Java 8 features

Java 8 Features with Examples
Presented By: Gaurav And Ashish

Agenda New Features in Java language
● forEach() method in Iterable interface
● Interface’s default and Static Methods
● Functional Interface
● Lambda Expression
● Method References
New Features in Java libraries
● Stream API
● Date/Time API

For Each() Method in iterable interface
Java 8 has introduced forEach method in java.lang.Iterable interface so
that while writing code we focus on business logic only. forEach method
takes java.util.function.Consumer object as argument, so it helps in
having our business logic at a separate location that we can reuse.
Let’s see forEach usage with simple example.

Example
//creating sample Collection
List<Integer> myList = new ArrayList<Integer>();
for(int i=0; i<10; i++) myList.add(i);
//traversing using Iterator
Iterator<Integer> it = myList.iterator();
while(it.hasNext()){
Integer i = it.next();
System.out.println("Iterator Value::"+i);
}
To Be Continued….

//traversing through forEach method of Iterable with anonymous class
myList.forEach(new Consumer<Integer>() {
public void accept(Integer t) {
System.out.println("forEach anonymous class Value::"+t);
}
});
//traversing with Consumer interface implementation
MyConsumer action = new MyConsumer();
myList.forEach(action);
//Consumer implementation that can be reused
class MyConsumer implements Consumer<Integer>{
public void accept(Integer t) {
System.out.println("Consumer impl Value::"+t);
}
}

Default And static methods in Interface
● Interfaces are enhanced to have method with implementation.
● We can use default and static keyword to create interfaces with
method implementation.
forEach method implementation in Iterable interface is:
default void forEach(Consumer<? super T> action) {
Objects.requireNonNull(action);
for (T t : this) {
action.accept(t);
}
}

Default And static methods in Interface
Syntax

Default methods in Interface
● Classes implement interface that contains a default method
○ Not override the default method and will inherit the default method
○ Override the default method similar to other methods we override in subclass.
○ Redeclare default method as abstract, which force subclass to override it.

Default methods in Interface
● Solve the conflict when the same method declared in interface or
class
○ Method of Superclasses, if a superclass provides a concrete
method.
○ If a superinterface provides a default method, and another
interface supplies a method with the same name and parameter
types (default or not), then you must override that method.

Static methods in Interface
● Similar to default methods except that we can’t override them in the
implementation classes

Functional interface
What is functional interface?

● New term of Java 8
● A functional interface is an interface with only one abstract method.

● Methods from the Object class don’t count.

Annotation in Functional
Interface

● A functional interface can be annotated.
● It’s optional.

● Show compile error when define more than one abstract method.

Functional Interfaces
Toolbox

● Brand new java.util.function package.
● Rich set of function interfaces.
● 4 categories:
○ Supplier
○ Consumer
○ Predicate
○ Function

Consumer interface
● Accept an object and return nothing.
● Can be implemented by lambda expression.

Lambda Expression
Lambda Expression are the way through which we can visualize functional programming in the
java object oriented world. Objects are the base of java programming language and we can
never have a function without an Object, that’s why Java language provide support for using
lambda expressions only with functional interfaces.
Since there is only one abstract function in the functional interfaces, there is no confusion in
applying the lambda expression to the method. Lambda Expressions syntax is (argument) ->
(body). Now let’s see how we can write above anonymous Runnable using lambda expression.
Runnable r1 = () -> System.out.println("My Runnable");

Lambda Expression
● Let’s try to understand what is happening in the lambda expression
above.
○ Runnable is a functional interface, that’s why we can use lambda exp
create it’s instance.
○ Since run() method takes no argument, our lambda expression also
argument.
○ Just like if-else blocks, we can avoid curly braces ({}) since we have
statement in the method body. For multiple statements, we would h
braces like any other methods.

Lambda Expression
● A block of code that you can pass around so it can be executed later, once or multiple
times.
● Anonymous methods.
● Reduce verbosity caused by anonymous classes.
● Alonzo Church in his invention of the lambda calculus in 1936. - Lisp 1958 - Supported in
C#, JavaScript,Python, Ruby, C++11

Lambda Expression
Example 1:
Runnable r = new Runnable(){
@Override
public void run() {
System.out.println("My Runnable");
}};
Example 2:
Comparator<Person> byAge = new Comparator<Person>(){
public int compare(Person p1, Person p2){
return p1.getAge().compareTo(p2.getAge());
}
};

Lambda Expression
Example 1: with lambda
Runnable r1 = () -> System.out.println("My Runnable");
Example 2: with lambda
Comparator<Person> byAge =
(Person p1, Person p2) -> p1.getAge().compareTo(p2.getAge());

Examples of Java 8 Lambdas
● A Java 8 lambda is basically a method in Java without a declaration usually written as
(parameters) -> { body }. Examples,
(int x, int y) -> { return x + y; }
x -> x * x
( ) -> x
● A lambda can have zero or more parameters separated by commas and their type can
be explicitly declared or inferred from the context.
● Parenthesis are not needed around a single parameter.
● ( ) is used to denote zero parameters.
● The body can contain zero or more statements.
● Braces are not needed around a single-statement body.

Print a list of integers with a lambda
List<Integer> intSeq = Arrays.asList(1,2,3);
intSeq.forEach(x -> System.out.println(x));
•x -> System.out.println(x) is a lambda expression that defines an
anonymous function with one parameter named x of type Integer

A multiline lambda
intSeq.forEach(x -> {
x += 2;
System.out.println(x);
});
•Braces are needed to enclose a multiline body in a lambda
expression.

A lambda with a defined local variable
intSeq.forEach(x -> {
int y = x * 2;
System.out.println(y);
});
•Just as with ordinary functions, you can define local variables inside
the body of a lambda expression

A lambda with a declared parameter type
intSeq.forEach((Integer x -> {
x += 2;
System.out.println(x);
});
•You can, if you wish, specify the parameter type.

A lambda with a declared parameter type
public class LVCExample {
public static void main(String[] args) {
int var = 10;
intSeq.forEach(x -> System.out.println(x + var));
}
}
local variables used inside the body of a lambda must be final or
effectively final

Method Reference
● Method reference is an important feature related to lambda expressions. In order to that a
method reference requires a target type context that consists of a compatible functional
interface.

Method Reference
● There are four kinds of method references:
○ Reference to a static method
○ Reference to an instance method of a particular object
○ Reference to an instance method of an arbitrary object of a particular type
○ Reference to a constructor

Method Reference
● Reference to a static method
The syntax: ContainingClass::staticMethodName

Method Reference
● Reference to an instance method of a particular object
The syntax: containingObject::instanceMethodName

Method Reference
● Reference to an instance method of an arbitrary object of a particular
type.
The syntax: ContainingType::methodName

Method Reference
● Reference to a constructor
The syntax: ClassName::new

Method Reference
● Method references as Lambdas Expressions

Stream
Before we look into Java Stream API Examples, let’s see why it was
required. Suppose we want to iterate over a list of integers and find out
sum of all the integers greater than 10.
Prior to Java 8, the approach to do it would be:
private static int sumIterator(List<Integer> list) {
Iterator<Integer> it = list.iterator();
int sum = 0;
while (it.hasNext()) {
int num = it.next();
if (num > 10) {
sum += num;
}
}
return sum;
}

Stream
There are three major problems with the previous approach:
1. We just want to know the sum of integers but we would also have
to provide how the iteration will take place, this is also called
external iteration because client program is handling the algorithm
to iterate over the list.
2. The program is sequential in nature, there is no way we can do
this in parallel easily.
3. There is a lot of code to do even a simple task.

Stream
1. To overcome all the above shortcomings, Java 8 Stream API was introduced. We can use
Java Stream API to implement internal iteration, that is better because java framework is
in control of the iteration.
2. Internal iteration provides several features such as sequential and parallel execution,
filtering based on the given criteria, mapping etc.
3. Most of the Java 8 Stream API method arguments are functional interfaces, so lambda
expressions work very well with them. Let’s see how can we write above logic in a single
line statement using Java Streams.
private static int sumStream(List<Integer> list) {
return list.stream().filter(i -> i > 10).mapToInt(i -> i).sum();
}

What exactly is Stream ?
“A sequence of elements from a source that supports data processing
operations”
● Sequence of elements— Collections are data structures, they’re mostly about storing
and accessing elements with specific time/space complexities. But streams are about
expressing computations such as filter, sorted, and map. Collections are about data;
streams are about computations.
● Source— Streams consume from a data-providing source such as collections, arrays, or
I/O resources. Note that generating a stream from an ordered collection preserves the
ordering. The elements of a stream coming from a list will have the same order as the list.
● Data processing operations— Streams support database-like operations and common
operations from functional programming languages to manipulate data, such as filter,
map, reduce, find, match, sort, and so on. Stream operations can be executed either
sequentially or in parallel

Collections and java Stream
● Java Stream is a data structure that is computed on-demand.
● Java Stream doesn’t store data,.
● Can easily be outputted as arrays or lists
● Java Stream operations use functional interfaces.
● Java 8 Stream internal iteration principle helps in achieving
lazy-seeking in some of the stream operations.
● Java Streams are consumable.
● Java 8 Stream support sequential as well as parallel processing,

Stream-Build Streams
● Build streams from collections
List<Dish> dishes = new ArrayList<Dish>();
....(add some Dishes)....
Stream<Dish> stream = dishes.stream();

Stream-Build Streams
● Build streams from arrays
Integer[] integers =
{1, 2, 3, 4, 5, 6, 7, 8, 9};
Stream<Integer> stream = Stream.of(integers);

Function Package In Java 8
● Function package contains Functional interfaces.
● Some of the main functional interfaces are :-
○ Function interface
○ Predicate interface
○ Consumer interface
○ Supplier interface

Function And BiFunction interface
● Function represents a function that takes one type of argument and returns another
type of argument. Function<T, R> is the generic form where T is the type of the input
to the function and R is the type of the result of the function.
● For handling primitive types, there are specific Function interfaces – ToIntFunction,
ToLongFunction, ToDoubleFunction, ToIntBiFunction, ToLongBiFunction,
ToDoubleBiFunction, LongToIntFunction, LongToDoubleFunction, IntToLongFunction,
IntToDoubleFunction etc.
● We can apply our business logic with that value and return the result. Function has
function method as apply(T t) which accepts one argument.
import java.util.function.Function;
public class FunctionDemo {
Function<Integer, String> function = (num1) -> "Result is: ” + num1;
System.out.println(function.apply(20));
}
}

Function And BiFunction interface
● Some of the Stream methods where Function or it’s primitive specialization is used are:
○ <R> Stream<R> map(Function<? super T, ? extends R> mapper)
○ IntStream mapToInt(ToIntFunction<? super T> mapper) – similarly
double returning primitive specific stream.
○ IntStream flatMapToInt(Function<? super T, ? extends IntStream> m
similarly for long and double
○ <A> A[] toArray(IntFunction<A[]> generator)
○ <U> U reduce(U identity, BiFunction<U, ? super T, U> accumulator,
BinaryOperator<U> combiner)

Predicate And BiPredicate Interface
● It represents a predicate against which elements of the stream are tested. This is used
to filter elements from the java stream.
● Just like Function, there are primitive specific interfaces for int, long and double.
● Predicate functional method is test(Object). Find the simple example for how to use
Predicate.
public class BiPredicateDemo {
public static void main(String[] args){
BiPredicate<Integer, String> condition = (i,s)-> i>20 && s.startsWith("R");
System.out.println(condition.test(10,"Ram"));
System.out.println(condition.test(30,"Shyam"));
System.out.println(condition.test(30,"Ram"));
}
}

Predicate And BiPredicate Interface
● Some of the Stream methods where Predicate or BiPredicate specializations are used
are:
○ Stream<T> filter(Predicate<? super T> predicate)
○ boolean anyMatch(Predicate<? super T> predicate)
○ boolean allMatch(Predicate<? super T> predicate)
○ boolean noneMatch(Predicate<? super T> predicate)

Consumer And BiConsumer Interface
● It represents an operation that accepts a single input argument and returns no result.
● It can be used to perform some action on all the elements of the java stream.
● Consumer functional method is accept(Object, Object). This methods performs the
operation defined by BiConsumer.
public class ConsumerExample {
static void print(String name){
System.out.println("Hello "+name);
}
}
// Referring method to String type Consumer interface
Consumer<String>consumer1=ConsumerExample::print;
consumer1.accept("John");

Consumer And BiConsumer Interface
● Some of the Java 8 Stream methods where Consumer, BiConsumer or it’s primitive
specialization interfaces are used are
○ Stream<T> peek(Consumer<? super T> action)
○ void forEach(Consumer<? super T> action)
○ void forEachOrdered(Consumer<? super T> action)

Supplier Interface
● Supplier represent an operation through which we can generate new values in the
stream.
● A supplier of objects. The result objects are either created during the invocation of
get() or by some prior action..
● And the sole method in this interface is get() which should return an object of the
declared type
public class Person {
private String name;
public Person(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
public class TestSupplier {
Supplier < Person > supplier = () - > {
return new Person("Varun");
};
Person p = supplier.get();
System.out.println("Person Detail:n" +
p.getName());
}
}

Supplier Interface
● Some of the methods in Stream that takes Supplier argument are:
○ public static<T> Stream<T> generate(Supplier<T> s)
○ <R> R collect(Supplier<R> supplier,BiConsumer<R, ? super T>
accumulator,BiConsumer<R, R> combiner)

Stream-java.util.optional
● Java Optional is 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. Stream
terminal operations return Optional object. Some of these methods are:
○ Optional<T> reduce(BinaryOperator<T> accumulator)
○ Optional<T> min(Comparator<? super T> comparator)
○ Optional<T> max(Comparator<? super T> comparator)
○ Optional<T> findFirst()
○ Optional<T> findAny()

Stream-operations
● Intermediate operations (return Stream)
Java Stream API operations that returns a new Stream are called intermediate
operations. Most of the times, these operations are lazy in nature, so they start
producing new stream elements and send it to the next operation. Intermediate
operations are never the final result producing operations. Commonly used
intermediate operations are filter and map.

Stream-operations
● Terminal operations
Java 8 Stream API operations that returns a result or produce a side effect. Once the
terminal method is called on a stream, it consumes the stream and after that we
can’t use stream. Terminal operations are eager in nature i.e they process all the
elements in the stream before returning the result. Commonly used terminal
methods are forEach, toArray, min, max, findFirst, anyMatch, allMatch etc. You can
identify terminal methods from the return type, they will never return a Stream.

Stream-operations
● Short circuiting operations
An intermediate operation is called short circuiting, if it may produce finite stream for an
infinite stream. For example limit() and skip() are two short circuiting intermediate operations.
A terminal operation is called short circuiting, if it may terminate in finite time for infinite
stream. For example anyMatch, allMatch, noneMatch, findFirst and findAny are short circuiting
terminal operations.

Date ANd Time API
Why do we need new Java Date Time API?
1. Java Date Time classes are not defined consistently, we have Date Class in both java.util as well as
java.sql packages. Again formatting and parsing classes are defined in java.text package.
2. java.util.Date contains both date and time, whereas java.sql.Date contains only date. Having this in
java.sql package doesn’t make sense. Also both the classes have same name, that is a very bad design
itself.
3. There are no clearly defined classes for time, timestamp, formatting and parsing. We have
java.text.DateFormat abstract class for parsing and formatting need. Usually SimpleDateFormat class is
used for parsing and formatting.
4. All the Date classes are mutable, so they are not thread safe. It’s one of the biggest problem with Java
Date and Calendar classes.
5. Date class doesn’t provide internationalization, there is no timezone support. So java.util.Calendar and
java.util.TimeZone classes were introduced, but they also have all the problems listed above.

Date ANd Time API
Java 8 Date Time API is JSR-310 implementation. It is designed to overcome all the flaws in the
legacy date time implementations. Some of the design principles of new Date Time API are:
1. Immutability: All the classes in the new Date Time API are immutable and good for multithreaded
environments.
2. Separation of Concerns: The new API separates clearly between human readable date time and
machine time (unix timestamp). It defines separate classes for Date, Time, DateTime, Timestamp,
Timezone etc.
3. Clarity: The methods are clearly defined and perform the same action in all the classes. For example,
to get the current instance we have now() method. There are format() and parse() methods defined in
all these classes rather than having a separate class for them.
4. Utility operations: All the new Date Time API classes comes with methods to perform common tasks,
such as plus, minus, format, parsing, getting separate part in date/time etc.
5. Extendable: The new Date Time API works on ISO-8601 calendar system but we can use it with other
non ISO calendars as well.

Java 8 Date ANd Time Packages
Java 8 Date Time API consists of following packages.
1. java.time Package: This is the base package of new Java Date Time API. such as
LocalDate, LocalTime, LocalDateTime, Instant, Period, Duration etc. All of these classes
are immutable and thread safe.
2. java.time.chrono Package: This package defines generic APIs for non ISO calendar
systems. We can extend AbstractChronology class to create our own calendar system.
3. java.time.temporal Package: This package contains temporal objects and we can use it
for find out specific date or time related to date/time object. For example, we can use
these to find out the first or last day of the month. You can identify these methods easily
because they always have format “withXXX”.
4. java.time.zone Package: This package contains classes for supporting different time
zones and their rules.

References
❖ Java Platform Standard Edition 8 Documentation,
(http://docs.oracle.com/javase/8/docs/)
❖ Java 8 In Action, Raoul-Gabriel Urma, Mario Fusco, and Alan Mycroft.
❖ Beginning Java 8 Language Features, Kishori Sharan.
❖ What’s new in Java 8 - Pluralsight
❖ http://www.journaldev.com/2389/java-8-features-with-examples

Sample Implementation
git@github.com:NexThoughts/java8.git

Java 8 features

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Java 8 features