title: Java: How to make this main thread wait for the new thread to terminate
body: <p>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 main thread from getting blocked.  However, a little later on I need to wait for the output thread to complete/terminate before going on, and I'm not sure how to do that.  I think that join() is the usual way to do this but I'm not sure how to do that in this case.  Here is the relevant part of the java code.</p>
  
  <pre><code>    // Capture output from process called child on a separate thread
  
      final StringBuffer outtext = new StringBuffer("");
      new Thread(new Runnable() {
          public void run() {
              InputStream in = null;
              in = child.getInputStream();
              try {
                  if (in != null) {
                      BufferedReader reader = new BufferedReader(new InputStreamReader(in));
                      String line = reader.readLine();
                      while ((line != null)) {
                          outtext.append(line).append("\n");
                          ServerFile.appendUserOpTextFile(userName, opname, outfile, line+"\n");
                          line = reader.readLine();
                      }
                  }
              } catch (IOException iox) {
                  throw new RuntimeException(iox);
              }
          }
      }).start();
  
      // Write input to for the child process on this main thread
      //
      String intext = ServerFile.readUserOpTextFile(userName, opname, infile);
      OutputStream out = child.getOutputStream();
      try {
          out.write(intext.getBytes());
          out.close();
      } catch (IOException iox) {
          throw new RuntimeException(iox);
      }
  
      //  ***HERE IS WHERE I NEED TO WAIT FOR THE THREAD TO FINISH ***
  
      // Other code goes here that needs to wait for outtext to get all
      // of the output from the process
  
      // Then, finally, when all the remaining code is finished, I return
      // the contents of outtext
  
      return outtext.toString();
  </code></pre>