Filtering Data with Java 8 Streams API

Internal

• Java 8 Streams API

Overview

Filtering in this context means dropping certain elements based on a criterion.

All filtering methods are intermediate operations.

Methods

filter()

The most generic way to filter data in a stream is to apply a criterion, in form of a predicate. The filtering behavior is passed as a lambda expression predicate to the filter() method. The predicate will allow or exclude elements from the stream.

Stream<T> filter(Predicate<? super T> predicate);

distinct()

The Stream interface also exposes a distinct() method that filters out duplicates, retaining only the unique elements:

Stream<T> distinct();

The comparison is performed using the equals() method applied to the object flowing through the stream.

distinct() is a stateful unbounded operation.

Discarding Leading Elements Based on the Evaluation of a Predicate

Stream<T> dropWhile​(Predicate<? super T> predicate);

Introduced in Java 9. To process: https://docs.oracle.com/javase/10/docs/api/java/util/stream/Stream.html#dropWhile(java.util.function.Predicate)

Discarding First n Elements

Stream<T> skip​(long n);

skip() is a stateful bounded operation.

Discarding Trailing Elements Based on the Evaluation of a Predicate

Stream<T> takeWhile​(Predicate<? super T> predicate);

Introduced in Java 9. To process: https://docs.oracle.com/javase/10/docs/api/java/util/stream/Stream.html#takeWhile(java.util.function.Predicate)

Truncating the Stream

Truncate the stream to contain no more than the given number of elements.

Stream<T> limit(long maxSize);