Using isAlive( ) and join( )
1.isAlive()
Two ways exist to determine whether a thread has finished. First, you can call isAlive( ) on the thread. This method is defined by Thread, and its general form is shown here:
final boolean isAlive( )
The isAlive( ) method returns true if the thread upon which it is called is still running. It returns false otherwise.
class first implements Runnable {
Thread t;
first(String name) {
t = new Thread(this, name);
t.start();
}
public void run() {
System.out.println("T" + t);
}
}
public class IsAliveExample {
public static void main(String[] args) {
System.out.println("Main thread is alive " +
Thread.currentThread().isAlive());
Thread t1 = new Thread(new first("First Thread"));
System.out.println("is t1 alive " + t1.isAlive()); // executed and
// closed in above
// line
Thread t2 = new Thread(new first("Second Thread"));
}
}
2.join
While isAlive( ) is occasionally useful, the method that you will more commonly use to wait for a thread to finish is called join( ), shown here:
final void join( ) throws InterruptedException
This method waits until the thread on which it is called terminates.Example is as follows :
class Callme {
void call(String msg) {
System.out.print("Start " + msg);
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
System.out.println("Interrupted");
}
System.out.println(" End");
}
}
class Caller implements Runnable {
String msg;
Callme target;
Thread t;
public Caller(Callme targ, String s) {
target = targ;
msg = s;
t = new Thread(this);
t.start();
}
public void run() {
synchronized (target) { // synchronized block
target.call(msg);
}
}
}
public class example5 {
public static void main(String args[]) {
Callme target = new Callme();
Caller ob1 = new Caller(target, "A");
Caller ob2 = new Caller(target, "B");
Caller ob3 = new Caller(target, "C");
// wait for threads to end
try {
System.out.println(ob1.t.isAlive());
ob1.t.join();
ob2.t.join();
ob3.t.join();
} catch (Exception e) {
System.out.println("Interrupted");
}
}
}
