What is the difference between synchronized and lock in Java?

What is the difference between synchronized and lock in Java?

In Java, synchronized and lock are two different mechanisms used to achieve thread synchronization, which ensures that multiple threads access shared resources concurrently without conflicts or data corruption.

Synchronized

The synchronized keyword is a low-level locking mechanism in Java that allows only one thread to execute a block of code at a time. When a thread enters a synchronized block, it acquires the lock associated with the object on which the method is declared. This lock is known as the intrinsic lock or monitor lock.

Here are the key characteristics of synchronized:

Lock

The lock mechanism in Java is a more explicit and flexible way to manage locks compared to synchronized. A ReentrantLock (a specific type of Lock) provides fine-grained control over locking and unlocking, allowing for more complex concurrency scenarios.

Here are the key characteristics of lock:

Key differences

In summary:

In practice, synchronized is often used for simple synchronization needs, while lock is typically employed in more advanced concurrency scenarios or when custom locking logic is required.

What is the difference between synchronized and lock in Java?

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In Java, synchronization mechanisms are crucial for ensuring that multiple threads can safely access shared resources while maintaining data integrity. Two fundamental concepts used to achieve thread-safe programming are synchronized and lock. Understanding the differences between these two will enable you to write more effective and efficient multithreaded programs.

Synchronized

The synchronized keyword is used to ensure that only one thread can execute a block of code at a time. It is often used with methods, blocks of code, or classes to achieve mutual exclusion, which ensures that only one thread can access a shared resource simultaneously. When a thread tries to enter a synchronized block, it will be blocked until the current executing thread exits the block.

Here are some key characteristics of synchronized:

Example:

public class Counter {
private int count = 0;
public synchronized void increment() {
count++;
}
public synchronized int getCount() {
return count;
}
}

In this example, the increment and getCount methods are synchronized, ensuring that only one thread can modify the counter's state at a time.

Lock

Java 5 introduced the java.util.concurrent.locks package, which provides more fine-grained control over thread synchronization. The ReentrantLock class allows you to create your own locks and apply custom locking strategies.

Here are some key characteristics of lock:

Example:

import java.util.concurrent.locks.ReentrantLock;
public class Counter {
private int count = 0;
private final ReentrantLock lock = new ReentrantLock();
public void increment() {
lock.lock();
try {
count++;
} finally {
lock.unlock();
}
}
public int getCount() {
lock.lock();
try {
return count;
} finally {
lock.unlock();
}
}
}

In this example, the ReentrantLock is used to manually acquire and release the lock when incrementing or retrieving the counter's state.

Key differences

To summarize:

When deciding between synchronized and lock, consider the complexity and specific requirements of your multithreaded program. If you need fine-grained control or custom locking behavior, use locks; if you require automatic locking and mutual exclusion, choose synchronized.