Specify task order execution in Java

You can use PriorityBlockingQueue to specify Queue to ThreadPoolExecutor.

public class PriorityExecutor extends ThreadPoolExecutor {    public PriorityExecutor(int corePoolSize, int maximumPoolSize,            long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {        super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);    }    //Utitlity method to create thread pool easily    public static ExecutorService newFixedThreadPool(int nThreads) {        return new PriorityExecutor(nThreads, nThreads, 0L,                TimeUnit.MILLISECONDS, new PriorityBlockingQueue<Runnable>());    }    //Submit with New comparable task     public Future<?> submit(Runnable task, int priority) {        return super.submit(new ComparableFutureTask(task, null, priority));    }    //execute with New comparable task     public void execute(Runnable command, int priority) {        super.execute(new ComparableFutureTask(command, null, priority));    }}

Define ComparableFutureTask to compare on Priority.

class ComparableFutureTask<T> extends FutureTask<T>        implements            Comparable<ComparableFutureTask<T>> {    volatile int priority = 0;    public ComparableFutureTask(Runnable runnable, T result, int priority) {        super(runnable, result);        this.priority = priority;    }    public ComparableFutureTask(Callable<T> callable, int priority) {        super(callable);        this.priority = priority;    }    @Override    public int compareTo(ComparableFutureTask<T> o) {        return Integer.valueOf(priority).compareTo(o.priority);    }  }

ThreadPoolExecutor constructor accepts BlockingQueue.You can pass queue as PriorityBlockingQueue. It does not make any grantee on ordering you need to pass custom comparators to maintain order.

static BlockingQueue<Task> queue=new PriorityBlockingQueue<Task>(MAXPOOL,new TaskComparator());static ThreadPoolExecutor threadpool = new ThreadPoolExecutor(30, MAXPOOL,         MAXPOOL, TimeUnit.SECONDS, (PriorityBlockingQueue) queue, new mThreadFactory());class TaskComparator implements Comparator<Task>{  public int compare(Task t1, Task t2){    //write you own logic to compare two task.  }}