5-Optional class <br>

6-forEach

Interface New feature (default & static method)

both above method can use to extends the interface function without effecting of implement class.

1-method definition allowed with default keyword

its same as instance method of class we use default keyword as modifier of method.

Example:

default String helloDefaultInInterface() {

return "default";

}

2-method definition allowed with static keyword

Example:

static String helloStaticMethodInInterface() {

return "staticMethodInInterface";

}

Note: before to java-8 we used only public,abstract,strictfp keywords.

now after java-8 two keywords added to used --default, static

if you used any others keyword you will get following error.

"Illegal modifier for the interface method helloStaticMethodInInterface; only public, abstract, default, static and strictfp are permitted"

strictfp

strictfp keywords can use as method modifier or class or interface. only abstract method cant use this.

it used to calculate same floating point result irrespective to platform processors.(16bit/32bit/64bit )

strictfp ---> strict to floating point as result irrespective to machine processors(16bit/32bit/64bit )

Functional Interface

The interface which have only one(not zero or more than 1) abstract method is called functional interface.

we can use class level annotation to specify interface as functional.

example:

@FunctionalInterface

public interface Greeting {

void greet();

}

basically functional interface normally used in lamdaexpression(functional programming).

LamdaExpression:

lambda expression is syntactic sugar or shortest way of implementation of functional interface.

in place of lambda expression we can use anonymous classes.

How to write LamdaExpression

before learning Lamda we have to learn method reference operator (::) double colon.

There are four way to use method reference(::)

1) static method using class ....Math::max ---equivalent to Math.max(x,y)

2) instance method using object ....System.out::println ---equivalent to System.out.println(x)

3) instance method using class ....String.length ----equivalent to str.length()

4) constructor using new .... ArrayList::new ----equivalent to new ArrayList()

Note: argument or object value like x,y,str will be provided by Lamda-expression api automatically.

General Syntax:

FunctionalInterface ref = (arugement)-> {body}

(argument)-> {body} is called lamda expression--its way to provide implementation of FunctionalInterface.

if method having one only argument then it cal also write in following form

argument -> {body}

Method reference statement also known as one type of lamda expression.

FunctionalInterface ref = Method reference statement

Example:

1)using method body

Greeting greet1 = ()->System.out.println("LambdaExpression");

2) using method reference statement here findMyAge is static method of Greeting Interface

Greeting greet2 = Greeting::findMyAge

Stream Api

Now java collection can used as stream of object using stream api to improve performance.

Need to learn

1) foreach method

2) Stream object

3) built-in functional interface. (Function,Predicate)

4)Convert Regex to Predicate

//using collections

List<String> names = Arrays.asList("amir","meer","java","c++");

names.forEach(System.out::println);

Consumer<String> cons = name-> System.out.println(name.toUpperCase());

names.forEach(cons);

//ways to create streams...

//1) using stream() method of collection. stream is default method of Collection Interface

Stream<String> nameStreams = names.stream();

nameStreams.forEach(cons);

///2) using Stream.of methods

Stream<Integer> stream = Stream.of(1,2,3,4,5,6,7,8,9);

stream.forEach(System.out::println);

//Predicate Interface

//its used to send test/validate someinput...

Predicate<String> pre = name -> {return name.contains("A");};

System.out.println(pre.test("Amir"));

System.out.println(pre.test("amir"));

//convert RegEx to Predicate

Predicate<String> emailFilter = Pattern.compile("^(.+)@example.com$").asPredicate();

System.out.println("regex-"+ emailFilter.test("a@example.com"));

//Function Interface

//it use to process some input and return some output based on apply logic.

Function<String,String> worker = (input) -> {return input.toLowerCase();};

System.out.println(worker.apply("Amir Rizvi"));

//Optional class....

//its solution for NullPointerException

String name = "Amir";

String name2 = null;

if (Optional.ofNullable(name).isPresent()) {

System.out.println("Present-"+name);

}

if (Optional.ofNullable(name2).isPresent()) {

System.out.println("Not-Present-"+name2);

}

Joda Date api

// There 4 classes for date conversion (String to Date object)

//1) LocalDate.parse() 2) LocalDateTime.parse() 3)DateTimeFormatter.ofPattern(),LocalTime

//default date format for joda api is known as -ISO8601 date pattern

//default date format for joda api is - "2019-08-07";

//default DateTime format for joda api is "2016-04-04T11:50"

String dateOnly = "2019-08-06";

LocalDate date = LocalDate.parse(dateOnly);

System.out.println(date.isBefore(LocalDate.now()));

System.out.println(LocalDate.now()); //2019-08-07

System.out.println(LocalTime.now()); //21:37:11.611

System.out.println(LocalDateTime.now()); //2019-08-07T21:37:11.612

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyyddMM");

LocalDate parseDate = LocalDate.parse("20191011", formatter);

System.out.println(parseDate); //2019-11-10