What types of monitoring objects are used in Java and how do they function?

In Java, a monitor is a synchronization mechanism built into each object that allows managing access to shared resources in a multithreaded environment.

Types of monitor objects in Java:

1. Object's intrinsic monitor — each object in Java has an associated monitor. The synchronized keyword is used to acquire and release this monitor.

2. ReentrantLock from the java.util.concurrent.locks package — a more flexible locking mechanism that also implements the monitor concept but with additional features (e.g., attempting to acquire the lock with a timeout).

How they work:

• When a thread enters a synchronized block, it acquires the object's monitor.
• Other threads trying to enter the same block or method will be blocked until the monitor is released.
• This ensures mutual exclusion (mutex), preventing concurrent access to critical sections.

Example of using the intrinsic monitor:

public class Counter {
    private int count = 0;

    public synchronized void increment() {
        count++;
    }

    public synchronized int getCount() {
        return count;
    }
}

Here, the increment and getCount methods are synchronized, ensuring correctness when accessed from multiple threads.