Thread lifecycle:

 The Thread lifecycle describes the various states that a thread can go through during its lifetime. Understanding the Thread lifecycle is essential for managing threads effectively.


The Thread lifecycle consists of the following states:


New: The thread is in the new state when it is created but has not yet started its execution. In this state, the thread has been instantiated, but the start() method has not been called.


Runnable: The thread enters the runnable state after the start() method is invoked. In this state, the thread is eligible to run, and the operating system's thread scheduler decides when to allocate CPU time to the thread. However, it does not guarantee immediate execution; it depends on the scheduling algorithm and the availability of system resources.


Running: The thread enters the running state when the scheduler selects it for execution. In this state, the thread's code is being executed.


Blocked/Waiting: A thread can enter the blocked or waiting state for various reasons. For example:


Blocked: A thread can be blocked when it is waiting for a monitor lock to be released by another thread. This can happen when a synchronized block or method is being executed by another thread.

Waiting: A thread can go into a waiting state by explicitly calling methods like wait(), sleep(), or join(), or by waiting for a signal from another thread using mechanisms like wait()/notify() or Condition objects.

When a thread is blocked or waiting, it is temporarily inactive and does not consume CPU time until it transitions back to the runnable state.


Terminated: The thread enters the terminated state when its run() method completes execution or when an uncaught exception occurs within the thread. Once a thread reaches this state, it cannot be started again.


Here's an example that demonstrates the Thread lifecycle:


public class ThreadLifecycleExample {
public static void main(String[] args) {
Thread thread = new Thread(() -> { 
 System.out.println("Thread is running."); 
try { 
 Thread.sleep(2000);
 } 
catch (InterruptedException e) {
 e.printStackTrace(); 
 }
 System.out.println("Thread has completed.");
 });
 System.out.println("Thread is in the new state."); 
 thread.start(); 
 System.out.println("Thread has started and is now in the runnable state.");
try { 
 Thread.sleep(500); 
 } 
catch (InterruptedException e) {
 e.printStackTrace();
 }
 System.out.println("Thread is currently running.");
try { 
 thread.join(); 
 } 
catch (InterruptedException e) { 
 e.printStackTrace();
 } 
 System.out.println("Thread has terminated.");
    }
 }

In this example, we create a new thread using the Thread constructor and provide a Runnable lambda expression. 

After starting the thread, it enters the runnable state. 

The Thread.sleep() method simulates some processing time within the thread.

After the sleep, the thread completes its execution and enters the terminated state.


The output of the example will be:


Thread is in the new state. 
Thread has started and is now in the runnable state.

Thread is currently running.

Thread is running. 
Thread has completed.

Thread has terminated.

Understanding the different states of the Thread lifecycle is crucial for managing threads effectively, implementing synchronization mechanisms, and ensuring proper coordination between threads in concurrent programming scenarios.