How to use Synchronized in Java

2 years ago
Isabella Edwards
2 minutes

In Java, the Synchronized keyword is used to achieve thread synchronization, ensuring thread safety when multiple threads access shared resources.

The synchronized keyword can be used for synchronizing in the following ways:

  1. Synchronized method: Adding the keyword to the method declaration indicates that the method is a synchronized method. When a thread calls this method, it will obtain the lock of the object, and other threads must wait for the lock to be released before calling the method.

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public synchronized void synchronizedMethod() {
    // 同步代码块
}
  1. Synchronized code block: Add a keyword to a code block to indicate that it is a synchronized block. This block can only be executed by one thread, while other threads must wait for that thread to finish before they can execute.

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public void synchronizedBlock() {
    synchronized (this) {
        // 同步代码块
    }
}
  1. Object Lock: Using the synchronized keyword to lock an object. When a thread acquires the lock of an object, other threads must wait for that thread to release the lock before they can access the object.

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public class SynchronizedObject {
    public synchronized void synchronizedMethod() {
        // 同步方法
    }
}

public class Main {
    public static void main(String[] args) {
        SynchronizedObject obj = new SynchronizedObject();
        synchronized (obj) {
            // 同步代码块
        }
    }
}

It is important to note that the “Synchronized” keyword can only be used for synchronizing instance methods, static methods, and code blocks, but not for variables or other types of code. Additionally, the “Synchronized” keyword is reentrant, meaning that a thread can acquire the same lock multiple times.

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