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 back at the journeying of for loop inwards dissimilar versions of Java programming language. for loop is in that place from the really outset of Java i.e. JDK 1.0. Almost all Java programmers stimulate got used the classical for() loop, every bit it is also an essential programming construct, I justice simply adjacent to if-else, but when the foreach loop or every bit some people telephone telephone it enhanced for loop was introduced inwards JDK 1.5, everything changed from looping over Collection together with array perspective. Yesterday's pop looping fix leave of absence quondam together with ugly together with to a greater extent than elegant solution took over. It was shorter, cleaner together with less mistake prone, what else y'all demand at that time.

Things were quite inwards damage of for loop from final 10 years, but  In Java 8, looping has taken some other big measuring inwards its novel avatar, forEach() method. Its non alone short, fix clean but also accept wages of lazy evaluation together with 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 together with less mistake prone than previous 1 together with everybody loved it. You don't demand to continue rails of index, y'all don't demand to telephone telephone size() method inwards every measuring together with it was less mistake prone than previous one, but it was nevertheless imperative. You are telling compiler what to practice together with how to practice similar traditional for loop.

Things modify drastically when the functional trend of programming was introduced inwards Java 8 via lambda expression together with novel Stream API. Now y'all tin loop over your collection without whatever loop inwards Java, y'all simply demand to exercise forEach() method of java.util.Stream class, every bit shown below :

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

This code has reduced looping over collection or listing into simply 1 line. To add together into, If y'all desire to perform some pre processing work e.g. filtering, conversion or mapping, y'all tin also practice this inwards the same describe every bit shown below :

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

This code volition instantly alone impress "India" together with "England" every bit it contains the alphabetic quality "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 wages over previous ii imperative approaches, initiatory of all it segregate what to practice from how to do. You are simply telling API to filter listing based upon status y'all stimulate got given together with therefore impress those element. Now API tin impress it past times the way it wants, y'all don't demand to worry about. Benefit is, y'all don't demand to write imperative code, y'all volition also practice goodness from lazy evaluation together with whatever functioning 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, every bit shown below :

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

That "::" or range resolution operator of C++ is used for method reference, since y'all are non doing anything amongst String declaration of println() therefore simply passing it, y'all tin exercise method reference in that place to brand your code to a greater extent than fix clean together with concise.

Here is the consummate code event of using dissimilar for loops inwards Java world, including Java 8 forEach() method. This event demonstrate gradual changes made inwards for loop from Java 1.4, five together with 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 together with Java 8 earth 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 tardily to loop over         // List or Collection                 for(String province : countries){             System.out.println(country);         }                  // In Java 8, y'all tin exercise 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 every bit 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 y'all stimulate got seen, for loop has come upward a long way from JDK 1 to JDK 8, peculiarly when y'all exercise amongst Collection. Gone are the days, when y'all demand to worry virtually looping index, initializing it properly, making certain it ends properly to avoid IndexOutOfBoundsException together with calling corresponding get() method on List. Java five was initiatory of all measuring inwards making looping over Collection tardily but Java 8 has provided a much powerful of functional trend looping inwards Java. In fact, it's non fifty-fifty a loop its simply a method call, which agency y'all tin write high-performance Java Collection code without using a loop.

So adjacent time, y'all demand to loop over collection, simply don't exercise a unproblematic or advanced for loop, considering using forEach() method of Stream. You volition non alone practice goodness from modern way of filtering together with mapping but also from lazy evaluation together with functioning improvement past times smart looping implementation of API itself.

Further Learning
The Complete Java MasterClass
tutorial)

How to exercise Stream shape inwards Java 8 (tutorial)

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

How to exercise 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 exercise 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 together with Practice Test (test)

Thanks for reading this article therefore far. If y'all similar this article therefore delight portion amongst your friends together with colleagues. If y'all stimulate got whatever question, doubt, or feedback therefore delight drib a comment together with I'll endeavor to response your question.

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

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

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