Java 8 고급 (6/6)

Java 엿새째
TmaxSoft R&D Center
1
113년 10월 22일 화

자바 교육 계획
1일 : Language, String,
ClassLoader, Proxy
2일 : GC, Collections
3일 : Thread, Java Memory
Model
4일 : AQS, ForkJoin,
Concurrent Utils
5일 : IO, Generics, Annotation,
RMI
6일 : Unsafe, Lambda (Java 8)
2
내겐 바스켓만 보여 (Flow 상태)
213년 10월 22일 화

오늘 내용
sun.misc.Unsafe
Lambda (Java 8)
3
313년 10월 22일 화

sun.misc.Unsafe
4
413년 10월 22일 화

sun.misc.Unsafe
5
A collection of methods for performing low-level, unsafe operations
park, unpark
direct memory manipulation
provide wrappers for malloc, realloc, free, memset, memcpy
(not Java Heap)
direct object memory manipulation
CAS operations : compareAndSwap
deﬁneClass, deﬁneAnonymousClass
513년 10월 22일 화

Java is not safe with Unsafe
6
can easily corrupt memory
fast serialization
super array (non-Java heap)
allocateMemory(long size)
can cause JVM crash
613년 10월 22일 화

Lambda
7
The
issue
being
debated
is
not
whether
closures
are
a

good
idea
-‐
because
they
clearly
are
-‐
but
whether

the
beneﬁts
of
retroﬁ7ng
the
Java
language
with

closures
are
worth
the
costs.
-‐
Brian
Goetz
713년 10월 22일 화

Functional Programming
8
lambda
anonymous function with a single argument
closure
a block of code that may contain free (unbound)
variables
currying
handling multiple argument function with lambda
function
813년 10월 22일 화

Java 8 Lambda Expression
SAM (single abstract method) of an interface
Java lambda expression
a list of formal parameters and a body—an expression
or block—expressed in terms of those parameters
e.g,
s -> s.toUpperCase()
(int a, int b) -> a + b
9
913년 10월 22일 화

Method Reference expression
method reference : refer to a method without invoking it
System::getProperty
"abc"::length
constructor reference : refer to a constructor without creating
a new instance of the named class or array type
ArrayList::new
int[]::new
e.g, Arrays.sort(myIntegerArray, Integer::compare)
10
1013년 10월 22일 화

Java 8 Closure
For both lambda bodies and inner classes, local
variables in the enclosing context can only be
referenced if they are final or effectively final.
A variable is effectively final if it is never assigned to
after its initialization.
11
1113년 10월 22일 화

Java 8 Currying
Currying :A technique of transforming a multi-argument
function in such a way that it can be called as a chain
of functions, each with a single argument.
12
1213년 10월 22일 화

New Object-oriented feature
mixin
a class which contains a combination of methods
from other classes.
can also be viewed as an interface with implemented
methods.
Mixins encourage code reuse and avoid well-known
pathologies associated with multiple inheritance.
13
1313년 10월 22일 화

Java 8 Default Method
Java’s language addition of mixin-like thing
provides a default implementation for any class that
implements the interface without overriding the
method.
allows new functionality to be added to existing (and
perhaps already widely-distributed) interfaces.
More generally, it provides a mechanism for multiple
inheritance of behavior.
14
1413년 10월 22일 화

Java 8 Changes to Interface
Now, interface method can be default, static and
abstract
all the non-default, non-static methods in the
interface are abstract as before
Default methods of super-interface can be accessed
<InterfaceName>.super.<methodName>()
15
1513년 10월 22일 화

Java 8 Project Lambda
Language Changes
Still, No Function Type
Functional Interface
Default Method
Streams
invokeDynamic
java.util.Spliterator
16
1613년 10월 22일 화

Java Lambda ABC
@interface java.lang.FunctionalInterface
Just a hint for compiler (compile error if does not have
SAM)
any interface which has SAM is functional interface
package java.util.function
lambda function does not create additional classes unlike
anonymous inner classes
it creates a private static lambda method
17
1713년 10월 22일 화

Streams
handle aggregate operations DECLARATIVELY
stream pipeline
1 source : collection, array, generator ftn, IO, ...
0 or more intermediate operations : ﬁlter, map, ...
1 terminal operation : forEach, reduce, sum, ...
18
1813년 10월 22일 화

Stages of Streams
txns.stream()
.ﬁlter(txn -> txn.getBuyer().getAge() >= 65)
.map(txn -> txn.getSeller())
.distinct()
.sort(comparing(seller -> seller.getName()))
.forEach(seller ->
System.out.println(seller.getName());
19
source
intermediate
intermediate
intermediate
intermediate
terminal
intermediate ops just setup pipeline
and returns new stream
1913년 10월 22일 화

Parallel Streams
A stream pipeline can be created with an orientation of either
serial or parallel
Parallelism may be faster but introduces non-determinism
Internally uses fork-join framework
Collection c = ...;
List r1 = c.stream().map(...).collect(toList());
List r2 = c.parallelStream().map(...).collect(toList());
20
2013년 10월 22일 화

Parallel Streams
21
2113년 10월 22일 화

MethodHandle
java.lang.invoke 패키지
can store references to methods in the constant pool, load
with LDC (load constant)
can obtain a method handle for any method (or ﬁeld access)
But
MethodHandle invocation performance is not good
Lambda is language level method, MethodHandle is VM
level method
22
2213년 10월 22일 화

Lambda Invocation
desugar implementation method
private static boolean lambda$1(int minAge, Person p) { ... }
lambda metafactory에 MethodHandle argument로 전달
invokeDynamic 호출
Predicate $p = invokedynamic[bootstrap=LambdaMetaFactory, ... ]
moving more work from static compiler to runtime
performance
linkage, capture 비용은 inner class보다 싸지만 invoke 비용은 비싸다!
23
2313년 10월 22일 화

invokeDynamic
invokeStatic
System.currentTimeMillis(), Math.log(1.0)
invokeVirtual
"hello".toUpperCase(), System.out.println()
invokeInterface
myList.add("happy happy"), myRunnable.run()
invokeSpecial (constructor or super call)
new ArrayList(), super.equals(other)
성능 비교
invokeStatic (2.7배) >> invokeDynamic (12.6배) >> reﬂection
24
2413년 10월 22일 화

다음 시간 예정
JEUS Web Engine
25
여러분의 전성시대는 언제였나요?
2513년 10월 22일 화

Java 8 고급 (6/6)

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