Stream api in java 8

API is an acronym for Application Programming Interface, which is software and the java streams work on a data source. Consider a stream like a flow of water in a small canal. Let’s take a real-life example. Each time a user uses an application that is popular these days like WhatsApp in order to communicate via delivering text messages or calls to other users. Both users are using an API.

Java 8 has introduced a new Stream API that lets us process data in a declarative manner. In this quick article, we would learn how to use the Stream API to split a comma-separated String into a list of Strings and how to join a String array into a comma-separated String. We'll also look at how to convert a string array to map using Stream API. Nearly all of the time we face situations, where we need to iterate some Java Collections and filter the Collection based on some filtering logic. In a traditional approach for this type of situation, we would use lots of loops and if-else operations to get the desired result. If you want to read more about the Stream API, check Let's use the Stream API to create a function which would join a String array into a comma-separated String: public static String join(String[] arrayOfString) As we can see in the Collectors.joining() method, we are declaring our prefix as ‘[‘ and postfix as ‘]'; hence the generated String will be created with declared […..] format. 3. Splitting Strings With Stream API public static List split(String str) One interesting fact to note here is that the chars() method converts the String into a stream of Integer where each Integer value denotes the ASCII value of each and every Char sequence. That's why we need to explicitly typecast the mapper object in the mapToObj() method. 4. String Array to Map With Stream API We can also convert a String array to map using split and Collectors.toMap, provided each item in...

The Java 8 Stream API lets us process collections of data in a declarative way. The static factory methods Collectors.groupingBy() and Collectors.groupingByConcurrent() provide us with functionality similar to the ‘ GROUP BY' clause in the SQL language. We use them for grouping objects by some property and storing results in a Map instance. The overloaded methods of groupingBy are: • First, with a classification function as the method parameter: static Collector>> groupingBy(Function classifier) • Secondly, with a classification function and a second collector as method parameters: static Collector> groupingBy(Function classifier, Collector downstream) • Finally, with a classification function, a supplier method (that provides the Map implementation which contains the end result), and a second collector as method parameters: static > Collector groupingBy(Function classifier, Supplier mapFactory, Collector downstream) 2.1. Example Code Setup To demonstrate the usage of groupingBy(), let's define a BlogPost class (we will use a stream of BlogPost objects): class BlogPost 2.2. Simple Grouping by a Single Column We use the value returned by the function as a key to the map that we get from the groupingBy collector. To group the blog posts in the blog post list by their type: Map> postsPerType = posts.stream() .collect(groupingBy(BlogPost::getType)); 2.3. groupingBy with a Complex Map Key Type The classification function is not limited to returning only a scalar or String va...

Introduction A stream represents a sequence of elements and supports different kind of operations that lead to the desired result. The source of these elements is usually a Collection or an Array, from which data is provided to the stream. Streams differ from collections in several ways; most notably in that the streams are not a data structure that stores elements. They're functional in nature, and it's worth noting that operations on a stream produce a result, but do not modify its source. Sorting a List of Integers with Stream.sorted() Found within the Stream interface, the sorted() method has two overloaded variations that we'll be looking into. Both of these variations are instance methods, which require an object of its class to be created before it can be used: public final Stream sorted (){} This methods returns a stream consisting of the elements of the stream, sorted according to natural order - the ordering provided by the JVM. If the elements of the stream are not Comparable, a java.lang.ClassCastException may be thrown upon execution. Using this method is fairly simple, so let's take a look at a couple of examples: Arrays.asList( 10, 23, - 4, 0, 18).stream().sorted().forEach(System.out::println); Here, we make a List instance through the asList() method, providing a few integers and stream() them. Once streamed, we can run the sorted() method, which sorts these integers naturally. Once sorted, we've just printed them out, each in a line: - 4 0 10 18 23 If we w...

Welcome to Java 8 Stream API tutorial. In the last few java 8 posts, we looked into Java Stream. • • • • • • • • • • • • • • • • • Before we look into Java Stream API Examples, let’s see why it was required. Suppose we want to iterate over a list of integers and find out sum of all the integers greater than 10. Prior to Java 8, the approach to do it would be: private static int sumIterator(List list) If we run above program, you will get different results because it depends on the way stream is getting iterated and we don’t have any order defined for parallel processing. If we use sequential stream, then this problem will not arise. • Once a Stream is consumed, it can’t be used later on. As you can see in above examples that every time I am creating a stream. • There are a lot of methods in Stream API and the most confusing part is the overloaded methods. It makes the learning curve time taking. That’s all for Java 8 Stream example tutorial. I am looking forward to use this feature and make the code readable with better performance through parallel processing. Reference: Say I have : Assuming College2 is AlphaNum, Class90 is AlphaNum, Stud_ID10 is AlphaNum, Marks100 is number How to get the average of all student marks under University having College 1…N ? - Arnab Dutta Hello sir… am having doubt in iteration and merging. Say ,I am given with some users . And I want to iterate group to check if the user exist in any of the groups . and if the user exist in more than one ...

Introduced in Java 8, Stream API is used to process collections of objects. A stream is a sequence of objects that supports various methods which can be pipelined to produce the desired result. The features of Java stream are – • A stream is not a data structure instead it takes input from the Collections, Arrays or I/O channels. • Streams don’t change the original data structure, they only provide the result as per the pipelined methods. • Each intermediate operation is lazily executed and returns a stream as a result, hence various intermediate operations can be pipelined. Terminal operations mark the end of the stream and return the result. Different Operations On Streams Intermediate Operations 1. map: The map method is used to return a stream consisting of the results of applying the given function to the elements of this stream. List number = Arrays.asList(2,3,4,5); List square = number.stream().map(x->x*x).collect(Collectors.toList()); 2. filter: The filter method is used to select elements as per the Predicate passed as an argument. List names = Arrays.asList("Reflection","Collection","Stream"); List result = names.stream().filter(s->s.startsWith("S")).collect(Collectors.toList()); 3. sorted: The sorted method is used to sort the stream. List names = Arrays.asList("Reflection","Collection","Stream"); List result = names.stream().sorted().collect(Collectors.toList()); Terminal Operations 1. collect: The collect method is used to return the result of the intermed...

We have had a quick overview of the Java 8 Streams API in our prevous post. We looked into the power and simplicity of the Java 8 Streams API, the Intermediate and the Terminal Operations over the streams, and different ways to build streams (e.g. from collections or numerical ranges, etc.). Incontinuationof the same discussion, in this post, we will move ahead with the streams and have a look at the most important property of Java 8 Streams — laziness. If you are new to the concept of Java 8 streams, please go back and read Laziness Improves Performance? This is a really tricky question. If the laziness is utilized in the correct manner, the answer is ' yes.' Consider you are on an online shopping site and you searched for aparticulartype of a product. Usually, most of the websites will show the matching products immediately and a ' loading more'messageat the bottom. Finally, all of the search results will be loaded in parts, as described. The intent behind doing this is to keep the user interestedbyimmediatelyshowing him some of the results. While the user is browsing through the loaded products, the rest of the products are being loaded. This is because the site is delaying the complete loading of the entire product list. Consider, if the site doeseager loading or early loading of all of the products, the response time would increase and the user might get distracted to something else. While you are dealing with bigger data or infinite streams, the laziness is a real bo...