为什么Synchronized块比同步方法更好? [英] Why is Synchronized block better than synchronized method?
问题描述
我已开始在线程中学习同步。
I have started learning synchronization in threading.
同步方法:
public class Counter{
private static int count = 0;
public static synchronized int getCount(){
return count;
}
public synchronized setCount(int count){
this.count = count;
}
}
同步块:
public class Singleton{
private static volatile Singleton _instance;
public static Singleton getInstance(){
if(_instance == null){
synchronized(Singleton.class){
if(_instance == null)
_instance = new Singleton();
}
}
return _instance;
}
我应该何时使用同步方法和同步块?
为什么同步块比同步方法更好?
When should I use Synchronized method and Synchronized block ? Why is Synchronized block better than synchronized method ?
推荐答案
这不是一个更好的问题,只是不同。
同步方法时,您实际上正在同步对象本身。对于静态方法,您将同步到对象的类。所以以下两段代码执行相同的方式:
When you synchronize a method, you are effectively synchronizing to the object itself. In the case of a static method, you're synchronizing to the class of the object. So the following two pieces of code execute the same way:
public synchronized int getCount() {
// ...
}
这就像你写的一样。
public int getCount() {
synchronized (this) {
// ...
}
}
如果要控制与特定对象的同步,或者只想要部分要与对象同步的方法,然后指定 synchronized
块。如果在方法声明中使用 synchronized
关键字,它会将整个方法同步到对象或类。
If you want to control synchronization to a specific object, or you only want part of a method to be synchronized to the object, then specify a synchronized
block. If you use the synchronized
keyword on the method declaration, it will synchronize the whole method to the object or class.
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