multithreading - Doesn't executor service in java submits tasks parallelly? -

i playing java multithreading code. created executor service fixed thread pool. submitting 2 tasks sequentially. tried make first task long thread.sleep. thinking these 2 tasks run parallelly. however, when run program, programs waits sometime, prints b, means compiler finished first task @ first before going second task. actually, expecting, second task short task, complete before first task. explanation please?

 public static void main(string[] args) {     executorservice executor = executors.newfixedthreadpool(10);     map<string, string> map = new hashmap<>();     readwritelock lock = new reentrantreadwritelock();     executor.submit(() -> {         lock.writelock().lock();         try {             thread.sleep(10000);             map.put("boo", "mar");             system.out.println("a");         } catch (interruptedexception e) {             // todo auto-generated catch block             e.printstacktrace();         } {             lock.writelock().unlock();         }     });      executor.submit(() -> {         lock.writelock().lock();         try {             thread.sleep(1);             map.put("foo", "bar");             system.out.println("b");         } catch (interruptedexception e) {             // todo auto-generated catch block             e.printstacktrace();         } {             lock.writelock().unlock();         }     });      executor.shutdown(); } 

you "locking" writelock before first thread sleeps.. lock locked 10 seconds.. unlocked. second thread waiting 10 seconds acquire lock.

sequence of events:

thread 1: starts thread 2: starts  thread 1: acquire lock , wait 10 seconds. thread 2: try acquire lock (ends waiting 10 seconds because acquired thread 1).  thread 1: prints data. thread 1: unlocks lock.  thread 2: acquires lock. thread 2: prints data. thread 2: unlocks lock. 

try below (it acquires lock when necessary.. ie: when doing write operation or modification of map):

public static void main(string[] args) {         executorservice executor = executors.newfixedthreadpool(10);         map<string, string> map = new hashmap<>();         readwritelock lock = new reentrantreadwritelock();         executor.submit(() -> {             try {                 thread.sleep(10000);                  lock.writelock().lock();                 map.put("boo", "mar");                 lock.writelock().unlock();                  system.out.println("a");             } catch (interruptedexception e) {                 e.printstacktrace();             }         });          executor.submit(() -> {             try {                 thread.sleep(1);                  lock.writelock().lock();                 map.put("foo", "bar");                 lock.writelock().unlock();                  system.out.println("b");             } catch (interruptedexception e) {                 e.printstacktrace();             }         });          executor.shutdown();     }