In Java, synchronized is a keyword used to provide mutual exclusion and ensure that only one thread can access a critical section of code at a time. This helps prevent race conditions and other concurrency-related issues.
There are two ways to use synchronized in Java: as a block or as a method modifier. A synchronized block is used to synchronize access to a specific block of code. A synchronized method is used to synchronize access to an entire method.
Here’s an example of a synchronized block:
class Example {
private Object lock = new Object();
private int count = 0;
public void increment() {
synchronized (lock) {
count++;
}
}
}In this example, the increment() method is synchronized using a synchronized block. The critical section of code is the count++ statement. By synchronizing on the lock object, we ensure that only one thread can access this critical section at a time.
Here’s an example of a synchronized method:
class Example {
private int count = 0;
public synchronized void increment() {
count++;
}
}In this example, the increment() method is synchronized using the synchronized keyword as a method modifier. This means that the entire method is synchronized, and only one thread can execute it at a time.
The main difference between a synchronized block and a synchronized method is the scope of synchronization. With a synchronized block, you can synchronize access to a specific block of code, while with a synchronized method, you synchronize access to the entire method. Additionally, a synchronized block allows you to synchronize on any object, while a synchronized method always synchronizes on the object instance itself.
It’s generally recommended to use synchronized blocks instead of synchronized methods, as this provides finer-grained control over synchronization and can help improve performance. However, there are cases where using a synchronized method may be more convenient or appropriate.