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Java 8 Functional Programming - I
- 1. Functional Programming in Java 8 - I
- 2. Context ✓ Lambda Expressions ✓ Built-in Functional Interfaces ✓ Optionals
- 3. Writing Simple Lambdas —> A lambda expression is a block of code that gets passed around. A lambda expression can be thought as a continued anonymous method. A lambda expression has parameters and a body just like regular methods do, but it doesn’t have a name like a real method.
- 4. Lambda Syntax • The concise way The verbose way They are all valid
- 5. Which Variables Can My Lambda Access? • Lambdas are allowed to access instance and static variables. • Method parameters and local variables could be used if they are not assigned new values. Finals and effectively final variables.
- 6. Functional Interface • A Functional Interface has exactly one abstract method. • It could have any numbers of default methods.
- 7. Built-In Functional Interfaces • Java 8 provides built-in functional interfaces in java.util.function package. Interface Parameters Return Type Method Supplier<T> 0 T get Consumer<T> 1(T) void accept BiConsumer<T,U> 2(T,U) void accept Predicate<T> 1(T) boolean test BiPredicate<T> 2(T,U) boolean test UnaryOperator<T> 1(T) T apply BinaryOperator<T,T> 2(T,T) T apply Function<T,R> 1(T) R apply BiFunction<T,U,R> 2(T,U) R apply
- 8. Implementing Supplier • Supplier interfaced is used when you want to generate or supply values without taking parameters. • Related method name is get().
- 9. Implementing Consumers • Consumer interfaces used when you want to do something with parameter but not return anything. • Related method name is accept().
- 10. Implementing Predicates • Predicates are often used for distinguishing elements. • Related method name is test(). And() and Negate() are useful default methods.
- 11. Implementing Functions • Functions take parameters and return values possibly in different type. • Related method name is apply().
- 12. Implementing Operators • UnaryOperator and BinaryOperator are types of specialised functions. • Related method name is apply().
- 13. Implementing Custom Functional Interface • Creating our own custom interface is an option.
- 14. Optionals • An optional could have a value inside or not. • Optional.empty() Optional.of() 100.0
- 15. Optional Methods Method Optional Empty Optional with Value get() Throws an Exception Returns value ifPresent() Returns false Returns true ifPresent(Consumer cons) Does nothing Calls consumer orElse(T other) Returns other parameter Returns value orElseThrow(Supplier s) Throws supplied exception Returns value orElseGet(Supplier s) Returns supplied value Returns value
- 16. Optional Methods • Returning an optional instead of null is more clear statement that tells there might be no value. • Usage of sample methods on an empty optional
- 17. Thank You References OCA Oracle Certified Associate Java SE 8 Programmer I Study Guide OCP Oracle Certified Professional Java SE 8 Programmer II Study Guide You may reach piece of codes in the slides on Github page https://github.com/AngelThread/Java8/tree/master/Functional_Programming_in_Java_8 Ugur Yeter [email protected] *Please do not hesitate to contact me if you have any questions related to slides