栈

  是限定仅在表尾进行插入或删除操作的线性表
  表尾称为栈顶，表头称为栈底
  特点：后进先出

  操作：
1.推入push
2.弹出pop

栈的数组实现：

public class ArrayStack<E> {
    
    private List<E> list = new ArrayList<E>();
    
    public boolean isEmpty(){
        return list.size()==0;
    }
    
    public void push(E element){
        list.add(element);
    }
    
    public void pop(){
        list.remove(list.size()-1);
    }
    
    public E getPop(){
        return list.get(list.size()-1);
    }    
    
    public List<Integer> getElements(){
        List<Integer> result = new ArrayList<Integer>();
        for(E e : list){
            result.add(((Element)e).getValue());
        }
        return result;
    }

}

栈的链表实现：

public class LinkedStack<E>{

    private static class Node<E>{

        E element;
        
        Node<E> next;    
        
        public Node(E element){
            this.element = element;
        }

    }
    
    private Node<E> top = new Node<E>(null);
    
    private int size = 0;
    
    public boolean isEmpty() {
        return size == 0;
    }

    public void push(E element){
        Node<E> newNode = new Node<E>(element);
        if(!isEmpty()){
            newNode.next = getPopNode();
            top.next = newNode;
        }else{
            top.next = newNode;
        }
        size++;
    }
    
    public void pop(){
        if(isEmpty()){
            throw new RuntimeException("The stack is empty");
        }
        Node<E> firstNode = top.next;
        top.next = firstNode.next;
        firstNode.next = null;
        size--;
    }
    
    public E getPop(){
        return getPopNode().element;
    }    
    
    private Node<E> getPopNode(){
        if(isEmpty()){
            throw new RuntimeException("The stack is empty");
        }
        return top.next;
    }
    
    public List<Integer> getElements(){
        if(isEmpty()){
            return null;
        }else{
            List<Integer> elements = new ArrayList<Integer>();
            Node<E> node = (Node<E>) top;
            while(node.next!=null){
                node = node.next;
                elements.add(((Element)node.element).getValue());
            }
            return elements;
        }
    }
    
}