北京网站建设方案开发公司,网站开发2008,外贸网站外链怎么做,深圳燃气公司招聘信息转载自 java.util.Stack类简介
Stack是一个后进先出#xff08;last in first out#xff0c;LIFO#xff09;的堆栈#xff0c;在Vector类的基础上扩展5个方法而来
Deque#xff08;双端队列#xff09;比起Stack具有更好的完整性和一致性#xff0c;应该被优先使用…转载自 java.util.Stack类简介
Stack是一个后进先出last in first outLIFO的堆栈在Vector类的基础上扩展5个方法而来
Deque双端队列比起Stack具有更好的完整性和一致性应该被优先使用 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。
Stack本身通过扩展Vector而来而Vector本身是一个可增长的对象数组 a growable array of objects那么这个数组的哪里作为Stack的栈顶哪里作为Stack的栈底
答案只能从源代码中寻找jdk1.6
public class StackE extends VectorE { /** * Creates an empty Stack. */ public Stack() { } /** * Pushes an item onto the top of this stack. This has exactly * the same effect as: * blockquotepre * addElement(item)/pre/blockquote * * param item the item to be pushed onto this stack. * return the codeitem/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 ttVector/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 ttVector/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 codetrue/code if and only if this stack contains * no items; codefalse/code otherwise. */ public boolean empty() { return size() 0; } /** * Returns the 1-based position where an object is on this stack. * If the object tto/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 tt1/tt. The ttequals/tt * method is used to compare tto/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;
}
通过peek()方法注释The object at the top of this stack (the last item of the Vector object可以发现数组Vector的最后一位即为Stack的栈顶
pop、peek以及search方法本身进行了同步
push方法调用了父类的addElement方法
empty方法调用了父类的size方法
Vector类为线程安全类
综上Stack类为线程安全类(多个方法调用而产生的数据不一致问题属于原子性问题的范畴)
public class Test { public static void main(String[] args) { StackString s new StackString(); System.out.println(------isEmpty); System.out.println(s.isEmpty()); System.out.println(------push); s.push(1); s.push(2); s.push(3); Test.it(s); System.out.println(------pop); String str s.pop(); System.out.println(str); Test.it(s); System.out.println(------peek); str s.peek(); System.out.println(str); Test.it(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 it(StackString s){ System.out.print(iterator:); IteratorString it s.iterator(); while(it.hasNext()){ System.out.print(it.next();); } System.out.print(\n); }
}
结果
------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2-11 -1 --不存在于栈中 Stack并不要求其中保存数据的唯一性当Stack中有多个相同的item时调用search方法只返回与查找对象equal并且离栈顶最近的item与栈顶间距离见源码中search方法说明
