从下面三个层面去分析
1.Stack的简介
2.Stack的数据结构
3.Stack的源码分析
4.Stack的示例
在这篇博客中(进入Vector详细介绍)已经学习Vector,从数据结构这一节,可以看到Stack是继承于Vector的,所以学习Stack更容易学习和理解了,想要学习Stack肯定首先把Vector搞清楚,那么学习起来这一章节就很简单了。只是提供了Stack特有的API,突显了出了栈的特性,Stack这个类也是基于数组数据结构实现的。
1.Stack的简介
Stack 特性:(FILO, First In Last Out,先进后出)
util工具包中的Stack是继承于Vector(矢量队列)的,由于Vector是通过数组实现的,这就意味着,Stack也是通过数组实现的,而非链表。当然,我们也可以将LinkedList当作栈来使用!在【Vector 详细介绍(源码分析)】已经学习Vector,从下文数据结构这一节,可以看到Stack是继承于Vector的,所以学习Stack更容易学习和理解了,想要学习Stack肯定首先把Vector搞清楚,那么学习起来这一章节就很简单了。只是提供了Stack特有的API,突显了出了栈的特性,Stack这个类也是基于数组数据结构实现的。
2.Stack的数据结构
java.lang.Object
↳ java.util.AbstractCollection<E>
↳ java.util.AbstractList<E>
↳ java.util.Vector<E>
↳ java.util.Stack<E>
public
class Stack<E> extends Vector<E>
Stack的API
Stack区别于常规的集合,Stack是栈,它常用的API如下:
boolean empty()
synchronized E peek()
synchronized E pop()
E push(E object)
synchronized int search(Object o)
由于Stack和继承于Vector,因此它也包含Vector中的全部API。
3.Stack的源码分析
package java.util;
/**
* The <code>Stack</code> class represents a last-in-first-out
* (LIFO) stack of objects. It extends class <tt>Vector</tt> with five
* operations that allow a vector to be treated as a stack. The usual
* <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a
* method to <tt>peek</tt> at the top item on the stack, a method to test
* for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt>
* the stack for an item and discover how far it is from the top.
* <p>
* When a stack is first created, it contains no items.
*
* <p>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:
* <pre> {@code
* Deque<Integer> stack = new ArrayDeque<Integer>();}</pre>
*
* @author Jonathan Payne
* @since JDK1.0
*/
public
class Stack<E> extends Vector<E> {
/**
* Creates an empty Stack.
*/
//构造函数
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
*/
// push函数:将元素存入栈顶,push
public E push(E item) {
// 将元素存入栈顶。
// addElement()的实现在Vector.java中
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).
* @throws EmptyStackException if this stack is empty.
*/
// pop函数:返回栈顶元素,并将其从栈中删除
public synchronized E pop() {
E obj;
int len = size();
obj = peek();
// 删除栈顶元素,removeElementAt()的实现在Vector.java中
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).
* @throws EmptyStackException if this stack is empty.
*/
// peek函数:返回栈顶元素,不执行删除操作
public synchronized E peek() {
int len = size();
if (len == 0)
throw new EmptyStackException();
// 返回栈顶元素,elementAt()具体实现在Vector.java中
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.
*/
// 栈是否为空
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.
*/
// 查找“元素o”在栈中的位置:由栈底向栈顶方向数
public synchronized int search(Object o) {
// 获取元素索引,elementAt()具体实现在Vector.java中
int i = lastIndexOf(o);
if (i >= 0) {
return size() - i;
}
return -1;
}
//Stack版本id,这个主要用于版本升级控制
/** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = 1224463164541339165L;
}
(1) Stack实际上也是通过数组去实现的。
执行push时(即,将元素推入栈中),是通过将元素追加的数组的末尾中。
执行peek时(即,取出栈顶元素,不执行删除),是返回数组末尾的元素。
执行pop时(即,取出栈顶元素,并将该元素从栈中删除),是取出数组末尾的元素,然后将该元素从数组中删除。
(2) Stack继承于Vector,Vector拥有的属性和功能,Stack都拥有。
4.Stack的示例
package com.wy.concurrent.collection.stack;
import java.util.Iterator;
import java.util.List;
import java.util.Stack;
/**
* @author wy
* @Classname StackTest
* @Description 栈 (后进先出 基于数组实现和LinkedList中的push和pop方法是有区别的,
* 看源码可知 stack的push是放在末尾,LinkedList的push方法是把元素放在队头)
*
* 限定仅在表尾进行插入和删除操作的线性表
* 这一端被称为栈顶,相对地,把另一端称为栈底。
* 向一个栈插入新元素又称作进栈、入栈或压栈
* 它是把新元素放到栈顶元素的上面,使之成为新的栈顶元素;从一个栈删除元素又称作出栈或退栈,它是把栈顶元素删除掉,使其相邻的元素成为新的栈顶元素
* @Date 2019/8/25 15:35
* @company
*/
public class StackTest {
public static void main(String[] args) {
Stack stack = new Stack();
// 将1,2,3,4,5添加到栈中
for(int i=1; i<6; i++) {
stack.push(String.valueOf(i));
}
// 遍历并打印出该栈
iteratorThroughRandomAccess(stack) ;
// 查找“2”在栈中的位置,并输出
int pos = stack.search("2");
System.out.println("the postion of 2 is:"+pos);
// pop栈顶元素之后,遍历栈
stack.pop();
iteratorThroughRandomAccess(stack) ;
// peek栈顶元素之后,遍历栈
String val = (String)stack.peek();
System.out.println("peek:"+val);
iteratorThroughRandomAccess(stack) ;
// 通过Iterator去遍历Stack
iteratorThroughIterator(stack) ;
}
/**
* 通过快速访问遍历Stack
*/
public static void iteratorThroughRandomAccess(List list) {
String val = null;
for (int i=0; i<list.size(); i++) {
val = (String)list.get(i);
System.out.print(val+" ");
}
System.out.println();
}
/**
* 通过迭代器遍历Stack
*/
public static void iteratorThroughIterator(List list) {
String val = null;
for(Iterator iter = list.iterator(); iter.hasNext(); ) {
val = (String)iter.next();
System.out.print(val+" ");
}
System.out.println();
}
}