# Java 互斥量示例 > 原文： [https://javatutorial.net/java-mutex-example](https://javatutorial.net/java-mutex-example) 在更深入地了解互斥量之前，先给出一个示例： 想想一个队列。 不管长短，都没关系。 现在想想一辆正在出售游乐园门票的卡车。 一次一个人可以买票。 该人买了票后，就该排队了。 这个小故事与理解互斥量有什么关系？ 让我解释。  **互斥量允许每个线程具有 1 个许可**。换句话说，一次只能有 1 个线程可以访问资源。 在上面的类比中，两个人不能同时购买门票。互斥量也是如此。 它不是线程，而是人员，而是票证。 同样的事情或多或少.. 互斥量与`Semaphore`略有不同，因此`Semaphore`允许多个线程访问资源。意思是，多个人可以同时购买门票。  ## 构造器 1. `public Semaphore(int permits)`； 2. `public Semaphore(int permits, boolean fair)` 第一个构造函数是我们实际上可以区分互斥量和`Semaphore`的地方。 如果那里有 1 作为参数，则意味着将只允许 1 个线程获取锁。 请记住，由于它没有第二个参数`boolean fair`，因此您正在使`Semaphore`类以任何顺序访问任何线程。 第二个构造函数如果传递`true`（公平），则确保按线程请求访问并在队列中等待的顺序给出访问。 ## 互斥量基本代码实现 ```java import java.util.concurrent.Semaphore; public class MutexDemo { // create a Semaphore instance that makes it so only 1 thread can access resource at a time private static Semaphore mutex = new Semaphore(1); static class ThreadDemo extends Thread { private String name = ""; public ThreadDemo(String name) { this.name = name; } @Override public void run() { try { // check the above mentioned analogy in the article for reference System.out.println("How many people can buy a ticket at a time: " + mutex.availablePermits()); System.out.println(name + " is buying a ticket..."); mutex.acquire(); try { Thread.sleep(1000); System.out.println(name + " is still buying a ticket. How many people can still buy the ticket alongside him: " + mutex.availablePermits()); } finally { mutex.release(); System.out.println(name + " bought the ticket."); System.out.println("How many people can buy tickets after " + name + " has finished buying the ticket: " + mutex.availablePermits()); } } catch (Exception e) { e.printStackTrace(); } } } public static void main(String[] args) { ThreadDemo thread1 = new ThreadDemo("Bob"); thread1.start(); ThreadDemo thread2 = new ThreadDemo("Charlie"); thread2.start(); ThreadDemo thread3 = new ThreadDemo("Christie"); thread3.start(); } } ``` **输出** ```java How many people can buy a ticket at a time: 1 Bob is buying a ticket... How many people can buy a ticket at a time: 0 Charlie is buying a ticket... How many people can buy a ticket at a time: 0 Christie is buying a ticket... Bob is still buying a ticket. How many people can still buy the ticket alongside him: 0 Bob bought the ticket. How many people can buy tickets after Bob has finished buying the ticket: 1 Charlie is still buying a ticket. How many people can still buy the ticket alongside him: 0 Charlie bought the ticket. How many people can buy tickets after Charlie has finished buying the ticket: 1 Christie is still buying a ticket. How many people can still buy the ticket alongside him: 0 Christie bought the ticket. How many people can buy tickets after Christie has finished buying the ticket: 1 ``` 从输出中可以看到，**当有人买票时，没有其他人可以买**。这是显示以下内容的行之一： Bob 仍在买票。 还有多少人可以和他一起买票： **0** 但是，在他“购买”了机票之后，其他人立即购买了机票。 归根结底，它涉及`acquire()`和`release()`。`acquire()`是指该人开始“购买机票”的时间，`release()`是指该人“购买机票”的时间。