Using For loop with Multi-threading in Java 1.6

Question

I'm trying to use For loop with multi-threading in Java 1.6. I tried to use streams but apparently it was added in Java 1.8, so i tried to useExecutorService and Future but i can't make it work.

What i want is just make this code multi-threaded with fixed number of threads.

for (ExampleType ex : exampleData) {
    exampleFunction(ex.getSomeData());
}

What i tried and didn't work, found it somewhere from google

final ExecutorService testExecutor = Executors.newFixedThreadPool(10); // just 10 thread
final List<Future<?>> executeDatas = new ArrayList<List>();

for (ExampleType ex : exampleData) {
    Future<?> executeData = testExecutor.submit(() -> {
        exampleFunction(ex.getSomeData());
    });
    executeDatas.add(executeData);
}

for (Future<?> executeData : executeDatas) {
    executeData.done(); // do i need to write stuff here? i don't have done() function
}

It probably would've worked but says diamond operator is not supported in -source 1.6. Yeah i'm not sure how to handle from here and been stuck. Any help is appreciated

That code won't work in Java 6 because of the lambda. You'd need to write it an anonymous class. — Andy Turner
– Andy Turner, Commented Apr 26, 2018 at 18:34
executeData.get(); to wait for the results in the order you submitted them. If you want them in completion order, use a CompletionService. — Andy Turner
– Andy Turner, Commented Apr 26, 2018 at 18:35

Roman Puchkovskiy · Accepted Answer · 2018-04-26 19:05:15Z

3

For some reason, noone shows the transformed code, so I'll do it:

final ExecutorService testExecutor = Executors.newFixedThreadPool(10);
final List<Future<?>> executeDatas = new ArrayList<Future<?>>();

for (ExampleType ex : exampleData) {
    Future<?> executeData = testExecutor.submit(new Runnable() {
        @Override
        public void run() {
            exampleFunction(ex.getSomeData());
        }
    });
    executeDatas.add(executeData);
}

for (Future<?> executeData : executeDatas) {
    // calling get in loop to effectively wait for all the futures to finish
    executeData.get();
}

Three changes are made:

ArrayList<List> replaced with with ArrayList<Future<?>>
Lambda replaced with anonymous class instantiation
.done() changed to .get() to wait for all the futures to finish execution

answered Apr 26, 2018 at 19:05

Roman Puchkovskiy

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