Java - Threads

Java Threads are a fundamental aspect of concurrent programming in Java. A thread is a lightweight sub-process that runs in parallel with the main program, allowing multiple tasks to be performed simultaneously.

In Java, threads can be created and managed using the java.lang.Thread class. Each thread is associated with an instance of the Thread class, and can be started, stopped, and joined with other threads as needed.

Here are some important concepts related to Java threads:

• Thread States: A thread can be in one of several states at any given time, including new, runnable, blocked, waiting, and terminated.
• Synchronization: Synchronization is the process of controlling access to shared resources by multiple threads. In Java, synchronization can be achieved using the synchronized keyword and the wait(), notify(), and notifyAll() methods.
• Thread Pools: A thread pool is a group of threads that can be used to execute tasks in parallel. Java provides built-in support for thread pools through the java.util.concurrent.Executor framework.
• Thread Safety: Thread safety is the property of a program or system that ensures correct behavior in the presence of multiple threads. Thread safety can be achieved through proper synchronization and other techniques.

To use Java threads, you must first create a new instance of the Thread class, passing in a reference to the code that you want to execute in the new thread. You can then start the thread using the start() method, which causes the run() method of the thread to be executed in a separate thread of execution.

class MyThread extends Thread {
   public void run() {
      System.out.println("Hello from MyThread!");
   }
}

public class Main {
   public static void main(String[] args) {
      MyThread thread = new MyThread();
      thread.start();
   }
}

This will create a new thread that outputs "Hello from MyThread!" to the console when it is started.

Java threads can be used to perform a wide range of tasks, including background processing, network communication, and user interface updates. By understanding the concepts of thread states, synchronization, thread pools, and thread safety, you can create more efficient and robust Java applications.

Thread Priority:

Thread priority is an important aspect of Java threads that allows you to set the relative importance of a thread to the JVM. Higher-priority threads are executed before lower-priority threads. Here's an example of setting the priority of a thread:

Thread thread = new Thread();
thread.setPriority(Thread.MAX_PRIORITY);

Synchronization:

Synchronization is a mechanism that allows multiple threads to access shared resources in a coordinated and safe manner. Here's an example of using the synchronized keyword to synchronize a method:

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

Thread Groups:

A thread group is a collection of threads that can be manipulated as a single entity. Thread groups provide a way to organize threads and set properties that affect all threads in the group. Here's an example of creating a thread group:

ThreadGroup group = new ThreadGroup("MyThreadGroup");

Thread Interruption:

Thread interruption is a mechanism that allows one thread to request the interruption of another thread. The target thread is not forced to stop, but is given the opportunity to stop gracefully. Here's an example of interrupting a thread:

Thread thread = new Thread(() -> {
    while(!Thread.interrupted()) {
        // Do some work...
    }
});
thread.start();
thread.interrupt();

Thread Local Variables:

Thread local variables are variables that are local to a specific thread. Each thread has its own copy of the variable, so changes made by one thread do not affect other threads. Here's an example of using a thread local variable:

ThreadLocal<Integer> threadLocal = new ThreadLocal<>();
threadLocal.set(42);
int value = threadLocal.get();