java - 同步块(synchronized block)等同于静态同步方法？

Question

当您有如下方法时:

public synchronized void addOne() {
    a++;
}

等同于:(如有错误请指正)

public void addOne() {
    synchronized(this) {
        a++;
    }
}

但是下面的方法等同于什么？:

public static synchronized void addOne() {
    a++;
    // (in this case 'a' must be static)
}

什么是与静态同步方法作用相同的同步块(synchronized block)？我知道静态同步方法是在类上同步的，而不是在实例上同步的(因为没有实例)，但是什么是什么语法？

Answer 1

相当于在类对象上加锁。您可以通过在类名后面加上 .class 来获取对类对象的引用。所以，像这样:

synchronized(YourClass.class) {
}

参见 Java Language Specification, Section 8.4.3.6 synchronized Methods :

A synchronized method acquires a lock (§17.1) before it executes. For a class (static) method, the lock associated with the Class object for the method's class is used. For an instance method, the lock associated with this (the object for which the method was invoked) is used.