Java 8 Features Tutorial - The ULTIMATE Guide (PDF Download)EDITORIAL NOTE: It’s been a while since Java 8 is out in the public and everything points to the fact that this is a really major release. We have provided an abundance of tutorials here at Java Code Geeks, like Playing with Java 8 – Lambdas and Concurrency, Java 8 Date Time API Tutorial : Local. Date. Time and Abstract Class Versus Interface in the JDK 8 Era. We also referenced 1.
Must Read Java 8 Tutorials from other sources. Of course, we examined some of the shortfalls also, like The Dark Side of Java 8. Now, it is time to gather all the major Java 8 features under one reference post for your reading pleasure.
Enjoy! 1. Introduction. With no doubts, Java 8 release is the greatest thing in the Java world since Java 5 (released quite a while ago, back in 2. It brings tons of new features to the Java as a language, its compiler, libraries, tools and the JVM (Java virtual machine) itself.
Additionally, to verify the availability of parameter names, there is a handy method isNamePresent() provided by Parameter class. 4. New Features in Java libraries. JCGs (Java Code Geeks) is an independent online community focused on creating the ultimate Java to Java developers resource center; targeted at the technical. We have already learned about reading and writing excel files in java using apache POI library. In this tutorial, I am writing various code examples to create PDF. An annotation, in the Java computer programming language, is a form of syntactic metadata that can be added to Java source code. [1] Classes, methods, variables. Java2s.com | Email:info at java2s.com | © Demo Source and Support. All rights reserved. This tutorial uses the latest version of Java (Java 8) throughout, covers modern syntax and approaches, and focuses primarily on those parts of Java that apply to all.
In this tutorial we are going to take a look on all these changes and demonstrate the different usage scenarios on real examples. The tutorial consists of several parts where each one touches the specific side of the platform: languagecompilerlibrariestoolsruntime (JVM)2. New Features in Java language. Java 8 is by any means a major release. One might say it took so long to finalize in order to implement the features every Java developer was looking for.
In this section we are going to cover most of them. Lambdas and Functional Interfaces. Lambdas (also known as closures) are the biggest and most awaited language change in the whole Java 8 release. They allow us to treat functionality as a method argument (passing functions around), or treat a code as data: the concepts every functional developer is very familiar with. Many languages on JVM platform (Groovy, Scala, …) have had lambdas since day one, but Java developers had no choice but hammer the lambdas with boilerplate anonymous classes.
Using Bean Validation. Validating input received from the user to maintain data integrity is an important part of application logic. Validation of data can take place. Java 8 Tutorial: Lambda Expressions, Streams, and More Interested in live training from the author of these tutorials? See the upcoming Java 8 and general Java.
Lambdas design discussions have taken a lot of time and community efforts. But finally, the trade- offs have been found, leading to new concise and compact language constructs. In its simplest form, a lambda could be represented as a comma- separated list of parameters, the –> symbol and the body. For example: Arrays. List( "a", "b", "d" ). Each( e - > System.
Jersey is the reference implementation for the JSR 311 specification. The Jersey implementation. The Java EE 6 Tutorial Eric Jendrock Ricardo Cervera-Navarro Ian Evans Devika Gollapudi Kim Haase William Markito Chinmayee Srivathsa January 2013.
Please notice the type of argument e is being inferred by the compiler. Alternatively, you may explicitly provide the type of the parameter, wrapping the definition in brackets. For example: Arrays. List( "a", "b", "d" ).
Each( ( String e ) - > System. In case lambda’s body is more complex, it may be wrapped into square brackets, as the usual function definition in Java.
For example: Arrays. List( "a", "b", "d" ). Each( e - > {. System. out. print( e ). System. out. print( e ). Lambdas may reference the class members and local variables (implicitly making them effectively final if they are not).
For example, those two snippets are equivalent: String separator = ",". Arrays. as. List( "a", "b", "d" ). Each(. ( String e ) - > System. And: final String separator = ",". Arrays. as. List( "a", "b", "d" ). Each(. ( String e ) - > System. Lambdas may return a value.
The type of the return value will be inferred by compiler. The return statement is not required if the lambda body is just a one- liner. The two code snippets below are equivalent: Arrays. List( "a", "b", "d" ). To( e. 2 ) ); And: Arrays. List( "a", "b", "d" ). To( e. 2 ). return result.
Language designers put a lot of thought on how to make already existing functionality lambda- friendly. As a result, the concept of functional interfaces has emerged. The function interface is an interface with just one single method. As such, it may be implicitly converted to a lambda expression. The java. lang. Runnable and java.
Callable are two great examples of functional interfaces. In practice, the functional interfaces are fragile: if someone adds just one another method to the interface definition, it will not be functional anymore and compilation process will fail. To overcome this fragility and explicitly declare the intent of the interface as being functional, Java 8 adds special annotation @Functional. Interface (all existing interfaces in Java library have been annotated with @Functional. Interface as well). Let us take a look on this simple functional interface definition: @Functional.
Interface. public interface Functional {. One thing to keep in mind: default and static methods do not break the functional interface contract and may be declared: @Functional. Interface. public interface Functional. Default. Methods {. Method() {. }Lambdas are the largest selling point of Java 8.
It has all the potential to attract more and more developers to this great platform and provide state of the art support for functional programming concepts in pure Java. For more details please refer to official documentation. Interface’s Default and Static Methods. Java 8 extends interface declarations with two new concepts: default and static methods. Default methods make interfaces somewhat similar to traits but serve a bit different goal. They allow adding new methods to existing interfaces without breaking the binary compatibility with the code written for older versions of those interfaces.
The difference between default methods and abstract methods is that abstract methods are required to be implemented. But default methods are not. Instead, each interface must provide so called default implementation and all the implementers will inherit it by default (with a possibility to override this default implementation if needed). Let us take a look on example below. Defaulable {. // Interfaces now allow default methods, the implementer may or.
String not. Required() {. Default implementation".
Defaultable. Impl implements Defaulable {. Overridable. Impl implements Defaulable {. String not. Required() {. Overridden implementation". The interface Defaulable declares a default method not. Required() using keyword default as part of the method definition. One of the classes, Defaultable.
Impl, implements this interface leaving the default method implementation as- is. Another one, Overridable. Impl , overrides the default implementation and provides its own. Another interesting feature delivered by Java 8 is that interfaces can declare (and provide implementation) of static methods. Here is an example.
Defaulable. Factory {. Interfaces now allow static methods. Defaulable create( Supplier< Defaulable > supplier ) {. The small code snippet below glues together the default methods and static methods from the examples above. String[] args ) {. Defaulable defaulable = Defaulable. Factory. create( Defaultable.
Impl: :new ). System. Required() ). defaulable = Defaulable. Factory. create( Overridable. Impl: :new ). System.
Required() ). }The console output of this program looks like that: Default implementation. Overridden implementation. Default methods implementation on JVM is very efficient and is supported by the byte code instructions for method invocation. Default methods allowed existing Java interfaces to evolve without breaking the compilation process. The good examples are the plethora of methods added to java. Collection interface: stream(), parallel. Stream(), for. Each(), remove.
If(), …Though being powerful, default methods should be used with a caution: before declaring method as default it is better to think twice if it is really needed as it may cause ambiguity and compilation errors in complex hierarchies. For more details please refer to official documentation. Method References. Method references provide the useful syntax to refer directly to exiting methods or constructors of Java classes or objects (instances). With conjunction of Lambdas expressions, method references make the language constructs look compact and concise, leaving off boilerplate. Below, considering the class Car as an example of different method definitions, let us distinguish four supported types of method references.
Car {. public static Car create( final Supplier< Car > supplier ) {. Car car ) {. System. Collided " + car. String() ). public void follow( final Car another ) {. System. out. println( "Following the " + another. String() ). public void repair() {.
System. out. println( "Repaired " + this. String() ). }The first type of method references is constructor reference with the syntax Class: :new or alternatively, for generics, Class< T > :: new. Please notice that the constructor has no arguments. Car car = Car. create( Car: :new ). List< Car > cars = Arrays.
List( car ); The second type is reference to static method with the syntax Class: :static_method. Please notice that the method accepts exactly one parameter of type Car. Each( Car: :collide ); The third type is reference to instance method of arbitrary object of specific type with the syntax Class: :method. Please notice, no arguments are accepted by the method. Each( Car: :repair ); And the last, fourth type is reference to instance method of particular class instance the syntax instance: :method.
Please notice that method accepts exactly one parameter of type Car. Car police = Car.
Car: :new ). cars. Each( police: :follow ); Running all those examples as a Java program produces following output on a console (the actual Car instances might be different): Collided [email protected]8. Repaired [email protected]8. Following the [email protected]8. For more examples and details on method references, please refer to official documentation.
Repeating annotations. Since Java 5 introduced the annotations support, this feature became very popular and is very widely used. However, one of the limitations of annotation usage was the fact that the same annotation cannot be declared more than once at the same location. Java 8 breaks this rule and introduced the repeating annotations. It allows the same annotation to be repeated several times in place it is declared. The repeating annotations should be themselves annotated with @Repeatable annotation.