Java8 Lambda and Streams

Introduction of Java8
Lambda Expression
Presenter: Prem Chand Mali, Mindfire Solutions
Date: 19/06/2014

About Me
SCJP/OCJP - Oracle Certified Java Programmer
MCP:70-480 - Specialist certification in HTML5
with JavaScript and CSS3 Exam
Skills : Java, Swings, Springs,
Hibernate, JavaFX, Jquery,
prototypeJS, ExtJS.
Connect Me :
https://www.facebook.com/prem.c.mali
http://www.linkedin.com/in/premmali
https://twitter.com/prem_mali
https://plus.google.com/106150245941317924019/about/p/pub
Contact Me :
premchandm@mindfiresolutions.com / prem.c.mali@gmail.com
mfsi_premchandm

Agenda
History
What is Lambada ?
Syntax
Function Interface
Default Methods
Variable capture
Method References
Q & A

History
• Lambda calculus (also written as λ-calculus) is a formal system in mathematical
logic and computer science for expressing computation based on function
abstraction and application using variable binding and substitution.
• The lambda calculus was introduced by mathematician Alonzo Church in the 1930s
as part of an investigation into the foundations of mathematics.
• Programming languages ( C#, Javascript, Ruby, C++, etc) have support for lambda
expressions.
• Java 8 have lambda expressions.

What is Lamdba expression ?
• Lambda expressions are anonymous functions.
• Lambda expressions can be assigned to variable, passed to function and it can be
returned from function.

Syntax
() -> { System.out.printlns("Hello World!");}
(int a, int b) -> a + b
() -> { return 1; }
(String name) -> { System.out.println("Hello "+name); }
n -> n % 2 != 0

JDK single method interfaces
public interface Runnable { void run(); }
public interface Callable<V> { V call() throws Exception; }
public interface ActionListener { void actionPerformed(ActionEvent e); }
public interface Comparator<T> { int compare(T o1, T o2); boolean equals(Object
obj); }

Functional Interface
• Functional Interfaces Annotate by @FunctionInterface
• Functional Interfaces which has only one method.
• Functional Interfaces can have one or more default methods.

@FunctionalInterface
Public interface MyDemo {
public void doSomething();
//public void doSomethingForDemo(); Compiler error.
}

Default Methods
• Default method enable you to add new functionality to the interfaces of your
libraries and ensure binary compatibility with code written for older versions of
those interfaces.
• Default key word needs to use to make default method.
• Default method shouldn't be abstract.

Default Methods
public default String myDefault() {
System.out.println(“Hello world from default”);
}
}

Variable Capture
• In Java8 Local variable are accessible from Lambda expressions. In Java7 compiler
complains.
• When you try to modify local variable value compiler will complain if it not final.

Variable Capture
Public Class MyDemo {
public static void main(String[] args) {
String myName = “Runnable”;
Runnable r = () → System.out.println(“ Name : ” + myName);
//myName = “something”;
r.run();
}
}

public default String myDefault() {
System.out.println(“Hello world from default”);
}
}

Method Reference
• Method reference can be use to reuse the existing methods.
• You need to use :: for method reference.
integer.forEach(Example::doSomething);

Question and
Answer

Thank you

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