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源码
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.
*/
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).
* @throws 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).
* @throws 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;
}
注释内容
- Stack 类代表对象的后进先出（LIFO）栈
- 它通过五个操作扩展了 Vector 类，允许 vector 被视为栈
- 提供通用的 push 和 pop 操作，以及一个查看栈顶元素的方法，一个测试栈是否为空的方法，和一个在栈中查找项和发现它离栈顶多远的方法
- 首次创建栈，它不包含任何项
- Deque 接口和它的实现提供了更完整和一致的 LIFO 栈操作，它应该优先于这个类的使用
方法总结
public Stack()：创建一个空栈public E push(E item)：推送项到这个栈的顶部，和addElement(item)具有完全相同的效果public synchronized E pop()：移除这个栈顶部的对象，并且返回这个对象作为这个方法的值public synchronized E peek()：查看栈顶部的对象，不需要从栈中移除public boolean empty()：测试这个栈是否为空public synchronized int search(Object o)：返回对象在这个栈基于 1 的位置，如果对象 o 作为这个栈的一个项出现，这个方法返回离栈顶的距离，栈最顶端的项被视为距离 1，equals方法被用于比较 o 和这个栈的项
使用
模板代码
class StackTest {
public static void main(String[] args) {
Stack<Integer> stack = new Stack<>();
stack.push(1);
stack.push(2);
stack.push(3);
System.out.println("stack.peek()：" + stack.peek());
System.out.println("stack.pop()：" + stack.pop());
System.out.println("stack.peek()：" + stack.peek());
System.out.println("stack.isEmpty()：" + stack.isEmpty());
System.out.println("stack.search(1)：" + stack.search(1));
System.out.println("stack.search(3)：" + stack.search(3));
}
}
结果
stack.peek()：3
stack.pop()：3
stack.peek()：2
stack.isEmpty()：false
stack.search(1)：2
stack.search(3)：-1
