Stack

stack

下面看下Java的stack源码， 具体API使用，我就不介绍了。

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
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 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
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 */

package java.util;

/**
 * The Stack class represents a last-in-first-out
 * (LIFO) stack of objects. It extends class Vector with five
 * operations that allow a vector to be treated as a stack. The usual
 * push and pop operations are provided, as well as a
 * method to peek at the top item on the stack, a method to test
 * for whether the stack is empty, and a method to search
 * the stack for an item and discover how far it is from the top.
 * 

 * When a stack is first created, it contains no items.
 *
 * 
A more complete and consistent set of LIFO stack operations is
 * provided by the {@link Deque} interface and its implementations, which
 * should be used in preference to this class.  For example:
 * 
   {@code
 *   Deque stack = new ArrayDeque();}
 *
 * @author  Jonathan Payne
 * @since   JDK1.0
 */
public
class Stack extends Vector {
    /**
     * Creates an empty Stack.
     */
    public Stack() {
    }

    /**
     * Pushes an item onto the top of this stack. This has exactly
     * the same effect as:
     * 
     * addElement(item)
     *
     * @param   item   the item to be pushed onto this stack.
     * @return  the item argument.
     * @see     java.util.Vector#addElement
     */
    public E push(E item) {
        addElement(item);

        return item;
    }

    /**
     * Removes the object at the top of this stack and returns that
     * object as the value of this function.
     *
     * @return  The object at the top of this stack (the last item
     *          of the Vector object).
     * @throws  EmptyStackException  if this stack is empty.
     */
    public synchronized E pop() {
        E       obj;
        int     len = size();

        obj = peek();
        removeElementAt(len - 1);

        return obj;
    }

    /**
     * Looks at the object at the top of this stack without removing it
     * from the stack.
     *
     * @return  the object at the top of this stack (the last item
     *          of the Vector object).
     * @throws  EmptyStackException  if this stack is empty.
     */
    public synchronized E peek() {
        int     len = size();

        if (len == 0)
            throw new EmptyStackException();
        return elementAt(len - 1);
    }

    /**
     * Tests if this stack is empty.
     *
     * @return  true if and only if this stack contains
     *          no items; false otherwise.
     */
    public boolean empty() {
        return size() == 0;
    }

    /**
     * Returns the 1-based position where an object is on this stack.
     * If the object o occurs as an item in this stack, this
     * method returns the distance from the top of the stack of the
     * occurrence nearest the top of the stack; the topmost item on the
     * stack is considered to be at distance 1. The equals
     * method is used to compare o to the
     * items in this stack.
     *
     * @param   o   the desired object.
     * @return  the 1-based position from the top of the stack where
     *          the object is located; the return value -1
     *          indicates that the object is not on the stack.
     */
    public synchronized int search(Object o) {
        int i = lastIndexOf(o);

        if (i >= 0) {
            return size() - i;
        }
        return -1;
    }

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = 1224463164541339165L;
}

由于直接使用 Vector API接口，所以很简单。

比如，底层数据扩容等，都没有介绍,如果感兴趣，可以底层源码看看，也很简单。

下面使用 go 实现一个

package stack

import (
    "container/list"
)

// stack struct
type Stack struct {
    list *list.List
}

// get a stack
func NewStack() *Stack {
    list := list.New()
    return &Stack{list}
}

// stack method
// push  list back end
func (s *Stack) Push(value interface{}) {
    s.list.PushBack(value)
}

// pop  back element
func (s *Stack) Pop() interface{} {
    e := s.list.Back()
    if e != nil {
        s.list.Remove(e)
        return e.Value
    }
    return nil

}

func (s *Stack) Peek() interface{} {
    e := s.list.Back()
    if e != nil {
        return e.Value
    }
    return nil
}

func (s *Stack) Len() int {
    return s.list.Len()
}

func (s *Stack) Empty() bool {
    return s.list.Len() == 0
}