This document discusses Java lambdas and streams. It begins with an introduction to the speaker, Oleg Tsal-Tsalko, and provides an overview of Java 8 streams including their benefits and common operations. It then covers lambda expressions, functional interfaces, and how lambdas and streams have influenced existing Java classes. The document concludes by providing instructions for downloading a test project to practice using lambdas and streams.

1. Lambdas
HOL
Speaker:
Oleg
Tsal-­‐Tsalko(@tsaltsol)

2. About
me
Oleg
Tsal-­‐Tsalko
Lead
So:ware
Engineer
at
EPAM
Systems.
Speaker,
acEve
member
of
Kiev
JUG.
ParEcipate
in
different
educaEonal
iniEaEves
and
JCP/AdoptJSR
programs.

3. Stream
API
-­‐ An
abstracEon
that
supports
bulk
operaEons
over
sequence
of
elements
-­‐ Not
a
data
structure
-­‐ Simple
and
logical
chaining
of
operaEons
-­‐ Lazy
evaluaEon
-­‐ Internal
parallelism
if
required
-­‐ Concept
of
funcEonal
programming
in
Java

4. txns.stream()
Fluent
and
Simple
.filter(t
-­‐>t.getBuyer().getAge()>=65)
.map(Txn::getSeller)
.disEnct()
.sort(comparing(Seller::getName))
.forEach(s
-­‐>
System.out.println(s.getName());

5. How
can
I
get
a
Stream
to
work
with?
• CollecEon.stream()
• IntStream.range()
• Stream.of()
• Arrays.stream()
• BufferedReader.lines()
• CharSequence.chars()
• Pa`ern.splitAsStream()

6. Internal
iteraEon
over
external
Is
there
signifficant
difference?
for
(Item
item
:
items){
process(item);
}
items.forEach(item
-­‐>
process(item));

7. Lambda
expressions
A
lambda
expression
is
an
anonymous
funcEon
–
Has
an
argument
list,
a
return
type,
and
a
body
(Object
o)
-­‐>
o.toString()
–
A
method
reference
is
a
reference
to
an
exisEng
method
Object::toString
–
Lambdas
can
refer
to
(capture)
values
from
the
enclosing
lexical
scope
(Person
p)
-­‐>p.getName().equals(name)
–
Compiler
can
o:en
infer
argument
types
from
context
p
-­‐>
p.getName().equals(name)
–
Can
be
used
whenever/wherever
you
use
anonymous
classes
with
single
method
You
can
now
pass
behavior
as
a
data
between
your
objects

8. Using
lambdas
FileFilter x = new FileFilter() {
public boolean accept(File f) {
return f.canRead();
}
};
FileFilter x = (File f) -> f.canRead();
FileFilter x = File::canRead;

9. What’s
your
type?
Since
Java
doesn’t
have
FuncEon
type
on
it’s
own
Lambda’s
type
evaluated
to
some
FuncEonal
interface:
Runnable
r
=
()
-­‐>
{
doSmth();
};
Callable
c
=
()
-­‐>
calcResult();
Comparator
comp
=
(o1,
o2)
-­‐>
compare(o1,
o2);

10. FuncEonal
interfaces
java.u&l.func&on
Package:
Predicate<T>
Determine
if
the
input
of
type
T
matches
some
criteria
Consumer<T>
Accept
a
single
input
argumentof
type
T,
and
return
no
result
Function<T, R>
Apply
a
funcEon
to
the
input
type
T,
generaEng
a
result
of
type
R
java.u&l.stream
Package:
Collector<T, A, R>
Used
to
collect
stream
of
elements
of
type
T
into
single
result
of
type
R
Collectors
Contains
number
of
predefined
Collectors

11. Influence
on
exisEng
classes?
java.lang.Iterable#forEach()
java.uEl.CollecEon#stream()
java.uEl.CollecEon#parallelStream()
java.uEl.Comparator#comparing(…)
java.uEl.Comparator#thenComparing(…)
java.uEl.Comparator#reverse()
…

13. InstrucEons
• Download
test
project
from
GitHub:
h`ps://github.com/olegts/LambdasHacking
• Import
it
in
your
favorite
IDE
(IDEA*)
with
JDK8.
• Open
single
Exercises
class.
• Fix
as
much
tests
as
you
can
going
one
by
one
removing
@Ignore
annotaEon
and
coding
up
TODOs.

14. Thank
you!
Oleg
Tsal-­‐Tsalko
Email:
oleg.tsalko@gmail.com
Twi`er:
@tsaltsol