堆栈链表实现方式（java）

// ListStack class
//
// CONSTRUCTION: with no initializer
//
// ******************PUBLIC OPERATIONS*********************
// void push( x )         --> Insert x
// void pop( )            --> Remove most recently inserted item
// Object top( )          --> Return most recently inserted item
// Object topAndPop( )    --> Return and remove most recent item
// boolean isEmpty( )     --> Return true if empty; else false
// void makeEmpty( )      --> Remove all items
// ******************ERRORS********************************
// top, pop, or topAndPop on empty stack
/**
* List-based implementation of the stack.
* @author Mark Allen Weiss
*/
public class ListStack implements Stack {
    /**
     * Construct the stack.
     */
    public ListStack( ) {
        topOfStack = null;
    }
    /**
     * Test if the stack is logically empty.
     * @return true if empty, false otherwise.
     */
    public boolean isEmpty( ) {
        return topOfStack == null;
    }
    /**
     * Make the stack logically empty.
     */
    public void makeEmpty( ) {
        topOfStack = null;
    }
    /**
     * Insert a new item into the stack.
     * @param x the item to insert.
     */
    public void push( Object x ) {
        topOfStack = new ListNode( x, topOfStack );
    }
    /**
     * Remove the most recently inserted item from the stack.
     * @throws UnderflowException if the stack is empty.
     */
    public void pop( ) {
        if( isEmpty( ) )
            throw new UnderflowException( "ListStack pop" );
        topOfStack = topOfStack.next;
    }
    /**
     * Get the most recently inserted item in the stack.
     * Does not alter the stack.
     * @return the most recently inserted item in the stack.
     * @throws UnderflowException if the stack is empty.
     */
    public Object top( ) {
        if( isEmpty( ) )
            throw new UnderflowException( "ListStack top" );
        return topOfStack.element;
    }
    /**
     * Return and remove the most recently inserted item
     * from the stack.
     * @return the most recently inserted item in the stack.
     * @throws UnderflowException if the stack is empty.
     */
    public Object topAndPop( ) {
        if( isEmpty( ) )
            throw new UnderflowException( "ListStack topAndPop" );
        Object topItem = topOfStack.element;
        topOfStack = topOfStack.next;
        return topItem;
    }
    private ListNode topOfStack;
}
/**
* Exception class for access in empty containers
* such as stacks, queues, and priority queues.
* @author Mark Allen Weiss
*/
public class UnderflowException extends RuntimeException {
    /**
     * Construct this exception object.
     * @param message the error message.
     */
    public UnderflowException( String message ) {
        super( message );
    }
}
// Stack interface
//
// ******************PUBLIC OPERATIONS*********************
// void push( x )         --> Insert x
// void pop( )            --> Remove most recently inserted item
// Object top( )          --> Return most recently inserted item
// Object topAndPop( )    --> Return and remove most recent item
// boolean isEmpty( )     --> Return true if empty; else false
// void makeEmpty( )      --> Remove all items
// ******************ERRORS********************************
// top, pop, or topAndPop on empty stack
/**
* Protocol for stacks.
* @author Mark Allen Weiss
*/
public interface Stack {
    /**
     * Insert a new item into the stack.
     * @param x the item to insert.
     */
    void    push( Object x );
    /**
     * Remove the most recently inserted item from the stack.
     * @exception UnderflowException if the stack is empty.
     */
    void    pop( );
    /**
     * Get the most recently inserted item in the stack.
     * Does not alter the stack.
     * @return the most recently inserted item in the stack.
     * @exception UnderflowException if the stack is empty.
     */
    Object  top( );
    /**
     * Return and remove the most recently inserted item
     * from the stack.
     * @return the most recently inserted item in the stack.
     * @exception UnderflowException if the stack is empty.
     */
    Object  topAndPop( );
    /**
     * Test if the stack is logically empty.
     * @return true if empty, false otherwise.
     */
    boolean isEmpty( );
    /**
     * Make the stack logically empty.
     */
    void    makeEmpty( );
}
// Basic node stored in a linked list
// Note that this class is not accessible outside
// of package weiss.nonstandard
class ListNode {
    // Constructors
    public ListNode( Object theElement ) {
        this( theElement, null );
    }
    public ListNode( Object theElement, ListNode n ) {
        element = theElement;
        next    = n;
    }
    public Object   element;
    public ListNode next;
}