Question

(Advanced Optional Sections) Fill in the blanks in each of the following statements: a) Method \(\quad\) of class Condition moves a single thread in an object's waiting state to the runnable state. b) Method \(\quad\) of class Condition moves every thread in an object's waiting state to the runnable state. c) \(A\) thread can call method \(\quad\) on a Condition object to release the associated Lock and place that thread in the ___ state. d) Class \(\quad\) implements the BlockingQueue interface using an array. e) Class Instant's static method ___ gets the current time. f) Duration method ___ returns the Duration as a long value milliseconds. g) NumberFormat static method ___ returns a NumberFormat that's used to format a number as a percentage. h) NumberFormat method __ returns a String representation of its argument in the specified numeric format. i) Arrays static method ___ fills an array with values produced by a generator function. j) Arrays static method \(\quad\) applies a BinaryOperator to the current and previous array elements and stores the result in the current element. k) To obtain a parallel stream, simply invoke method \(\quad\) on an existing stream. l) Among its many features a CompletableFuture enables you to asynchronously execute ___ that perform tasks or __ that return values.

Short answer

a) signal, b) signalAll, c) await, waiting, d) ArrayBlockingQueue, e) now, f) toMillis, g) getPercentInstance, h) format, i) setAll, j) parallelPrefix, k) parallel, l) Runnable, Callable

Step-by-step solution

Identify Method for Condition Class (a)

The method of class Condition that moves a single thread from the waiting state to the runnable state is 'signal'.

Identify Method for Condition Class (b)

The method of class Condition that moves every thread from the waiting state to the runnable state is 'signalAll'.

Identify Method and State for Threads (c)

A thread can call method 'await' on a Condition object to release the associated Lock and place that thread in the waiting state.

Identify Class Implementing Interface (d)

The class that implements the BlockingQueue interface using an array is 'ArrayBlockingQueue'.

Find Static Method of Class Instant (e)

Class Instant's static method that gets the current time is 'now'.

Discover Duration Method (f)

The Duration method that returns the Duration as a long value in milliseconds is 'toMillis'.

NumberFormat Static Method (g)

The NumberFormat static method that returns a NumberFormat for formatting a number as a percentage is 'getPercentInstance'.

NumberFormat Method for Formatting (h)

The NumberFormat method that returns a String representation of its argument in the specified numeric format is 'format'.

Find Arrays Static Method for Generation (i)

The Arrays static method that fills an array with values produced by a generator function is 'setAll'.

Identify Arrays Static Method for Binary Operations (j)

The Arrays static method that applies a BinaryOperator to the current and previous array elements and stores the result in the current element is 'parallelPrefix'.

Obtain a Parallel Stream (k)

To obtain a parallel stream, simply invoke method 'parallel' on an existing stream.

Understanding CompletableFuture Features (l)

A CompletableFuture enables you to asynchronously execute 'Runnable' that perform tasks or 'Callable' that return values.

Key concepts

Condition class in Java

In Java, the Condition class plays an essential role in multithreading, particularly when it comes to thread communication and synchronization. It provides a means for one thread to suspend execution (to 'await') until notified by another thread that some state condition may now be true.

Using the 'await' method, a thread can voluntarily relinquish the lock it holds on a particular object, entering a waiting state until another thread calls 'signal' to wake up one waiting thread, or 'signalAll' to wake up all waiting threads. This provides far more flexible control compared to the basic wait-and-notify mechanism of Object class, as it allows using multiple wait sets per lock, each represented by a different Condition object.

For example, in a producer-consumer scenario, a Condition could be used by the consumer to 'await' until the queue has items before proceeding to consume, ensuring that it only runs when relevant, thus improving the efficiency of thread use.

BlockingQueue interface

The BlockingQueue interface represents a thread-safe queue that is used to manage concurrent data access between threads. It supports operations that wait for the queue to become non-empty when retrieving an element and wait for space to become available in the queue when storing an element.

Classes implementing BlockingQueue, such as 'ArrayBlockingQueue', provide mechanisms to safely add or remove elements in a multithreaded environment. For instance, a producer thread can 'put' items in the queue, and if the queue is full, the thread is blocked until space is available. Conversely, a consumer thread can 'take' items, and it will be blocked if the queue is empty until an item becomes available.

Thus, the BlockingQueue is crucial for implementing producer-consumer patterns efficiently, where producers and consumers run concurrently, but must often wait for each other to proceed.

Java parallel streams

Java parallel streams are a pinnacle feature introduced to simplify writing concurrent code. They allow for processing elements of a collection in parallel, utilizing multiple cores of a CPU, which can lead to significant performance improvements.

To create a parallel stream, you simply call the 'parallel()' method on an existing stream. The elements of the stream are then divided into multiple chunks that are processed independently and potentially simultaneously on separate cores. After the processing is complete, the results are merged back into a single stream.

Parallel streams can be remarkably effective for computational intensive operations or large collections. However, it's crucial to remember that not every operation is automatically faster with parallel streams. The overhead of coordinating threads, splitting the data, and merging results can sometimes outweigh the benefits, so it's important to use them judiciously.

CompletableFuture in Java

CompletableFuture is an enhancement to Java's Future interface that can be explicitly completed, can chain multiple asynchronous operations, and combine them in a non-blocking way. It offers a wealth of methods that facilitate error handling, asynchronous callbacks, and combining several asynchronous tasks into a single computational unit.

With CompletableFuture, you can perform asynchronous operations by defining 'Runnable' tasks, which don't return a value, or 'Callable' tasks, which do return a value. You can then chain these tasks with methods like 'thenApply', 'thenAccept', and 'thenRun' for post-completion activities, making it easier to write non-blocking, asynchronous, and event-driven programs.

CompletableFuture is a powerful tool that can make multi-threaded programs more responsive by ensuring that long-running tasks do not block the main application thread, enabling the app to continue doing useful work while waiting for the long-running tasks to complete.