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

for loop has come upward a long way inwards 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 inwards dissimilar 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 estimate only adjacent to if-else, but when the foreach loop or equally some people telephone phone it enhanced for loop was introduced inwards JDK 1.5, everything changed from looping over Collection in addition to array perspective. Yesterday's pop looping build acquire one-time in addition to ugly in addition to to a greater extent than elegant solution took over. It was shorter, cleaner in addition to less mistake prone, what else you lot demand at that time.

Things were quite inwards price of for loop from final 10 years, but  In Java 8, looping has taken some other big measurement inwards its novel avatar, forEach() method. Its non alone short, gear upward clean but also accept payoff of lazy evaluation in addition to inwards built parallelism of Java 8 Stream. let's revisit this journeying of for loop inwards Java inwards 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 speedily adopted to next trend of looping over Collection or List :

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

This was much shorter, cleaner in addition to less mistake prone than previous ane in addition to everybody loved it. You don't demand to continue rail of index, you lot don't demand to telephone phone size() method inwards every measurement in addition to it was less mistake prone than previous one, but it was however imperative. You are telling compiler what to practice in addition to how to practice similar traditional for loop.

Things alter drastically when the functional trend of programming was introduced inwards Java 8 via lambda expression in addition to novel Stream API. Now you lot tin terminate loop over your collection without whatever loop inwards Java, you lot only demand to utilisation 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 only ane line. To add together into, If you lot desire to perform some pre processing chore e.g. filtering, conversion or mapping, you lot tin terminate also practice this inwards the same draw of piece of job equally shown below :

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

This code volition instantly alone impress "India" in addition to "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 virtually filtering inwards Java 8.

This approach has several payoff over previous 2 imperative approaches, initiative off it segregate what to practice from how to do. You are only telling API to filter listing based upon status you lot cause got given in addition to thence impress those element. Now API tin terminate 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 practice goodness from lazy evaluation in addition to whatever functioning improvement done past times API to range your task. You tin terminate 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() thence only passing it, you lot tin terminate utilisation method reference in that place to brand your code to a greater extent than gear upward clean in addition to concise.

Here is the consummate code instance of using dissimilar for loops inwards Java world, including Java 8 forEach() method. This instance demonstrate gradual changes made inwards for loop from Java 1.4, five in addition to Java 8 versions.

package test;  import java.io.IOException; import java.util.Arrays; import java.util.List;   /**  * Java Program to demonstrate dissimilar ways to loop over collection inwards   * pre Java 8 in addition to Java 8 globe 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 slow to loop over         // List or Collection                 for(String province : countries){             System.out.println(country);         }                  // In Java 8, you lot tin terminate utilisation 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 incorporate "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 upward a long way from JDK 1 to JDK 8, specially when you lot utilisation amongst Collection. Gone are the days, when you lot demand to worry virtually looping index, initializing it properly, making certain it ends properly to avoid IndexOutOfBoundsException in addition to calling corresponding get() method on List. Java five was initiative off measurement inwards making looping over Collection slow but Java 8 has provided a much powerful of functional trend looping inwards Java. In fact, it's non fifty-fifty a loop its only a method call, which way you lot tin terminate write high-performance Java Collection code without using a loop.

So adjacent time, you lot demand to loop over collection, only don't utilisation a uncomplicated or advanced for loop, considering using forEach() method of Stream. You volition non alone practice goodness from modern way of filtering in addition to mapping but also from lazy evaluation in addition to functioning improvement past times smart looping implementation of API itself.

Further Learning
The Complete Java MasterClass
tutorial)

How to utilisation Stream shape inwards Java 8 (tutorial)

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

How to utilisation 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 utilisation 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 thence far. If you lot similar this article thence delight percentage amongst your friends in addition to colleagues. If you lot cause got whatever question, doubt, or feedback thence delight drib a comment in addition to I'll crusade to respond 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 virtually them, you lot tin terminate selection whatever of the next books :

• Java 8 inwards Action: Lambdas, Streams, in addition to functional-style programming (see here)
• Mastering Lambdas: Java Programming inwards a Multicore World (see here)

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