How do data exchanges and interactions occur between threads in a multithreaded application?

In a multithreaded Java application, data exchange and interaction between threads occur through shared objects and synchronization mechanisms. The main methods are:

• Shared variables and objects: Threads can read and modify shared data, but synchronization is used to prevent race conditions.
• The synchronized keyword: Allows locking access to a critical section of code so that only one thread can execute it.
• Classes from the java.util.concurrent package: For example, Lock, Semaphore, CountDownLatch, CyclicBarrier for more flexible synchronization.
• Interaction through queues: Threads can exchange data via thread-safe queues, such as BlockingQueue.
• Methods wait(), notify(), notifyAll(): Allow threads to wait for a certain condition and notify each other of changes.

Example of using synchronized and wait/notify:

class SharedResource {
    private int data;
    private boolean available = false;

    public synchronized void produce(int value) throws InterruptedException {
        while (available) {
            wait();
        }
        data = value;
        available = true;
        notify();
    }

    public synchronized int consume() throws InterruptedException {
        while (!available) {
            wait();
        }
        available = false;
        notify();
        return data;
    }
}

Thus, interaction is built on controlling access to shared data and notifying threads about events.