5 if is empty.
	 */
	public int pop() {

		if (this.is_empty()) return -5;

		int key = this.A[this.top].key;

		this.top--;

		return key;
	}

	/**
	 * Size method.
	 *
	 * Determines the size of the stack, i.e., the number of elements of the stack.
	 *
	 * @return int
	 *  Number of elements in stack.
	 */
	public int size() {

		return this.top + 1;
	}

	/**
	 * toString method.
	 *
	 * Provide some visual funcionality to see the elements inside the stack.
	 *
	 * @return String
	 *  Representation of the stack in the moment by a string.
	 */
	public String toString() {

		if (this.is_empty()) return "Empty stack vector.";

		String description = "Stack Vector: [ ";

		for (int i = 0; i <= this.top; i++) {

			description += this.A[i].key + ", ";
		}

		description += " ]";

		return description;
	}
}