What is the implementation principle of locks in Java?

The implementation principles of locks in Java mainly involve two forms of locks: the synchronized keyword and the Lock interface.

1. The synchronized keyword is the most basic locking mechanism in Java. It achieves locking by using an object’s monitor to acquire and release locks. Each object has an associated monitor, and when a thread enters a synchronized block, it tries to acquire the object’s monitor. If the monitor is already held by another thread, the current thread will be blocked until the monitor is released. The advantage of the synchronized keyword is its simplicity and ease of use, but the downside is that it only supports basic locking operations such as lock reentrancy, waits timeouts, interrupts, etc.
2. The Lock interface is a more flexible and powerful way of implementing locks in Java, providing additional methods for lock operations such as trying to acquire a lock, waiting with a timeout, and responding to interrupts. The Lock interface commonly used implementation classes include ReentrantLock, ReadWriteLock, etc. The implementation principle of the Lock interface is generally based on the AQS (AbstractQueuedSynchronizer) framework, which is used in Java to construct locks and synchronizers by implementing different functionalities through shared and exclusive modes. The advantage of the Lock interface is that it offers more lock operation methods for flexible control of lock acquisition and release, but the disadvantage is that it is relatively complex to use, requiring more code to manage lock operations.

In general, the implementation principle of locks in Java is mainly based on object monitors and the AQS framework, which allow for acquiring and releasing locks. Developers can choose the appropriate lock implementation method based on their needs for concurrent control.