Java: How to make this main thread wait for the new thread to terminate

Question

I have a java class that creates a process, called child, using ProcessBuilder. The child process generates a lot of output that I am draining on a separate thread to keep the

Answer 1

You can join on that thread. You would get the instance of the thread and when needed to wait invoke its join method.

 Thread th = new Thread(new Runnable() {  ... } );
 th.start();
 //do work 
 //when need to wait for it to finish
 th.join();
 //th has now finished

Others will suggest a CountdownLatch, CyclicBarrier or even a Future but I find this to be easiest to implement on a very low level.

Answer 2

final StringBuffer outtext = new StringBuffer("");  
Thread outputDrainThread = new Thread(new Runnable() {
    public void run() {
        // ... 
    }
}).start();

// ...

//  ***HERE IS WHERE I NEED TO WAIT FOR THE THREAD TO FINISH ***
outputDrainThread.join();    

// ...
return outtext.toString();

Answer 3

You have to assign your thread to a variable and later call join() on this variable.