E push(E item)

           把项压入堆栈顶部。

  E pop()

           移除堆栈顶部的对象，并作为此函数的值返回该对象。

  E peek()

           查看堆栈顶部的对象，但不从堆栈中移除它。

  boolean empty()

           测试堆栈是否为空。

  int search(Object o)

           返回对象在堆栈中的位置，以 1 为基数。

 public class Stack<E> extends Vector<E> {

     /**

      * Creates an empty Stack.

      */

     public Stack() {

     }

     /**

      * 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;

     }

     /**

      * 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).

      * @exception  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 <tt>Vector</tt> object).

      * @exception  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  <code>true</code> if and only if this stack contains

      *          no items; <code>false</code> otherwise.

      */

     public boolean empty() {

     return size() == 0;

     }

     /**

      * 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;

     }

     /** use serialVersionUID from JDK 1.0.2 for interoperability */

     private static final long serialVersionUID = 1224463164541339165L;

 }

 public class StackTest {

     public static void main(String[] args) {

         Stack<String> s = new Stack<String>();

         System.out.println("------isEmpty");

         System.out.println(s.isEmpty());

         System.out.println("------push");

         s.push("1");

         s.push("2");

         s.push("3");

         StackTest.t(s);

         System.out.println("------pop");

         String str = s.pop();

         System.out.println(str);

         StackTest.t(s);

         System.out.println("------peek");

         str = s.peek();

         System.out.println(str);

         StackTest.t(s);

         System.out.println("------search");

         int i = s.search("2");

         System.out.println(i);

         i = s.search("1");

         System.out.println(i);

         i = s.search("none");

         System.out.println(i);

     }

     public static void t(Stack<String> s){

         System.out.println("iterator");

         Iterator<String> it = s.iterator();

         while(it.hasNext()){

             System.out.print(it.next()+"    ");

         }

         System.out.println("\n");

     }

 }

 ------isEmpty

 true

 ------push

 iterator:1;2;3;

 ------pop

 3        --栈顶是数组最后一个

 iterator:1;2;

 ------peek

 2        --pop取后删掉，peek只取不删

 iterator:1;2;

 ------search

 1        --以1为基数，即栈顶为1

 2        --和栈顶见的距离为2-1=1

 -1        --不存在于栈中