Stack类源码解析

Stack
1.通过继承Vector类实现栈功能
2.增加同步方法，线程安全，效率低

package java.util;

public
class Stack<E> extends Vector<E> {
/**
 * 创建栈
 */
    public Stack() {
    }

/**
 * 入栈
 * @return the <code>item</code> argument.
 * @see java.util.Vector#addElement
 */
    public E push(E item) {
        addElement(item);

return item;
    }

/**
 * 出栈
 *
 * @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;
    }

/**
 * 栈顶元素
 *
 * @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);
    }

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

/**
 * 查找元素 o 的id 
 *
 * @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;
    }

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