Difference Betwixt Map() In Addition To Flatmap() Inwards Coffee Eight Stream

The map() in addition to flatmap() are 2 of import operations inwards novel functional Java 8. Both represents functional performance in addition to they are also methods inwards java.util.stream.Stream class. The fundamental difference betwixt map() in addition to flatmap() function is that when yous usage map(), it applies a portion on each chemical component of current in addition to stores the value returned yesteryear the portion into a novel Stream. This way i current is transformed into to a greater extent than or less other e.g. a Stream of String is transformed into a Stream of Integer where each chemical component is length of corresponding Stream. Key affair to cry back is that the portion used for transformation inwards map() returns a unmarried value. If map() uses a function, which, instead of returning a unmarried value returns a Stream of values than yous direct maintain a Stream of Stream of values, in addition to flatmap() is used to apartment that into a Stream of values.


For example, if nosotros direct maintain a Stream of String containing {"12", "34"} in addition to a method getPermutations() which returns a listing of permuations of given String. When yous apply that portion into each String of Stream using map yous volition acquire something similar [["12","21"],["34","43"]], but if yous usage flatmap, yous acquire a Stream of Strings e.g. ["12", "21", "34", "43"]. In this aticle, we'll run across duo of working examples to empathize the divergence betwixt map() in addition to flatmap() inwards Java better.

I know it's non slow to empathize the map() in addition to flatMap() function, specially if yous direct maintain non done whatever functional programming before. I was inwards the same situation, It took me to a greater extent than or less fourth dimension to actually empathize purpose of map and flatMap in addition to cheers to Java SE 8 for Really Impatient, which helped me ot understnad these fundamental functional concepts better. The explanation given inwards this mass is actually nifty in addition to fifty-fifty if yous don't direct maintain whatever functional programming experience, yous volition understnad these novel things alongside piffling combat of effort. I highly recommend this mass to all Java developers who want to larn Java 8.

How Stream.map() industrial plant inwards Java 8

The Stream.map() portion performs map functional performance i.e. it direct maintain a Stream in addition to transform it to to a greater extent than or less other Stream. It applies a portion on each chemical component of Stream in addition to shop render value into novel Stream. This way yous tin dismiss transform a Stream of String into a Stream of Integer where Integer could survive length of String if yous render the length() function. This is a really powerful portion which is really helpful piece dealing alongside collection inwards Java.

Here is an instance of Stream.map() inwards Java 8:

List listOfIntegers = Stream.of("1", "2", "3", "4")                .map(Integer::valueOf)                .collect(Collectors.toList());

In this example, nosotros direct maintain a Stream of String values which correspond numbers, yesteryear using map() portion nosotros direct maintain converted this Stream to Stream of Integers. How? yesteryear appling Integer.valueOf() on each chemical component of Stream. That's how "1" converted to intger 1 in addition to thus on. Once transformation is done, nosotros direct maintain collected the number into a List yesteryear converting Stream to List using Collectors.

How Stream.flatMap() industrial plant inwards Java 8

The Stream.flatMap() function, every bit cite suggests, is the combination of a map in addition to a apartment operation. This way yous starting fourth dimension apply map portion in addition to than flattens the result. Key divergence is the portion used yesteryear map performance returns a Stream of values or listing of values rather than unmarried value, that's why nosotros require flattening. When yous apartment a Stream of Stream, it gets converted into Stream of values.

To empathize what flattening a current consists in, reckon a construction similar [ [1,2,3],[4,5,6],[7,8,9] ] which has "two levels". It's basicall a big List containing 3 to a greater extent than List.  Flattening this way transforming it inwards a "one level" construction e.g. [ 1,2,3,4,5,6,7,8,9 ] i.e. simply i list.

In short,
Before flattening - Stream of List of Integer
After flattening - Stream of Integer

Here is a code instance to empathize the flatMap() portion better:

List evens = Arrays.asList(2, 4, 6); List odds = Arrays.asList(3, 5, 7); List primes = Arrays.asList(2, 3, 5, 7, 11);         List numbers = Stream.of(evens, odds, primes)                .flatMap(list -> list.stream())                .collect(Collectors.toList());         System.out.println("flattend list: " + numbers);  Output: flattend list: [2, 4, 6, 3, 5, 7, 2, 3, 5, 7, 11]

You tin dismiss run across that nosotros direct maintain 3 lists which are merged into i yesteryear using flatMap() function. For mapping yous tin dismiss run across nosotros direct maintain used list.stream() portion which returns multiple values instead of unmarried value. Finally, nosotros direct maintain collected the flattend current into a list. If  you want, yous tin dismiss impress the terminal listing using forEach() method.

Stream.map() vs Stream.flatMap() inwards Java 8

In short, hither are the key difference betwixt map() vs flatMap() inwards Java 8:

• The portion yous transcend to map() performance returns a unmarried value.
• The portion yous transcend to flatMap() opeartion returns a Stream of value.
• flatMap() is combination of map in addition to apartment operation. 
• map() is used for transformation only, but flatMap() is used for both transformation in addition to flattening. 

Now let's run across a sample Java computer program to empathize the differnce betwixt flatMap() in addition to map() better.

Java Program to present divergence betwixt map vs flatMap

Here is our sample Java computer program to demonstrate the existent divergence betwixt the map() in addition to flatMap() portion of Stream cast inwards Java 8. As I told before, map() is used to transform i Stream into to a greater extent than or less other yesteryear applying a portion on each chemical component in addition to flatMap() does both transformation every bit good every bit flattening. The flatMap() portion tin dismiss direct maintain a Stream of List in addition to render Stream of values combined from all those list. In the instance below nosotros direct maintain collected the number inwards a List but yous tin dismiss also impress them using forEach() method of Java 8.

import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.stream.Collectors;  /**  * Java Program to demonstrate divergence betwixt map()  * vs flatMap() portion inwards Java 8. Both are defined  * inwards Stream class.   *  * @author WINDOWS 8  */ public class Java8Demo {      public static void main(String args[]) {          // foods which helps inwards weight loss         List<String> loseWeight = new ArrayList<>();         loseWeight.add("avocados");         loseWeight.add("beans");         loseWeight.add("salad");         loseWeight.add("oats");         loseWeight.add("broccoli");                          System.out.println("list of String : " + loseWeight);                  // let's usage map() method to convert listing of weight         // lose food, which are String to listing of ints         // which are length of each nutrient String                  List listOfInts = loseWeight.stream()                 .map(s -> s.length())                 .collect(Collectors.toList());                  System.out.println("list of ints generate yesteryear map(): " + listOfInts);                   // flatMap() example, let's starting fourth dimension creat a listing of list         List<List> listOfListOfNumber = new ArrayList<>();         listOfListOfNumber.add(Arrays.asList(2, 4));         listOfListOfNumber.add(Arrays.asList(3, 9));         listOfListOfNumber.add(Arrays.asList(4, 16));                  System.out.println("list of listing : " + listOfListOfNumber);                  // let's usage flatMap() to flatten this listing into         // listing of integers i.e. 2,4,3,9,4,16                  List listOfIntegers = listOfListOfNumber.stream()                 .flatMap( list -> list.stream())                 .collect(Collectors.toList());                  System.out.println("list of numbers generated yesteryear flatMap : " + listOfIntegers);                       }  }  Output list of String : [avocados, beans, salad, oats, broccoli] list of ints generate yesteryear map(): [8, 5, 5, 4, 8] list of list : [[2, 4], [3, 9], [4, 16]] list of numbers generated yesteryear flatMap : [2, 4, 3, 9, 4, 16]

You tin dismiss run across that inwards starting fourth dimension example, the portion used yesteryear map() method returns a unmarried value, the length of Stirng passed to it, piece inwards instance of flatMap() the method returns a stream, which is basically your multiple values.

That's all nigh difference betwixt map() in addition to flatMap() inwards Java 8. You should usage map() if yous jsut desire to transform i Stream into to a greater extent than or less other where each chemical component gets converted to i unmarried value. Use flatMap() if the portion used yesteryear map performance render multiple values in addition to yous desire simply i listing containing all values. If yous are yet confused betwixt map() vs flatMap() thus acquire read Java SE 8 for Really Impatient By Cay S. Horstmann, i of the best mass to larn nigh novel features of Java 8.

Further Learning
The Complete Java MasterClass
tutorial)

How to usage Stream cast inwards Java 8 (tutorial)

How to usage filter() method inwards Java 8 (tutorial)

How to usage forEach() method inwards Java 8 (example)

How to bring together String inwards Java 8 (example)

How to convert List to Map inwards Java 8 (solution)

How to usage peek() method inwards Java 8 (example)

5 Books to Learn Java 8 from Scratch (books)

How to convert current to array inwards Java 8 (tutorial)

Java 8 Certification FAQ (guide)

Java 8 Mock Exams in addition to Practice Test (test)

Thanks for reading this article thus far. If yous similar this article thus delight percentage alongside your friends in addition to colleagues. If yous direct maintain whatever question, doubt, or feedback thus delight drib a comment in addition to I'll seek to respond your question.

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