Java implement Stack use Link List DS

Stack.java

/**
 * 實作 Stack
 * 使用 Link List 資料結構
 * 1. Satck 具有 LIFO 後進先出的特性
 * 2. push 和 pop 都在同一端操作，且有個 top 永遠指向頂端
 * @author Cheng-Ting
 *
 */

/**
 * Link List
 * 節點的資料結構
 */
class Node {
    private int val;
    private Node next = null;
    
    public Node(int val, Node next) {
        this.setVal(val);
        this.setNext(next);
    }
    
    public void setVal(int val) {
        this.val = val;
    }
    
    public int getVal() {
        return this.val;
    }
    
    public void setNext(Node next) {
        this.next = next;
    }
    
    public Node getNext() {
        return this.next;
    }
    
    public String toString() {
        return String.valueOf(this.val);
    }
}

/**
 * Stack ADT 結構
 * @author Cheng-Ting
 *
 */
interface stackADT {
    abstract public void createStack();
    abstract public void push(Node node);
    abstract public Node pop();
    abstract public boolean isEmpty();
    abstract public boolean isFull();
}

/**
 * 
 * 實作 Stack 
 * @author Cheng-Ting
 *
 */
public class Stack implements stackADT {
    private Node top = null;
    
    public Stack() {
        this.createStack();
    }
    
    /**
     * 建立 Stack
     */
    public void createStack() {
        this.top = null;
    }
    
    /**
     * 加入節點
     */
    public void push(Node node) {
        if(this.isEmpty()) {
            this.top = node;
        } else {
            node.setNext(this.top);
            top = node;
        }
    }
    
    /**
     * 取出節點
     */
    public Node pop() {
        Node tmp = null;
        if(this.isEmpty()) {
            System.out.println("statck it empty");
        } else {
           tmp = this.top;
           this.top = this.top.getNext();
        }
        return tmp;
    }
    
    /**
     * 是否為空
     */
    public boolean isEmpty() {
        boolean var;
        if(this.top == null) {
            var =  true;
        } else {
            var = false;
        }
        return var;
    }
    
    /**
     * 是否為滿，因為使用 Link List 所以空間不限
     */
    public boolean isFull() {
        return false;
    }
    
    /**
     * 使用方法
     * @param args
     */
    public static void main(String[] args) {
        Stack stack = new Stack();
        stack.push(new Node(1, null));
        stack.push(new Node(2, null));
        stack.push(new Node(3, null));
        System.out.println(stack.pop());
        System.out.println(stack.pop());
        System.out.println(stack.pop());
        System.out.println(stack.pop());
    }
}