Talk on "Eclipse and Java 8" at Eclipse Day India (Bangalore) 2013.

1. © 2013 IBM Corporation | Eclipse and Java 8
1
ECLIPSE AND JAVATM 8
Noopur Gupta
Eclipse JDT/UI Committer
IBM Software lab
noopur_gupta@in.ibm.com

2. © 2013 IBM Corporation | Eclipse and Java 8
2

3. © 2013 IBM Corporation | Eclipse and Java 8
3

4. © 2013 IBM Corporation | Eclipse and Java 8
4
Project Lambda
Functional Interfaces
Old content, new name!
Interfaces that define a single abstract method
(excluding Object methods), are now called as
Functional Interfaces.
Examples: Common callback interfaces like
Runnable and Comparator.
Optionally capture the design intent with the
@FunctionalInterface annotation.

5. © 2013 IBM Corporation | Eclipse and Java 8
5
Project Lambda
Functional Interfaces

6. © 2013 IBM Corporation | Eclipse and Java 8
6
Problem:
“Tiny” anonymous classes.
Used in callbacks, runnables, event handlers,
comparators etc.
All we need!
Project Lambda
Lambda Expressions

7. © 2013 IBM Corporation | Eclipse and Java 8
7
Solution:
Lambda Expression!
Project Lambda
Lambda Expressions
A lambda expression is used to implement a functional interface,
without creating a class or an anonymous class.
Reduced runtime overhead compared to anonymous classes!
VM and JRE optimizations in lambda meta factory.
Method invocation with invokedynamic bytecode instruction.

8. © 2013 IBM Corporation | Eclipse and Java 8
8
Project Lambda
Lambda Expressions
Syntax: (formal parameter list) -> { expression or statements }
Syntax variants:
Concise syntax
compared to
anonymous classes !

9. © 2013 IBM Corporation | Eclipse and Java 8
9
Project Lambda
Lambda Expressions
Target type of a lambda expression must be a functional interface.
Target type is inferred from the surrounding context.
Lambda parameters' types can be inferred.
A lambda is a method without a name and without an identity (no 'this').
Lambda Expressions do not define a new level of scope (just like for loops
and catch clauses).

10. © 2013 IBM Corporation | Eclipse and Java 8
10
Project Lambda
Lambda Expressions
Lambda Expressions can capture (reference) local variables of
enclosing contexts if the local variables are final or effectively final
(if its initial value is never changed).
Beneficial for memory management:
Inner class instances always hold a strong reference to their
enclosing instance can lead to memory leaks.
Lambda expressions that do not capture members from the
enclosing instance do not hold a reference to it !

11. © 2013 IBM Corporation | Eclipse and Java 8
11
Project Lambda
Method References
Problem:
A lambda expression that just invokes a named method – has to provide a
method body.
Solution:
A shorthand for lambda – method reference of the existing named method.

12. © 2013 IBM Corporation | Eclipse and Java 8
12
A method reference is used to refer to a method without invoking it.
A constructor reference is used to refer to a constructor without
creating a new instance of the named class or array type.
Project Lambda
Method References
Kinds of method references:
 A static method (ClassName::methName)
 An instance method of a particular object (instanceRef::methName)
 A super method of a particular object (super::methName)
 An instance method of an arbitrary object of a particular type (ClassName::methName)
Kinds of Constructor references:
 A class constructor reference (ClassName::new)
 An array constructor reference (TypeName[]::new)

13. © 2013 IBM Corporation | Eclipse and Java 8
13
Project Lambda
Method References
Example:

14. © 2013 IBM Corporation | Eclipse and Java 8
14
Project Lambda :
Interface Improvements
Default Methods
Problem:
Evolve interfaces without introducing incompatibility with
existing implementations.
 Standard Java libraries need new lambda-friendly methods.
Solution:
Default methods – means of painless API evolution.

15. © 2013 IBM Corporation | Eclipse and Java 8
15
Project Lambda :
Interface Improvements
Static Methods
Problem:
A common scenario – Java libraries having companion
utility classes with static methods.
Solution:
Static methods – allow helper methods specific to an
interface to live with the interface.

16. © 2013 IBM Corporation | Eclipse and Java 8
16

17. © 2013 IBM Corporation | Eclipse and Java 8
17
Type Annotations
Before Java 8 :
Annotations could only be applied to declarations.
As of Java 8 :
Annotations can also be applied anywhere you use a type!
Support improved analysis of Java programs.
Enabler for checker frameworks and static analysis tools
such as Sonar and FindBugs.
Declaration
Annotation
Type Use
Annotation

18. © 2013 IBM Corporation | Eclipse and Java 8
18
Type Annotations
@
Examples:
To declare a non-empty array of English-language strings:
Each non-static method has an implicit formal
parameter, this, which is called the receiver.
In Java 8, it is permitted to explicitly declare the
method receiver as the first formal parameter.
The only purpose of writing the receiver explicitly is to make
it possible to annotate the receiver’s type.

19. © 2013 IBM Corporation | Eclipse and Java 8
19
Type Annotations
Use of a type name as a scoping mechanism is not a type use,
hence cannot be annotated.
Examples:

20. © 2013 IBM Corporation | Eclipse and Java 8
20
Set up Eclipse IDE (unreleased beta impl):
http://wiki.eclipse.org/JDT_Core/Java8#What_to_do_to_set
_up_the_IDE
Java 8 features:
http://openjdk.java.net/projects/jdk8/features
Lambda FAQ: http://www.lambdafaq.org
Trying Out Lambda Expressions in the
Eclipse IDE:
http://www.oracle.com/technetwork/articles/java/lambda-
1984522.html
Type Annotations Specification:
http://types.cs.washington.edu/jsr308/specification/java-
annotation-design.html

21. © 2013 IBM Corporation | Eclipse and Java 8
21