Forkjoin and optional framework in Java 8

Parallel stream and serial stream

Parallel flow is to divide a content into multiple data blocks and process each data block with different threads.

Java 8 optimizes parallelism, and we can easily operate data in parallel. The stream API can declaratively switch between parallel and sequential streams through parallel() and sequential().

Understanding the fork / join framework

Fork / join framework: when necessary, fork a large task into several small tasks (when it cannot be disassembled), and then join and summarize the running results of small tasks.

The difference between fork / join framework and traditional thread pool:

Adopt "work stealing" mode:

When executing a new task, it can split it into smaller tasks, add the small task to the thread queue, and then steal one from the queue of a random thread and put it in its own queue.

Compared with the common thread pool implementation, the advantage of fork / join framework lies in the processing of the tasks contained in it In a general thread pool, if a thread cannot continue to run for some reason, the thread will be in a waiting state In the fork / join framework implementation, if a subproblem cannot continue to run because it waits for another subproblem to complete Then the thread dealing with this sub problem will actively look for other sub problems that have not yet run to execute This method reduces the waiting time of threads and improves performance.

Optional class

The optional < T > class (Java. Util. Optional) is a container class that represents the presence or absence of a value.

Originally, null was used to indicate that a value does not exist. Now optional can better express this concept. And you can avoid null pointer exceptions.

Common methods:

Optional. Of (T): create an optional instance

Optional. Empty(): create an empty optional instance

Optional. Ofnullable (T): if t is not null, create an optional instance; otherwise, create an empty instance

Ispresent(): judge whether the value is included

Orelse (T): if the calling object contains a value, return the value; otherwise, return t

Orelseget (supplier s): if the calling object contains a value, return the value; otherwise, return the value obtained by S

Map (function f): if there is a value, process it and return the processed optional. Otherwise, return optional empty()

Flatmap (function mapper): similar to map, the return value must be optional

The above is all about the experience of using forkjoin and optional framework in java8. If you don't understand anything during your study, you can discuss it in the message area below.