Java Wait for thread to finish

Question

I have a thread downloading data and I want to wait until the download is finished before I load the data   Is there a standard way of doing this   More Info   I have a Download class that gets data from a URL  Serialized POJOs    Download is Runnable and Observable   It keeps track of the bytes downloaded and download size   I have a progress bar that displays the progress to the User    The GUI observes Download to update the progress bar   When the POJO is downloaded I want to get it and move to the next step   Each step has to wait for the previous to finish   The problem is I cant think of a way to pause my application to wait for the download thread   Once the download is finished I want to call download getObject   which will return the data as an object   I can then cast it and get on with the next download   I have a helper class that manages the URLs for download and makes all of the calls to Download   This call will call getObject and do the casting   The Gui calls helper getUser     helper starts the thread running and I want it to  know  when it is finished so it can return the casted object    Any suggestions examples   I am in the beginning stages of this design so I am willing to change it   Thank you kindly   Update   I followed http   download oracle com javase 6 docs api javax swing SwingWorker html get and used modal to block until the thread finished   The code was very messy and I don t like this approach   I will keep trying to find a  clean  way to handle the workflow of the download processes

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Generally  when you want to wait for a thread to finish  you should call join   on it

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The join   method allows one thread to wait for the completion of another However  as with sleep  join is dependent on the OS for timing  so you should not assume that join will wait exactly as long as you specify

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You can use join   to wait for all threads to finish  Keep all objects of threads in the global ArrayList at the time of creating threads  After that keep it in loop like below   for  int i   0  i  lt  10  i           Thread T1   new Thread new ThreadTest i                        T1 start                        arrThreads add T1       for  int i   0  i  lt  arrThreads size    i           arrThreads get i  join         Check here for complete details  http   www letmeknows com 2017 04 24 wait-for-threads-to-finish-java

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Any suggestions examples  I followed SwingWorker    The code was very messy and I don t like this approach    Instead of get    which waits for completion  use process   and setProgress   to show intermediate results  as suggested in this simple example or this related example

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You could use a CountDownLatch from the java util concurrent package  It is very useful when waiting for one or more threads to complete before continuing execution in the awaiting thread   For example  waiting for three tasks to complete   CountDownLatch latch   new CountDownLatch 3       latch await       Wait for countdown   The other thread s  then each call latch countDown   when complete with the their tasks  Once the countdown is complete  three in this example  the execution will continue

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I imagine that you re calling your download in a background thread such as provided by a SwingWorker  If so  then simply call your next code sequentially in the same SwingWorker s doInBackground method

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SwingWorker has doInBackground   which you can use to perform a task  You have the option to invoke get   and wait for the download to complete or you can override the done   method which will be invoked on the event dispatch thread once the SwingWorker completes   The Swingworker has advantages to your current approach in that it has many of the features you are looking for so there is no need to reinvent the wheel  You are able to use the getProgress   and setProgress   methods as an alternative to an observer on the runnable for download progress   The done   method as I stated above is called after the worker finishes executing and is performed on the EDT  this allows you load the data after the download has completed

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Thread has a method that does that for you join which will block until the thread has finished executing

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Better alternatives to join   method have been evolved over a period of time   ExecutorService html invokeAll is one alternative      Executes the given tasks  returning a list of Futures holding their status and results when all complete  Future isDone   is true for each element of the returned list     Note that a completed task could have terminated either normally or by throwing an exception  The results of this method are undefined if the given collection is modified while this operation is in progress   ForkJoinPool or Executors html newWorkStealingPool provides other alternatives to achieve the same purpose    Example code snippet    import java util concurrent     import java util     public class InvokeAllDemo      public InvokeAllDemo            System out println  creating service            ExecutorService service   Executors newFixedThreadPool Runtime getRuntime   availableProcessors              List lt MyCallable gt  futureList   new ArrayList lt MyCallable gt             for   int i 0  i lt 10  i                 MyCallable myCallable   new MyCallable  long i               futureList add myCallable                     System out println  Start            try              List lt Future lt Long gt  gt  futures   service invokeAll futureList              catch Exception err               err printStackTrace                      System out println  Completed            service shutdown              public static void main String args             InvokeAllDemo demo   new InvokeAllDemo              class MyCallable implements Callable lt Long gt           Long id   0L          public MyCallable Long val               this id   val                    public Long call                   Add your business logic             return id

[java] Java Wait for thread to finish

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