2. Lambdas in a nutshell
Where and how to use lambdas
The execute around pattern
Functional interfaces, type inference
Method references
Composing lambdas
3. A lambda expression can be understood as a concise
representation of an anonymous function that can be passed
around: it doesn’t have a name, but it has a list of parameters, a
body, a return type, and also possibly a list of exceptions that can
be thrown. That’s one big definition;
let’s break it down:
Anonymous— We say anonymous because it doesn’t have an
explicit name like a method would
normally have: less to write and think about!
Function— We say function because a lambda isn’t associated
with a particular class like a method is.
But like a method, a lambda has a list of parameters, a body, a
return type, and a possible list of
exceptions that can be thrown.
Passed around— A lambda expression can be passed as argument
to a method or stored in a variable.
Concise— You don’t need to write a lot of boilerplate like you do
for anonymous classes.
4. Thus, a lambda expression results in a form of
anonymous class.
Lambda expressions are also commonly referred
to as closures.
A functional interface is an interface that
contains one and only one abstract method.
Thus, a functional interface typically represents
a single action.
The standard interface Runnable is a functional
interface because it defines only one method:
run( ).
functional interface defines the target type of a
lambda expression.
functional interface is sometimes referred to as
a SAM type, where SAM stands for Single Abstract
Method.
5. tomatically
For example, the following code in (a) can be
greatly simplified using a lambda expression
in (b) in three lines.
9. Using lambda expressions, the code is shorter and cleaner. As seen in
this example, lambda expressions may have many variations. You can
handle events by defining handler classes using inner classes,
anonymous inner classes, or lambda expressions. We recommend that
you use lambda expressions because it produces a shorter, clearer, and
cleaner code.
Questions:
1. What is a lambda expression? What is the benefit of using lambda
expressions ? What is the syntax of a lambda expression?
2. What is a functional interface? Why is a functional interface required
for a lambda expression?
11. Oracle Nashorn: A Next-Generation
JavaScript Engine for the JVM by Julien
Ponge
Nashorn is a JavaScript engine. It is used to
execute JavaScript code dynamically at JVM
(Java Virtual Machine). Java provides a
command-line tool jjs which is used to
execute JavaScript code.
You can execute JavaScript code by two
ways:
Using jjs command-line tool, and
By embedding into Java source code.
12. Following is the step by step process to
execute JavaScript code at the JVM.
1. Create a file hello.js.
2. Write and save the following code into the file.
(hello.js)
14. You can execute JavaScript file directly from
your Java file. In the following code, we are
reading a file hello.js with the help of
FileReader class.
16. java.util.Date class
java.sql.Date class
java.util.Calendar class
java.util.GregorianCalendar class
java.util.TimeZone class
java.sql.Time class
java.sql.Timestamp class
Formatting Date and Time
java.text.DateFormat class
java.text.SimpleDateFormat class
17. java.time.LocalDate class
java.time.LocalTime class
java.time.LocalDateTime class
java.time.MonthDay class
java.time.OffsetTime class
java.time.OffsetDateTime class
java.time.Clock class
java.time.ZonedDateTime class
java.time.ZoneId class
java.time.ZoneOffset class
java.time.Year class
java.time.YearMonth class
java.time.Period class
java.time.Duration class
java.time.Instant class
java.time.DayOfWeek enum
java.time.Month enum
19. Java provides a new additional package in Java 8
called java.util.stream. This package consists of
classes, interfaces and enum to allows
functional-style operations on the elements. You
can use stream by importing java.util.stream
package.
You can use stream to filter, collect, print, and
convert from one data structure to other etc. In
the following examples, we have apply various
operations with the help of stream.
Here, we are filtering data by using stream. You
can see that code is optimized and maintained.
Stream provides fast execution.
