{"id":6847,"date":"2019-04-06T10:31:19","date_gmt":"2019-04-06T10:31:19","guid":{"rendered":"http:\/\/putridparrot.com\/blog\/?p=6847"},"modified":"2019-04-06T10:31:19","modified_gmt":"2019-04-06T10:31:19","slug":"javas-linq-equivalent-streams","status":"publish","type":"post","link":"https:\/\/putridparrot.com\/blog\/javas-linq-equivalent-streams\/","title":{"rendered":"Java’s Linq equivalent, Streams"},"content":{"rendered":"

I was working on a previous post on Java and GraphQL and wanted to use a Linq query. Java doesn’t have Linq but it does have something equivalent (in Java 8) called Stream. For the examples within this post we’ll create the following simple method for generating our test data<\/p>\n

\r\nprivate static List<String> getData() {\r\n   return Arrays.asList(\r\n      "2", "2", "2", "4", "4", \r\n      "6", "7", "7", "9", "10");\r\n}\r\n<\/pre>\n
Let’s look at some of the standard sort of functionality…<\/p>\n
Distinct<\/strong><\/p>\n
We can get a distinct stream from our data using<\/p>\n
\r\nStream<String> distinct = getData()\r\n   .stream()\r\n   .distinct();\r\n<\/pre>\n
Selection\/Filtering<\/strong><\/p>\n
If we want to filter our data to select only strings longer than one character, for example, then we can use the following<\/p>\n
\r\nStream<String> where = getData()\r\n   .stream()\r\n   .filter(s -> s.length() > 1);\r\n<\/pre>\n
Matching<\/strong><\/p>\n
There are several methods which return a Boolean, for example if all items in the Stream are of a certain value, or any of the values no matches, for example<\/p>\n
\r\nboolean allMatch = getData()\r\n   .stream()\r\n   .allMatch(s -> s.contains("4"));\r\n\r\nboolean anyMatch = getData()\r\n   .stream()\r\n   .anyMatch(s -> s.contains("4"));\r\n\r\nboolean noneMatch = getData()\r\n   .stream()\r\n   .noneMatch(s -> s.contains("4"));\r\n<\/pre>\n
Map<\/strong><\/p>\n
In scenarios where we wish to change the data returned from a stream (i.e. like Select in Linq), for example we’ll simply loop through each item and return the length of each string as a Stream, we can use <\/p>\n
\r\nStream<Integer> select = getData()\r\n   .stream()\r\n   .map(String::length);\r\n<\/pre>\n
Reduce<\/strong><\/p>\n
If we want to take a stream and reduce it to a single value, for example taking our data and concatenating into a single String, we could use the following <\/p>\n
\r\nString reduce = getData()\r\n   .stream()\r\n   .reduce("", (a, b) -> a + b);\r\n<\/pre>\n
The initial value “” in this case is a starting value for the reduced value, in this case we’re not wanting to prepend anything to our string. The result of the reduce is a String with the value 22244677910.<\/p>\n
Creating an empty Stream<\/strong><\/p>\n
We can create an empty Stream (useful in those situations where we do not wish to return a null) using<\/p>\n
\r\nStream<String> empty = Stream.empty();\r\n<\/pre>\n
Iteration<\/strong><\/p>\n
We can iterate over the Stream using the forEach method, for example<\/p>\n
\r\ngetData()\r\n   .stream()\r\n   .forEach(s -> System.out.println(s));\r\n<\/pre>\n
Parallel Streams<\/strong><\/p>\n
We can also parallelize (is that a word) our Stream using the parallelStream<\/em>, for example<\/p>\n
\r\nStream<Integer> parallel = getData()\r\n   .parallelStream()\r\n   .map(String::length);\r\n<\/pre>\n
As you’d expect the order or processing of the map<\/em> in this instance is indeterminate.<\/p>\n
Obviously there’s more to Stream than I’ve listed here, but you get the idea.<\/p>\n","protected":false},"excerpt":{"rendered":"
I was working on a previous post on Java and GraphQL and wanted to use a Linq query. Java doesn’t have Linq but it does have something equivalent (in Java 8) called Stream. For the examples within this post we’ll create the following simple method for generating our test data private static List<String> getData() { […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[161],"tags":[],"class_list":["post-6847","post","type-post","status-publish","format-standard","hentry","category-java"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/6847","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/comments?post=6847"}],"version-history":[{"count":3,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/6847\/revisions"}],"predecessor-version":[{"id":6884,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/6847\/revisions\/6884"}],"wp:attachment":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/media?parent=6847"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/categories?post=6847"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/tags?post=6847"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}