* Lambda * Method Reference * Stream API

1. Lambda, Method References &
Aggregate Operations
Md. Fasihul Kabir
Software Engineer, Platform Dhaka, Escenic Asia Ltd.

2. Some Cool Features of Java 8
Lambda expressions
Method references
Default Methods (Defender methods)
A new Stream API
Optional
A new Date/Time API
Nashorn, the new JavaScript engine
Removal of the Permanent Generation
and more…

3. Some Cool Features of Java 8
Lambda Expressions
Method References
Default Methods (Defender methods)
A new Stream API
Optional
A new Date/Time API
Nashorn, the new JavaScript engine
Removal of the Permanent Generation
and more…

4. Lambda Expressions

5. Syntax
(arguments) - {body}

6. Example
button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent event){
System.out.println(button clicked);
}
});

7. button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent event){
System.out.println(button clicked);
}
});

8. button.addActionListener(
event - System.out.println(button clicked)
);

9. Structure of Lambda Expressions
A lambda expression can have zero, one or more parameters
The type of the parameters can be explicitly declared or it can be inferred from the
context.
e.g. (int a) is same as just (a)
Parameters are enclosed in parentheses and separated by commas.
e.g. (a, b) or (int a, int b) or (String a, int b, float c)
Empty parentheses are used to represent an empty set of parameters.
e.g. () - 42
When there is a single parameter, if its type is inferred, it is not mandatory to use
parentheses
e.g. a - return a*a
The body of the lambda expressions can contain zero, one or more statements
If body of lambda expression has single statement curly brackets are not mandatory and
the return type of the anonymous function is the same as that of the body expression
When there is more than one statement in body than these must be enclosed in curly
brackets (a code block) and the return type of the anonymous function is the same as
the type of the value returned within the code block, or void if nothing is returned

10. Method References

16. Kinds of Method References
Kind Example
Reference to a static method ContainingClass::staticMethodName
Reference to an instance method of a
particular object
containingObject::instanceMethodName
Reference to an instance method of an
arbitrary object of a particular type
ContainingType::methodName
Reference to a constructor ClassName::new

17. Reference to a Static Method
The method reference Person::compareByAge is a
reference to a static method.

18. Reference to an Instance Method of a
Particular Object

19. Reference to an Instance Method of an
Arbitrary Object of a Particular Type

20. Reference to a Constructor

23. Aggregate Operations

27. Pipelines and Streams

28. Components of Pipeline
A source: This could be a collection, an array, a
generator function, or an I/O channel. In this example,
the source is the collection roster.
Zero or more intermediate operations. An intermediate
operation, such as filter, produces a new stream.
A terminal operation. A terminal operation, such as
forEach, produces a non-stream result, such as a
primitive value (like a double value), a collection, or in
the case of forEach, no value at all.