Java parallel stream用法

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先摘錄關於collection並發的一段話：

One difficulty in implementing parallelism in applications that use collections is that collections are not thread-safe, which means that multiple threads cannot manipulate a collection without introducing thread interference or memory consistency errors. The Collections Framework provides synchronization wrappers, which add automatic synchronization to an arbitrary collection, making it thread-safe. However, synchronization introduces thread contention. You want to avoid thread contention because it prevents threads from running in parallel. Aggregate operations and parallel streams enable you to implement parallelism with non-thread-safe collections provided that you do not modify the collection while you are operating on it.

這段話能夠說明為什麼需要parallel stream.

下面看看如何使用parallel stream,有兩種調用方式：

1.

double average = roster    .parallelStream()    .filter(p -> p.getGender() == Person.Sex.MALE)    .mapToInt(Person::getAge)    .average()    .getAsDouble();

　　

2.

double average = roster    .stream().parallel()    .filter(p -> p.getGender() == Person.Sex.MALE)    .mapToInt(Person::getAge)    .average()    .getAsDouble();

　　

還有個關於排序的問題，下面這段代碼使用forEachOrdered是能保證順序的，用一般的forEach是無法保證順序的：

listOfIntegers    .parallelStream()    .forEachOrdered(e -> System.out.print(e + " "));

　　

Java parallel stream用法