1. Java 8 Features
Lenin Kumar Koppoju

2. Agenda
• Default Methods
• Static Methods
• Method Reference Operator
• Lambda Expressions (Streams API)

3. Default Method
• This is a new feature, which allows developer to add new methods to the
interface using default keyword without breaking existing implementation.
• Object class methods are not allowed as default methods.

4. Extending Interfaces that contain default
methods
• Not mention the default method at all, which lets your extended interface
inherit the default method.
• Re-declare the default method, which makes it abstract.
• Re-define the default method, which overrides it.

5. Scenario 1: Implementing multiple Interfaces
those contain same name default method
• Use the super keyword to invoke a default method in both classes and
interfaces.

6. Scenario 2: Implementing Interfaces and
class, those contain same method
• Instance methods are preferred over interface default methods.

7. Static Method
• This is an extension, which allows developer to add new methods to the
interface using static keyword without breaking existing implementation.
• Object class methods are not allowed as static methods.

8. Static Method
• Static Methods are belongs to class.
• These methods never override.
• Default or general methods never override with Static Methods in sub
classes.

9. Method Reference Operator
• A new powerful operator, added with Java 8.
• This operator calls in following ways
• Class :: Static_Method
• Class :: Method
• Instance :: Method

10. Method Reference Operator
• Keywords super and this can be used with method references.

11. Lambda Expressions
• A new feature, which allows to write functional programming.

12. Lambda Expressions
• Functional Interface
• This is an Interface with a single abstract method, called the functional method for that
functional interface, to which the lambda expression's parameter and return types are
matched or adapted.
• It provides target types for lambda expressions and method references.
• Use @FunctionalInterface annotation to identify/confirm functional interface.

13. Lambda Expressions
• Functional Interface
• These interfaces can provide a target type in multiple contexts, such as assignment
context, method invocation, or cast context.

14. Lambda Expressions
• Base functional interfaces, which are used frequently in lambda’s.
• Consumer – consumes one argument, returns nothing
• Function – takes one argument, returns one value.
• Predicate – checks one argument, returns Boolean (true or false).
• Supplier – accepts no argument, returns one value.

15. Lambda Expressions
• Base functional interfaces, for our notes.
• Consumer – process and returns nothing.
• Function – used for mapping, process and returns something.
• Predicate – used for condition, process and returns true or false.
• Supplier – used as a factory, process and returns instance.

16. Lambda Expressions
• Stream API
• This is newly added API in java.util.stream.
• This introduces real world functional-style programming into java.
• ThisAPI has simplified the collections processing.
• You can create streams from collections, arrays, generators, or iterators.

17. Lambda Expressions
• Stream API
• Stream class will create Streams with the help of static methods : contact, empty,
generate, iterate, of.

18. Lambda Expressions
• Streams in parallel
• Parallel Stream can be created using Stream.parallel or Collection.parallerStream
methods.
• This will partition the stream into multiple substreams.
• Aggregate operations iterate over and process these substreams in parallel and then
combine the results.

19. Lambda Expressions
• Optional
• This a new class added in java.util package to avoid NullPointerException.
• A container object which may or may not contain a non-null value. If a value is present,
isPresent() will return true and get() will return the value.
• Frequently,This class used to be created to return value on safe operations and we can
create using static methods : empty, ofNullable, of.

20. Lambda Expressions
• Comparator
• This Provides comparison functionality,Which imposes ordering on collection of
objects.
• This is a functional interface with compare abstract method.
• New static methods are added for convenience to create comparators, multiple value
comparing, null values ordering and reverse order.

21. Lambda Expressions
• Optional
• Getting Optional as return on Stream operations : max, min, reduce, findAny,
findFirst.

22. Lambda Expressions
• We can convert the streams to other type using map, mapToXXX (Double,
Int, Long) methods.
• These conversion streams will be used get statistics like sum, average, max,
min, count.

23. Lambda Expressions
• Stream’s Review

24. Lambda Expressions
• Optional’s Review

25. Lambda Expressions
• Collectors – to create collects like list, set and map.

26. Lambda Expressions
• Partitioning

27. Lambda Expressions
• Grouping

28. Lambda Expressions
• Statistics

29. Thank you…
Lenin Kumar Koppoju