Stream is a convenient API which is introduced in Java 8 for aggregating values of aggregates such as arrays and collections.
In this article, I would like to introduce basic knowledge of Stream.
filter() returns some elements of this stream that match the given predicate.
List<String> sampleList = Arrays.asList("a1", "a2", "b1", "c2", "c1");
count() method in stream API counts the elements in stream object.
articles.stream().filter(i -> i.isDraft()).count() //=> n
noneMatch() method is a method which takes argument as a Predicate and if none of element of stream matches the given Predicate, then it returns true otherwise false.
articles.stream().noneMatch(i -> i.isDraft())
Instream.range(int startInclusive, int endExclusive) returns a sequential ordered stream elements from startInclusive(inclusive) to endExclusive(exclusive) by an incremental step of 1.
java.util.Optional<T> class is a wrapper for a non-null value that may or may not contain a non-null value.
final Optional<Article> article = Articles.stream()
To get and use the value from
Optional, write it as follows:
article.ifPresent(value -> System.out.println("Article.id is" + article.getId()));
ifPresent(Consumer<? super T> action) method from the Optional class takes an action on the value contained in Optional object.
In this section, I would like to introduce how to add an original validation.
Initially, please create an annotation class:
Please add validation class:
Please define a validation message in Unicode.
native2ascii command can convert UTF-8 to Unicode or ASCII.
You should add a converted sentence to
You can apply your original validator to your code:
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