java 8 - lambdas and much more
DESCRIPTION
Java 8 - Lambdas, default methods, streams API, method referencesTRANSCRIPT
Lambdas and much more
Java 8
Alin Pandichi@alinpandichi
(Not only Java) software developer
Professional experience of 5 years
BJUG and AgileWorks community member
Twitter: @alinpandichi
About me
Lambdas
Default methods
Streams
Method references
We’ll talk about
Expected on 18 March 2014
Lambdas: one of the most anticipated features
Remember 'Plan B for Java 7'?
Java 8
https://github.com/AdoptOpenJDK/lambda-tutorial
https://jdk8.java.net/lambda/
Play with it
IDE support:http://www.jetbrains.com/idea/download/http://wiki.eclipse.org/JDT/Eclipse_Java_8_Support_(BETA)http://bits.netbeans.org/dev/nightly/latest/
Lambda demo...
External iteration vs. Internal iteration
List<Shape> shapes = /* ... */;
for (Shape shape :shapes) {shape.setColor(newColor);
}
shapes.forEach(shape -> shape.setColor(newColor));
() -> {}
Lambda
() -> {}
(s) -> { System.out.println(s) }
Lambda
() -> {}
(s) -> { System.out.println(s) }
s -> System.out.println(s)
Lambda
(x, y) -> { return x + y; }
Lambda
(x, y) -> { return x + y; }
(x, y) -> x + y
Lambda
(x, y) -> { return x + y; }
Lambda
Adder adder = (x, y) -> { return x + y; };
Lambda
Adder adder = (x, y) -> { return x + y; };
Lambda
public interface Adder {public int adder(int x, int y);
}
Adder adder = (x, y) -> { return x + y; };
Lambda
public interface Adder {public int adder(int x, int y);
}
@FunctionalInterface
Adder adder = (x, y) -> { return x + y; };
Lambda
Adder adder = new Adder() {@Overridepublic int add(int x, int y) {
return x + y;}
};
Iterable.forEachpublic interface Iterable<T> {
Iterator<T> iterator();
}
Iterable.forEachpublic interface Iterable<T> {
Iterator<T> iterator();void forEach(Consumer<? super T> action);
}
Iterable.forEachpublic interface Iterable<T> {
Iterator<T> iterator();void forEach(Consumer<? super T> action);
}
Could break 99% of existing codebases!
Iterable.forEachpublic interface Iterable<T> {
Iterator<T> iterator();default void forEach(Consumer<? super T> action) {}
}
Iterable.forEachpublic interface Iterable<T> {
Iterator<T> iterator();default void forEach(Consumer<? super T> action) {
Objects.requireNonNull(action); for (T t : this) { action.accept(t); }}
}
Interfaces contain only method declarations and no implementations
Before Java 8...
Interfaces contain only method declarations and no implementations
With Java 8...
Default methods demo...
Also called:Defender methodsVirtual extension methods
Default methods
Helped extending/improving the existing API interfaces...
… without breaking the existing code...
… by providing default implementations
Default methods
Could be abused, for multiple inheritance!
Default methods
Could be abused, for multiple inheritance!
Multiple inheritanceof type - been there, done that!
Default methods
Could be abused, for multiple inheritance!
Multiple inheritanceof type - been there, done that!of behaviour - you are here!
Default methods
Could be abused, for multiple inheritance!
Multiple inheritanceof type - been there, done that!of behaviour - you are here!of state - not yet, hopefully NOT EVER!
Default methods
interface Foo {default void doIt() { /* foo impl */ }
}interface Bar {
default void doIt() { /* bar impl */ }}class FooBar implements Foo, Bar {}
Will not compile
Default methods
interface Foo {default void doIt() { /* foo impl */ }
}interface Bar {
default void doIt() { /* bar impl */ }}class FooBar implements Foo, Bar {
@Overridepublic void doIt() { Foo.super.doIt(); }
}
Default methods
Streams API demo...
Nothing to do with I/O Streams
Streams API
Nothing to do with I/O StreamsA pipes-and-filters based API for collections
Streams API
Nothing to do with I/O StreamsA pipes-and-filters based API for collections
This may be familiar...ps -ef | grep java | cut -c 1-9 | sort -n | uniq
Streams API
Nothing to do with I/O StreamsA pipes-and-filters based API for collections
This may be familiar...ps -ef | grep java | cut -c 1-9 | sort -n | uniq
In a similar manner...blocks.stream()
.filter(b -> b.getColor() == Color.RED)
.mapToInt(b -> b.getWeight()).sum();
Streams API
documents.map(d -> d.getTitle()).collect(toList());
Method references
documents.map(d -> d.getTitle()).collect(toList());
Does nothing but call an existing method...
Method references
documents.map(d -> d.getTitle()).collect(toList());
documents.map(Document::getTitle).collect(toList());
Method references
to a static method ContainingClass::staticMethodName
Method references
to a static method ContainingClass::staticMethodName
to an instance method of a particular objectcontainingObject::instanceMethodName
Method references
to a static method ContainingClass::staticMethodName
to an instance method of a particular objectcontainingObject::instanceMethodName
to a constructorClassName::new
Method references
● JSR 310: Date and Time APINo more java.util.Calendar!!!
● Nashorn, the new Javascript enginevar HelloUser = Java.type("com.credera.example.HelloUser");
var helloUser = new HelloUser("John");print(helloUser.getMessage())
$ jjs -cp /com/credera/example/HelloUser TestNashorn.js
See also...
Lambdas
Default methods
Streams
Method references
Recap
https://github.com/AdoptOpenJDK/lambda-tutorial
https://jdk8.java.net/lambda/
Play with it
IDE support:http://www.jetbrains.com/idea/download/http://wiki.eclipse.org/JDT/Eclipse_Java_8_Support_(BETA)http://bits.netbeans.org/dev/nightly/latest/