这就像其他任何一样类。它可能需要或可能不需要进一步同步。

It's just like any other class. It may or may not need further synchronization.

请考虑以下示例：

public class Singleton {

  private Singleton() {}

  public synchronized static Singleton getInstance() { ... }

  private int counter = 0;

  public void addToCounter(int val) {
    counter += val;
  }
}

如果要从多个线程使用该类， addToCounter（）有竞争条件。解决这个问题的一种方法是使 addToCounter（）同步：

If the class is to be used from multiple threads, addToCounter() has a race condition. One way to fix that is by making addToCounter() synchronized:

  public synchronized void addToCounter(int val) {
    count += val;
  }

还有其他方法可以修复竞争条件，例如使用 AtomicInteger ：

There are other ways to fix the race condition, for example by using AtomicInteger:

  private final AtomicInteger counter = new AtomicInteger(0);

  public void addToCounter(int val) {
    counter.addAndGet(val);
  }

在这里，我们已经修复了竞争条件而没有使用 synchronized 。

Here, we've fixed the race condition without using synchronized.