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.
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. 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.
Here is an improved version of the preceding example that uses join( ) to ensure that the
main thread is the last to stop. It also demonstrates the isAlive( ) method.
// Using join() to wait for threads to finish.
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");
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