Concurrency - Java: How to Program Early Objects - page 1041

Section 23.14 (Advanced) Interfaces Callable and Future
•The Callable (p. 1030) interface (of package java.util.concurrent ) declares a single method
named call that allows a task to return a value.
• ExecutorService method submit (p. 1030) executes a Callable passed in as its argument. Meth-
od submit returns an object of type Future (of package java.util.concurrent ) that represents
the future result of the executing Callable .
• Interface Future (p. 1030) declares method get to return the result of the Callable . The inter-
face also provides methods that enable you to cancel a Callable 's execution, determine whether
the Callable was cancelled and determine whether the Callable completed its task.
• Java SE 8 introduces a new CompletableFuture class (package java.util.concurrent ; p. 1030),
which implements the Future interface and enables you to asynchronously execute Runnable s
that perform tasks or Supplier s that return values.
• Interface Supplier (p. 1030), like interface Callable , is a functional interface with a single meth-
od (in this case, get ) that receives no arguments and returns a result.
• CompletableFuture static method supplyAsync (p. 1033) asynchronously executes a Supplier
task that returns a value.
• CompletableFuture static method runAsync (p. 1034) asynchronously executes a Runnable task
that does not return a result.
• CompletableFuture method get is a blocking method—it causes the calling thread to wait until
the asynchronous task completes and returns its results.

Section 23.15 (Advanced) Fork/Join Framework
• Java's concurrency APIs include the fork/join framework, which helps programmers parallelize
algorithms. The fork/join framework particularly well suited to divide-and-conquer-style algo-
rithms, like the merge sort.

Self-Review Exercises
23.1

Fill in the blanks in each of the following statements:
a) A thread enters the terminated state when .
b) To pause for a designated number of milliseconds and resume execution, a thread
should call method of class .
c) A runnable thread can enter the state for a specified interval of time.
d) At the operating-system level, the runnable state actually encompasses two separate
states, and .
e) Runnable s are executed using a class that implements the interface.
f) ExecutorService method ends each thread in an ExecutorService as soon as
it finishes executing its current Runnable , if any.

g) In a(n) relationship, the generates data and stores it in a shared ob-

ject, and the reads data from the shared object.

h) Keyword indicates that only one thread at a time should execute on an object.

23.2 (Advanced Optional Sections) Fill in the blanks in each of the following statements:

a) Method of class Condition moves a single thread in an object's waiting state

to the runnable state.

b) Method of class Condition moves every thread in an object's waiting state to

the runnable state.

c) A thread can call method on a Condition object to release the associated Lock

and place that thread in the state.