isAlive( ) and join( ) methods in Thread of java

In Java, the isAlive() and join() methods are part of the Thread class and are used to manage the execution and synchronization of threads.

isAlive() Method:

The isAlive() method is used to determine whether a thread is still alive or has terminated. A thread is considered alive if it has been started and has not yet terminated.

Thread myThread = new Thread(() -> {
    // Thread logic
});

myThread.start(); // Start the thread

if (myThread.isAlive()) {
    System.out.println("Thread is still alive");
} else {
    System.out.println("Thread has terminated");
}

join() Method:

The join() method is used to wait for a thread to complete its execution. When a thread calls join() on another thread, it will wait until that other thread finishes before continuing its own execution.

Thread thread1 = new Thread(() -> {
    // Thread 1 logic
});

Thread thread2 = new Thread(() -> {
    // Thread 2 logic
});

thread1.start();
thread2.start();

try {
    thread1.join(); // Wait for thread1 to finish
    System.out.println("Thread 1 has finished");

    thread2.join(); // Wait for thread2 to finish
    System.out.println("Thread 2 has finished");
} catch (InterruptedException e) {
    e.printStackTrace();
}

In the example above, the main thread waits for thread1 to finish using thread1.join(), and then it waits for thread2 to finish using thread2.join().

Using join() with Timeout:

The join() method also has an overloaded version that allows you to specify a timeout period. If the specified timeout period elapses before the thread terminates, the join() method returns.

try {
    thread1.join(5000); // Wait for at most 5 seconds for thread1 to finish
} catch (InterruptedException e) {
    e.printStackTrace();
}

Benefits of join():

1. Sequential Execution:

• join() can be used to ensure that threads execute in a specific order, creating a form of sequential execution.

1. Synchronization:

• It helps in synchronizing the activities of multiple threads, making it easier to coordinate their execution.

1. Wait for Completion:

• It allows one thread to wait for the completion of another thread before proceeding.

Considerations:

1. Deadlock:

• Care must be taken to avoid potential deadlock situations when using join(). For example, if one thread is waiting for another, and the second thread is waiting for the first, a deadlock can occur.

1. InterruptedException:

• Both isAlive() and join() methods can throw InterruptedException, and proper exception handling is recommended.

1. Timeouts:

• When using join() with a timeout, consider the implications of the timeout value on the overall program behavior.

1. Thread Termination:

• The use of isAlive() is often used to check if a thread has terminated, but it’s essential to understand that the thread status can change between the call to isAlive() and the subsequent actions.

In summary, isAlive() helps determine the current status of a thread, and join() is a powerful mechanism for coordinating the execution of multiple threads. When used judiciously, they contribute to the effective management of concurrent threads in Java programs.

There are two method in java for Thread to determine whether a thread has finished. One is isAlive( ) method and another is join( ) method

isAlive( )

The isAlive( ) method returns true if the thread upon which it is called is still running. It returns false otherwise

General form

final boolean isAlive( )

join( )

This method waits until the thread on which it is called terminates. Its name comes from the concept of the calling thread waiting until the specified thread joins it. Additional forms of join( ) allow you to specify a maximum amount of time that you want to wait for the specified thread to terminate

final void join( ) throws InterruptedException

Example of isAlive() and join()

class NewThread implements Runnable {
String name; // name of thread
Thread t;
NewThread(String threadname) {
name = threadname;
t = new Thread(this, name);
System.out.println("New thread: " + t);
t.start(); // Start the thread
}
// This is the entry point for thread.
public void run() {
try {
for(int i = 5; i > 0; i--) {
System.out.println(name + ": " + i);
Thread.sleep(1000);
}
} catch (InterruptedException e) {
System.out.println(name + " interrupted.");
}
System.out.println(name + " exiting.");
}
}
class DemoJoin {
public static void main(String args[]) {
NewThread ob1 = new NewThread("One");
NewThread ob2 = new NewThread("Two");
NewThread ob3 = new NewThread("Three");
System.out.println("Thread One is alive: "
+ ob1.t.isAlive());
System.out.println("Thread Two is alive: "
+ ob2.t.isAlive());
System.out.println("Thread Three is alive: "
+ ob3.t.isAlive());
// wait for threads to finish
try {
System.out.println("Waiting for threads to finish.");
ob1.t.join();
ob2.t.join();
ob3.t.join();
} catch (InterruptedException e) {
System.out.println("Main thread Interrupted");
}
System.out.println("Thread One is alive: "
+ ob1.t.isAlive());
System.out.println("Thread Two is alive: "
+ ob2.t.isAlive());
System.out.println("Thread Three is alive: "
+ ob3.t.isAlive());
System.out.println("Main thread exiting.");
}
}

Output

New thread: Thread[One,5,main]
New thread: Thread[Two,5,main]
New thread: Thread[Three,5,main]
Thread One is alive: true
Thread Two is alive: true
Thread Three is alive: true
Waiting for threads to finish.
One: 5
Two: 5
Three: 5
One: 4
Two: 4
Three: 4
One: 3
Two: 3
Three: 3
One: 2
Two: 2
Three: 2

One: 1
Two: 1
Three: 1
Two exiting.
Three exiting.
One exiting.
Thread One is alive: false
Thread Two is alive: false
Thread Three is alive: false
Main thread exiting.