What is a monitor object in the context of thread synchronization, especially when using wait methods?

In Java, an object monitor is a mechanism that provides mutual exclusion (mutex) for thread synchronization. Each object in Java is associated with a monitor that allows one thread to own the monitor at a specific time.

When a thread enters a synchronized block or method (synchronized), it acquires the object's monitor. Other threads attempting to enter the same block will wait until the monitor is released.

The wait() method is called on an object whose monitor is held by the current thread. It causes the thread to release the monitor and enter a waiting state until another thread calls notify() or notifyAll() on the same object. This enables coordination between threads.

Example:

synchronized (obj) {
    while (!condition) {
        obj.wait(); // thread releases the monitor and waits
    }
    // executes when condition is true
}

Thus, an object monitor is a lock and wait mechanism associated with an object that manages thread access to shared resources.