Java Viii - Journeying Of For Loop Inwards Java, For(Index) To Foreach()

for loop has come upwards a long way inward Java 8 amongst novel forEach() method in java.util.stream.Stream class. In this article, nosotros volition accept a hold off at the journeying of for loop inward unlike versions of Java programming language. for loop is in that place from the real kickoff of Java i.e. JDK 1.0. Almost all Java programmers cause got used the classical for() loop, equally it is also an essential programming construct, I approximate merely adjacent to if-else, but when the foreach loop or equally some people telephone telephone it enhanced for loop was introduced inward JDK 1.5, everything changed from looping over Collection together with array perspective. Yesterday's pop looping build acquire quondam together with ugly together with to a greater extent than elegant solution took over. It was shorter, cleaner together with less fault prone, what else you lot demand at that time.

Things were quite inward price of for loop from concluding 10 years, but  In Java 8, looping has taken some other big measuring inward its novel avatar, forEach() method. Its non alone short, gear upwards clean but also accept wages of lazy evaluation together with inward built parallelism of Java 8 Stream. let's revisit this journeying of for loop inward Java inward this post service of .


Pre-JDK 1.5, this was my favorite way of iterating over an ArrayList or HashSet :

// pre JDK 1.5, printing each chemical cistron of List using for loop List<String> countries = Arrays.asList("India", "Australia", "England", "South Africa");          for(int i=0; i < countries.size(); i++){    System.out.println(countries.get(i)); }

So when foreach loop or advanced for loop was added on Java 5, I chop-chop adopted to next trend of looping over Collection or List :

for(String terra firma : countries){      System.out.println(country); }

This was much shorter, cleaner together with less fault prone than previous i together with everybody loved it. You don't demand to buy the farm on rail of index, you lot don't demand to telephone telephone size() method inward every measuring together with it was less fault prone than previous one, but it was all the same imperative. You are telling compiler what to exercise together with how to exercise similar traditional for loop.

Things modify drastically when the functional trend of programming was introduced inward Java 8 via lambda expression together with novel Stream API. Now you lot tin loop over your collection without whatever loop inward Java, you lot merely demand to utilization forEach() method of java.util.Stream class, equally shown below :

countries.stream().forEach(str -> System.out.println(str));

This code has reduced looping over collection or listing into merely i line. To add together into, If you lot desire to perform some pre processing describe e.g. filtering, conversion or mapping, you lot tin also exercise this inward the same describe equally shown below :

countries.stream()          .filter(country -> country.contains("n"))          .forEach(str -> System.out.println(str));

This code volition forthwith alone impress "India" together with "England" equally it contains the missive of the alphabet "n". Java SE 8 for Really Impatient By Cay S. Horstmann  to larn to a greater extent than nearly filtering inward Java 8.

This approach has several wages over previous 2 imperative approaches, initiative off it segregate what to exercise from how to do. You are merely telling API to filter listing based upon status you lot cause got given together with and thus impress those element. Now API tin impress it past times the way it wants, you lot don't demand to worry about. Benefit is, you lot don't demand to write imperative code, you lot volition also exercise goodness from lazy evaluation together with whatever surgical physical care for improvement done past times API to achieve your task. You tin fifty-fifty brand your code to a greater extent than concise using method reference characteristic of Java 8, equally shown below :

countries.stream()          .filter(country -> country.contains("n"))          .forEach(System.out::println);

That "::" or orbit resolution operator of C++ is used for method reference, since you lot are non doing anything amongst String declaration of println() together with thus merely passing it, you lot tin utilization method reference in that place to brand your code to a greater extent than gear upwards clean together with concise.

Here is the consummate code instance of using unlike for loops inward Java world, including Java 8 forEach() method. This instance demonstrate gradual changes made inward for loop from Java 1.4, v together with Java 8 versions.

package test;  import java.io.IOException; import java.util.Arrays; import java.util.List;   /**  * Java Program to demonstrate unlike ways to loop over collection inward   * pre Java 8 together with Java 8 the world using Stream's forEach method.  * @author Javin Paul  */ public class JourneyOfForLoopInJava {      public static void main(String args[]) throws IOException {          // pre JDK 1.5, printing each chemical cistron of List using for loop         List<String> countries = Arrays.asList("India", "Australia", "England", "South Africa");                  for(int i=0; i<countries.size(); i++){             System.out.println(countries.get(i));         }                           // In Java 5, nosotros god advanced for loop, which makes it slowly to loop over         // List or Collection                 for(String terra firma : countries){             System.out.println(country);         }                  // In Java 8, you lot tin utilization forEach method of Stream shape to loop over         // whatever List or Collection         countries.stream().forEach(str -> System.out.println(str));                  // doing some pre-processing filtering on our list     // volition impress India, England equally alone they comprise "n"         countries.stream()                 .filter(country -> country.contains("n"))                 .forEach(str -> System.out.println(str));                  // making the code to a greater extent than concise using method reference          countries.stream()                 .filter(country -> country.contains("n"))                 .forEach(System.out::println);     }   }

So you lot cause got seen, for loop has come upwards a long way from JDK 1 to JDK 8, peculiarly when you lot utilization amongst Collection. Gone are the days, when you lot demand to worry nearly looping index, initializing it properly, making certain it ends properly to avoid IndexOutOfBoundsException together with calling corresponding get() method on List. Java v was initiative off measuring inward making looping over Collection slowly but Java 8 has provided a much powerful of functional trend looping inward Java. In fact, it's non fifty-fifty a loop its merely a method call, which agency you lot tin write high-performance Java Collection code without using a loop.

So adjacent time, you lot demand to loop over collection, merely don't utilization a uncomplicated or advanced for loop, considering using forEach() method of Stream. You volition non alone exercise goodness from modern way of filtering together with mapping but also from lazy evaluation together with surgical physical care for improvement past times smart looping implementation of API itself.

Further Learning
The Complete Java MasterClass
tutorial)

How to utilization Stream shape inward Java 8 (tutorial)

How to utilization filter() method inward Java 8 (tutorial)

How to utilization forEach() method inward Java 8 (example)

How to bring together String inward Java 8 (example)

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

How to utilization peek() method inward Java 8 (example)

5 Books to Learn Java 8 from Scratch (books)

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

Java 8 Certification FAQ (guide)

Java 8 Mock Exams together with Practice Test (test)

Thanks for reading this article thus far. If you lot similar this article together with thus delight portion amongst your friends together with colleagues. If you lot cause got whatever question, doubt, or feedback together with thus delight drib a comment together with I'll attempt to response your question.

P.S. : Java 8 is bundle of many exciting features similar this, if you lot are interested to larn to a greater extent than nearly them, you lot tin alternative whatever of the next books :

• Java 8 inward Action: Lambdas, Streams, together with functional-style programming (see here)
• Mastering Lambdas: Java Programming inward a Multicore World (see here)