The presentation introduces several new features in Java 8 including lambdas, default methods, streams API, and method references. Lambdas allow for anonymous functions and simplify implementing interfaces with single methods. Default methods allow interfaces to define implementations while maintaining backwards compatibility. The streams API provides a functional-style way to process collections through filtering, mapping, matching, and reducing operations. Method references allow referring to methods without anonymous classes.

1. Java 8
Lambdas and much more
Alin Pandichi
@alinpandichi

2. About me
(Not only Java) software developer
Professional experience of 5 years
BJUG and AgileWorks community member
Twitter: @alinpandichi

3. We’ll talk about
Lambdas
Default methods
Streams
Method references

4. Java 8
Expected on 18 March 2014
Lambdas: one of the most anticipated features
Remember 'Plan B for Java 7'?

5. Play with it
https://github.com/AdoptOpenJDK/lambda-tutorial
https://jdk8.java.net/lambda/
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/

6. Lambda demo...

7. External iteration vs. Internal iteration
List<Shape> shapes = /* ... */;
for (Shape shape :shapes) {
shape.setColor(newColor);
}
shapes.forEach(shape -> shape.setColor(newColor));

8. Lambda
() -> {}

9. Lambda
() -> {}
(s) -> { System.out.println(s) }

10. Lambda
() -> {}
(s) -> { System.out.println(s) }
s -> System.out.println(s)

11. Lambda
(x, y) -> { return x + y; }

12. Lambda
(x, y) -> { return x + y; }
(x, y) -> x + y

13. Lambda
(x, y) -> { return x + y; }

14. Lambda
Adder adder = (x, y) -> { return x + y; };

15. Lambda
Adder adder = (x, y) -> { return x + y; };
public interface Adder {
public int adder(int x, int y);
}

16. Lambda
Adder adder = (x, y) -> { return x + y; };
@FunctionalInterface
public interface Adder {
public int adder(int x, int y);
}

17. Lambda
Adder adder = (x, y) -> { return x + y; };
Adder adder = new Adder() {
@Override
public int add(int x, int y) {
return x + y;
}
};

18. Iterable.forEach
public interface Iterable<T> {
Iterator<T> iterator();
}

19. Iterable.forEach
public interface Iterable<T> {
Iterator<T> iterator();
void forEach(Consumer<? super T> action);
}

20. Iterable.forEach
public interface Iterable<T> {
Iterator<T> iterator();
void forEach(Consumer<? super T> action);
}
Could break 99% of existing codebases!

21. Iterable.forEach
public interface Iterable<T> {
Iterator<T> iterator();
default void forEach(Consumer<? super T> action) {
}
}

22. Iterable.forEach
public interface Iterable<T> {
Iterator<T> iterator();
default void forEach(Consumer<? super T> action) {
Objects.requireNonNull(action);
for (T t : this) {
action.accept(t);
}
}
}

23. Before Java 8...
Interfaces contain only
method declarations and no
implementations

24. With Java 8...
Interfaces contain only
method declarations and no
implementations

25. Default methods demo...

26. Default methods
Also called:
Defender methods
Virtual extension methods

27. Default methods
Helped extending/improving the existing API
interfaces...
… without breaking the existing code...
… by providing default implementations

28. Default methods
Could be abused, for multiple inheritance!

29. Default methods
Could be abused, for multiple inheritance!
Multiple inheritance
of type - been there, done that!

30. Default methods
Could be abused, for multiple inheritance!
Multiple inheritance
of type - been there, done that!
of behaviour - you are here!

31. Default methods
Could be abused, for multiple inheritance!
Multiple inheritance
of type - been there, done that!
of behaviour - you are here!
of state - not yet, hopefully NOT EVER!

32. Default methods
interface Foo {
default void doIt() { /* foo impl */ }
}
interface Bar {
default void doIt() { /* bar impl */ }
}
class FooBar implements Foo, Bar {}
Will not compile

33. Default methods
interface Foo {
default void doIt() { /* foo impl */ }
}
interface Bar {
default void doIt() { /* bar impl */ }
}
class FooBar implements Foo, Bar {
@Override
public void doIt() { Foo.super.doIt(); }
}

34. Streams API demo...

35. Streams API
Nothing to do with I/O Streams

36. Streams API
Nothing to do with I/O Streams
A pipes-and-filters based API for collections

37. Streams API
Nothing to do with I/O Streams
A pipes-and-filters based API for collections
This may be familiar...
ps -ef | grep java | cut -c 1-9 | sort -n | uniq

38. Streams API
Nothing to do with I/O Streams
A 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();

39. Method references
documents
.map(d -> d.getTitle())
.collect(toList());

40. Method references
documents
.map(d -> d.getTitle())
.collect(toList());
Does nothing but call an existing method...

41. Method references
documents
.map(d -> d.getTitle())
.collect(toList());
documents
.map(Document::getTitle)
.collect(toList());

42. Method references
to a static method
ContainingClass::staticMethodName

43. Method references
to a static method
ContainingClass::staticMethodName
to an instance method of a particular object
containingObject::instanceMethodName

44. Method references
to a static method
ContainingClass::staticMethodName
to an instance method of a particular object
containingObject::instanceMethodName
to a constructor
ClassName::new

45. See also...
● JSR 310: Date and Time API
No more java.util.Calendar!!!
● Nashorn, the new Javascript engine
var HelloUser = Java.type("com.credera.example.HelloUser");
var helloUser = new HelloUser("John");
print(helloUser.getMessage())
$ jjs -cp /com/credera/example/HelloUser TestNashorn.js

46. Recap
Lambdas
Default methods
Streams
Method references

47. Play with it
https://github.com/AdoptOpenJDK/lambda-tutorial
https://jdk8.java.net/lambda/
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/