Java 8 presentation

JAVA 8
At First Glance
VISION Team - 2015

Agenda
❖ New Features in Java language
➢ Lambda Expression
➢ Functional Interface
➢ Interface’s default and Static Methods
➢ Method References
❖ New Features in Java libraries
➢ Stream API
➢ Date/Time API

Lambda Expression
What is Lambda Expression?

❖ Unnamed block of code (or an unnamed
function) with a list of formal parameters and
a body.
✓ Concise
✓ Anonymous
✓ Function
✓ Passed around
Lambda Expression

Lambda Expression
Why should we care about
Lambda Expression?

Example 1:
Comparator<Person> byAge = new Comparator<Person>(){
public int compare(Person p1, Person p2){
return p1.getAge().compareTo(p2.getAge());
}
};
Lambda Expression
Example 2:
JButton testButton = new JButton("Test Button");
testButton.addActionListener(new ActionListener(){
@Override public void actionPerformed(ActionEvent ae){
System.out.println(“Hello Anonymous inner class");
}
});

Example 1: with lambda
Comparator<Person> byAge =
(Person p1, Person p2) -> p1.getAge().compareTo(p2.getAge());
Lambda Expression
Example 2: with lambda
testButton.addActionListener(e -> System.out.println(“Hello
Lambda"));

Lambda Expression
Lambda Syntax

Lambda Expression
Lambda parameters Lambda body
Arrow
The basic syntax of a lambda is either
(parameters) -> expression
or
(parameters) -> { statements; }

❖ Lambda does not have:
✓ Name
✓ Return type
✓ Throws clause
✓ Type parameters
Lambda Expression

Examples:
1. (String s) -> s.length()
2. (Person p) -> p.getAge() > 20
3. () -> 92
4. (int x, int y) -> x + y
5. (int x, int y) -> {
System.out.println(“Result:”);
System.out.println(x + y);
}
Lambda Expression

Variable scope:
public void printNumber(int x) {
int y = 2;
Runnable r = () -> System.out.println(“Total is:” + (x+y));
new Thread(r).start();
}
Lambda Expression
Free variable: not define in lambda parameters.
Variable scope:
int y = 2;
Runnable r = () ->{System.out.println(“Total is:” + (x+y));
System.out.println(this.toString());};
new Thread(r).start();
}
Not allow:
int y = 2;
Runnable r = () -> {
x++;//compile error
System.out.println(“Total is:” + (x+y))
};
}

Lambda Expression
Where should we use Lambda?

Comparator:
Comparator<Person> byAge =
Collections.sort(personList, byAge);
Lambda Expression
Listener:
ActionListener listener = e -> System.out.println(“Hello
Lambda")
testButton.addActionListener(listener );
Example:
public void main(String[] args){
(int x, int y) -> System.out.println(x + y);
}

Runnable:
// Anonymous class
Runnable r1 = new Runnable(){
@Override
public void run(){
System.out.println("Hello world one!");
}
};
// Lambda Runnable
Runnable r2 = () -> System.out.println("Hello world two!");
Lambda Expression

Iterator:
List<String> features = Arrays.asList("Lambdas", "Default
Method", "Stream API", "Date and Time API");
//Prior to Java 8 :
for (String feature : features) {
System.out.println(feature);
}
//In Java 8:
Consumer<String> con = n -> System.out.println(n)
features.forEach(con);
Lambda Expression

What is functional interface?
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Functional Interface

● New term of Java 8
● A functional interface is an interface with
only one abstract method.
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● Methods from the Object class don’t
count.
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Annotation in Functional
Interface
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● A functional interface can be annotated.
● It’s optional.
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● Show compile error when define more
than one abstract method.
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Functional Interfaces
Toolbox
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● Brand new java.util.function package.
● Rich set of function interfaces.
● 4 categories:
o Supplier
o Consumer
o Predicate
o Function
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● Accept an object and return nothing.
● Can be implemented by lambda
expression.
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Consumer Interface

Interface Default and Static
Methods
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Interface Default and Static Methods

static <T> Collection<T>
synchronizedCollection(Collection<T
● Advantages:
- No longer need to provide your own companion utility classes. Instead, you
can place static methods in the appropriate interfaces
- Adding methods to an interface without breaking the existing
implementation
java.util.Collections
java.util.Collection
● Extends interface declarations with two new concepts:
- Default methods
- Static methods

[modifier] default | static returnType nameOfMethod (Parameter List) {
// method body
}
● Syntax

Default methods
● 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
● Solve the conflict when the same method declare 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 overriding that
method.

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

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

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

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

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

Method References
● Method references as Lambdas Expressions
Syntax Example As Lambda
ClassName::new String::new () -> new String()
Class::staticMethodName String::valueOf (s) -> String.valueOf(s)
object::instanceMethodName x::toString () -> "hello".toString()
Class::instanceMethodName String::toString (s) -> s.toString()

What is a Stream?
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Stream

Old Java:
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Stream

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Stream
Java 8:

❏Not store data
❏Designed for processing data
❏Not reusable
❏Can easily be outputted as arrays or
lists
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Stream

1. Build a stream
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Stream - How to use
2. Transform stream
3. Collect result

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

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

Intermediate operations (return Stream)
❖ filter()
❖ map()
❖ sorted()
❖ ….
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Stream - Operations

// get even numbers
Stream<Integer> evenNumbers = stream
.filter(i -> i%2 == 0);
// Now evenNumbers have {2, 4, 6, 8}
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Stream - filter()

Terminal operations
❖ forEach()
❖ collect()
❖ match()
❖ ….
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Stream - Operations

// get even numbers
evenNumbers.forEach(i ->
System.out.println(i));
/* Console output
* 2
* 4
* 6
* 8
*/
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Stream - forEach()

Converting stream to list
List<Integer> numbers =
evenNumbers.collect(Collectors.toList());
Converting stream to array
Integer[] numbers =
evenNumbers.toArray(Integer[]::new);
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Stream - Converting to collections

What’s new in Date/Time?
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Date / Time

● Why do we need a new Date/Time API?
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Date / Time
○ Objects are not immutable
○ Naming
○ Months are zero-based

● LocalDate
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Date / Time
○ A LocalDate is a date, with a year,
month, and day of the month
LocalDate today = LocalDate.now();
LocalDate christmas2015 = LocalDate.of(2015, 12, 25);
LocalDate christmas2015 = LocalDate.of(2015,
Month.DECEMBER, 25);

Java 7:
Calendar c = Calendar.getInstance();
c.add(Calendar.DATE, 1);
Date dt = c.getTime();
Java 8:
LocalDate tomorrow = LocalDate.now().plusDay(1);
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Date / Time

● Temporal adjuster
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Date / Time
LocalDate nextPayDay = LocalDate.now()
.with(TemporalAdjusters.lastDayOfMonth());

● Create your own adjuster
TemporalAdjuster NEXT_WORKDAY = w -> {
LocalDate result = (LocalDate) w;
do {
result = result.plusDays(1);
} while (result.getDayOfWeek().getValue() >= 6);
return result;
};
LocalDate backToWork = today.with(NEXT_WORKDAY);
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Date / Time

For further questions, send to us: hcmc-vision@axonactive.vn

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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

Java 8 presentation

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