List之Stack源码分析

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源码版本为JDK1.7.0_75。

该类继承自Vector，说明该类是可克隆的、可序列化的，且是同步的。

publicclass Stack<E> extends Vector<E>

构造函数

public Stack() {    }

入栈

    /**     * 将一个元素放入栈顶，通过vector类的addElement方法实现     * Pushes an item onto the top of this stack. This has exactly     * the same effect as:     * <blockquote><pre>     * addElement(item)</pre></blockquote>     *     * @param   item   the item to be pushed onto this stack.     * @return  the <code>item</code> argument.     * @see     java.util.Vector#addElement     */    public E push(E item) {        addElement(item);         return item;    }

出栈

    /**     * 删除栈顶元素并将其返回，使用peek方法获取栈顶元素，使用vector类的removeElementAt方法完成元素的删除     * 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 <tt>Vector</tt> object).     * @throws  EmptyStackException  if this stack is empty.     */    public synchronized E pop() {        E       obj;        int     len = size();         obj = peek();        removeElementAt(len - 1);         return obj;    }    /**     * 查看栈顶元素，但不将其从栈顶删除，使用vector类的elementAt方法实现。     * 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 <tt>Vector</tt> 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);    }

是否为空

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

搜索

    /**     * vector从n-1到0对应栈顶到栈底，因此在搜索时，应使用lastIndexOf方法     * Returns the 1-based position where an object is on this stack.     * If the object <tt>o</tt> 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 <tt>1</tt>. The <tt>equals</tt>     * method is used to compare <tt>o</tt> 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 <code>-1</code>     *          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;    }

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