Software Uni Conf October 2014

Pragmatic: helping you bypass unwanted jobs since 2013

Nayden Gochev
(a.k.a. JOKe)
Superhero with Java powers
EJB
Java
Spring
Android
Hybris
GWT
JSF
RMI
Struts
JAX-RS
JPA
JMS
Hibernate
C#
ASP.NET
TestStudio
JustMock
WCF
MVC
RichFaces EntityFramework
JAX-WS
RadControls
DataAccess
MbUnit WebForms
JavaScript
JustCode
Eclipse
PHP
Objective-C
ExtJS
KendoUI
jQuery UI
jQuery
TFS
Spring MVC
AngularJS

Java 8 hidden bits
Not your grandpa’s Java
Special thanks to
Dmitry Alexandrov
Ivan St. Ivanov

But before that…
The Bulgarian Java User
Group
• http://java-bg.org
• http://groups.google.com/group/bg-jug

So the plan.. the plan …was
• Java 7 … yes 7
• Java 8 (you should know already about lambdas,
stream API so on)
– How this lambdas work ? anonymous class loader, invoke dynamic ?
– Exact Numeric Operations
– Type Annotations
– Optional … or what the hell is this ?
– “New” Date and Time .. another one !?
– Nashorn
But it’s gone :(

The NEW plan is…
• Starting with Java 7 ( 1-3-4 slides )
• Java 8
– Lambdas (what is this ? you saw yesterday right ? hmmm… )
– Default methods on interfaces ? yes it is ugly :(( cry :(
– Static methods on interfaces (whaaat !?!?! Noooo )
– Stream API (nice name isn't it ? ok LINQ is maybe nicer :)
– Optional
– Exact Numeric Operations
– Type Annotations - we “should” have time for this
– Nashorn - I really hope to have time for this … its awesome

But wait wait.. Java ? Rly?
Why should we care?

TIOBE Index for June 2014
Jun 2014 Jun 2013 Change Language Ratings Change
1 1 C 16.191% -1.62%
2 2 Java 16.113% -0.54%
3 3 Objective-C 10.934% +0.58%
4 4 C++ 6.425% -2.39%
5 6 C# 3.944% -1.84%
6 7 (Visual)
Basic
3.736% -0.61%
7 5 PHP 2.848% -3.14%

http://langpop.com/
Google Search Results

PYPL populartY index
• The PYPL PopularitY of Programming Language
Index is created by analyzing how often language
tutorials are searched
Position
June 2014
Position
June 2013
Delta in
position
Programming language Share in
June 2014
Twelve mont
h
trends
1 1 Java 26.9 % -0.1 %
2 2 PHP 13.2 % -1.4 %
3 4 C# 10.3 % +0.2 %
4 3 Python 10.2 % +0.4 %
5 5 C++ 8.4 % -0.9 %
6 6 C 7.9 % -0.2 %
So .. yes… you should care !

But …Java is so old
(~20 years in fact)
• “There are simply no new features in Java,”
• “Java looks like Y language X years ago”
• “C#, Ruby and Python has everything you can dream
of. “
Reading is more important then writing.
be written for humans to read and only incidentally for computes

Java 7
• We all know about diamond operator right?
– List<Integer> primes = new ArrayList<>();
• And Strings in switch
• And Fork Join Framework
• And Underscore in Numeric literals
– int billion = 1_000_000_000; // 10^9
• And maybe catching Multiple Exception Type in Single Catch Block
– catch(ClassNotFoundException|SQLException ex)
• Binary Literals with prefix "0b“
– int binary = 0B0101_0000_1010_0010_1101_0000_1010_0010;
• G1 Garbage Collector
• And we all know about Automatic Resource Management

The biggest two additions to Java 7 are.. ?
1) MethodHandle
Method handles gives us unrestricted capabilities for
calling non-public methods.
Compared to using the Reflection API,
access checking is performed when the method
handle is created as opposed to every time the method is
called.

Reflection example
Class<?>[] argTypes =
new Class[] { int.class, String.class };
Method meth = MethodAccessExampleWithArgs.class.
getDeclaredMethod(
"bar", argTypes);
meth.setAccessible(true);
meth.invoke(instance, 7, "Boba Fett");

MethodHandle example
MethodType desc = MethodType.methodType(
void.class, int.class, String.class);
MethodHandle mh = MethodHandles.lookup().findVirtual(
MethodAccessExampleWithArgs.class, "bar", desc);
mh.invokeExact(mh0, 42, "R2D2");

and the second big thing in
Java 7 is … ?
• 2) invokedynamic
The culmination of invokedynamic is, of course,
the ability to make a dynamic call that the JVM
not only recognizes, but also optimizes in the
same way it optimizes plain old static-typed
calls.

What we all (almost all?) know that before
java 7 there were 4 byte codes for method
invocations
• invokevirtual - Invokes a method on a class.
• invokeinterface - Invokes a method on an interface.
• invokestatic - Invokes a static method on a class.
• invokespecial - Everything else called this way can be
constructors, superclass methods, or private methods.

how invokedynamic look
invokevirtual #4 //Method
java/io/PrintStream.println:(Ljava/lang/String;)V
invokedynamic #10
//NameAndTypelessThan:(Ljava/lang/Object;Ljava/lang/Object;)
But wait. How does the JVM find the method if the receiver type isn't supplied?
When the JVM sees an invokedynamic bytecode, it uses the new linkage
mechanism that I tried to explain yesterday. For more checkout the Brian Goetz
JavaOne speak from 2013

Lambdas
• Lambdas bring anonymous function types in Java
(JSR 335):
(parameters) -> {body}
• Example:
(x,y) -> x + y

Lambdas (2)
• Lambdas can be used in place of functional
interfaces (interfaces with just one method such
as Runnable)
• Example:
new Thread(new Runnable() {
@Override
public void run() {
System.out.println("It runs!");
}
}
).start();
new Thread(() ->
System.out.println("It runs!")
).start();

So what can be used as a
lambda ?
 Every interface with only one method aka @FunctionalInterface
 Examples of such functional interfaces:
java.lang.Runnable -> run()
java.util.concurrent.Callable -> call()
java.security.PrivilegedAction -> run()
java.util.Comparator -> compare(T o1, T o2)
java.awt.event.ActionListener ->
actionPerformed (ActionEvent e)

Some new functional
interfaces
 Additional functional interfaces are provided by the
java.util.function package for use by lambdas such as:
o Predicate<T> - one method with param of type T and
boolean return type
o Consumer<T> - one method with param T and no return type
o Function<T, R> - one method with param T and return type R
o Supplier<T> - one method with no params and
return type T

Default methods
 Default aka extension methods provide a mechanism for
extending an existing interface without breaking
backward compatibility
public interface Iterable<T> {
default void forEach(Consumer<? super T> action) {
Objects.requireNonNull(action);
for (T t : this) {
action.accept(t);
}
}
}

Static methods on interfaces
 You can declare static methods on interfaces:
public interface ContentFormatter {
public void format();
static String convertRegex(String
regex) {
...
}
}
 None of the implementing classes will have this
method available to them
 The idea : less utility classes..

Notes about
@FuncitonalInterfaces
@FunctionalInterface
interface Test2 {
public default void doSomething() {}
}
This is NOT a functional interface and cannot be used as lambda

However this are valid
functional interfaces
interface Test3 {
public void doSomething();
public default void doSomethingDefault() {}
}
interface Test4 {
public void doSomething();
public static void doSomethingDefault() {}
}

Last note about
@FunctionalInterface(s)
This is valid
interface Test6<T> {
public T doSomething();
}
But this is invalid:
interface Test6 {
public <T> T doSomething();
}

2 notes about using Lambdas
on an API
• Lets assume we had the following method pre Java 8
public static void doIt(Integer a){}
• Let assume now.. That we want this integer to be fetched lazy or via some
method internally so we may add another method like this:
public static void doIt(Callable<Integer> a){ }
So far so good.

However pre Java 8 we had a chance
to do this for the next API version:
public static void doIt(Integer a){
}
public static void doIt(String a){
}
But now .. we cant add this:
public static void doIt (Callable<Integer> a){
}
public static void doIt (Callable<String> a){
}
Because the generics are removed and this two methods became the
same so we got duplicated method. So this is something we need to
think about when designing API.

Second note: Lets say we had only one
method with one generic type but we want
to use another interface
• So we had:
public static void doIt(Callable<Integer> a){
}
• and we may add
public static void doIt(Supplier<Integer> a){
}
• And that’s look fine… to us.

However when we try to call
this method(s)
doIt(() -> 5);
Now we (in fact all clients that used our API) get ambigous method.
And the only workaround for them is to change their code to something
like :
doIt((Callable<Integer>)() -> 5);
Which is… if first ugly and second it require manual change(s) in the
client code.

Stream API
 Databases and other programming languages
allow us to specify aggregate operations explicitly
 The stream API provides this mechanism in the
Java platform
 The notion of streams is derived from functional
programming languages

Stream API (2)
 The stream API makes use of lambdas and default
methods
 Streams can be applied on collections, arrays, IO
streams and generator functions
 Streams can be finite or infinite
 Streams can apply intermediate functions on the
data that produce another stream (e.g. map,
reduce)

Stream API usage
java.util.stream.Stream<T> collection.stream();
java.util.stream.Stream<T>
collection.parallelStream();

Stream API useful methods
 filter(Predicate), map(Function),
reduce(BinaryOperator), collect(Collector)
 min(Comparator), max(Comparator), count()
 forEach(Consumer)
 findAny(), findFirst()
 average(), sum()

Prior to Java 8, print even
numbers
List<Integer> ints = Arrays.asList(1, 2, 3, 4,
5, 6);
for (Integer anInt : ints) {
if (anInt % 2 == 0) {
System.out.println(anInt);
}
}

After java 8
List<Integer> ints = Arrays.asList(1, 2, 3, 4,
5, 6);
ints.stream()
.filter(i -> i % 2 == 0)
.foreach(i -> System.out.println(i));

Optional
The main point behind Optional is to wrap
an Object and to provide convenience API
to handle nullability in a fluent manner.
Optional<String> stringOrNot =
Optional.of("123");
//This String reference will never be null
String alwaysAString = stringOrNot.orElse("");

Optional in a nice example by
Venkat Subramanian
 Task : Double the first even number greater than 3
 Having as example the following input
List<Integer> values =
Arrays.asList(1,2,3,4,5,6,7,8,9,10);

Pre Java 8 way
int result = 0;
for(int e : values){
if(e > 3 && e% 2 == 0) {
result = e * 2;
break;
}
}
System.out.println(result);
Is it correct ? Is it ok ? .. Lets start eclipse and check

The new lambda way
System.out.println(
values.stream()
.filter(value -> value >3)
.filter(value -> value % 2 == 0)
.map(value -> value * 2)
.findFirst() );
Ones you write this 10 times its not that hard?

So in summary Optional is
heavily used in Stream API
// This Integer reference will be wrapped again
Optional<Integer> integerOrNot =
stringOrNot.map(Integer::parseInt);
// This int reference will never be null
int alwaysAnInt = stringOrNot
.map(s -> Integer.parseInt(s))
.orElse(0);

Method references
 Intended to be used in lambda expressions,
preventing unnecessary code
 Example:
books.stream().map(b -> b.getTitle()) ➔
books.stream().map(Book::getTitle)
 Lambda parameter list and return type must match
the signature of the method

Method references (2)
public class MainClass {
public static void main(String[] args) {
Function<Integer, Integer> f = MainClass::doSomething;
System.out.println(f.apply(5));
}
private static Integer doSomething(Integer amazingInteger) {
return amazingInteger;
}

Is iterative way better? Real
world example
Set<Seller> sellers = new HashSet<>();
for(Transaction t : txns) {
if(t.getBuyer().getAge() > 65) {
seller.add(t.getSeller());
}
}
List<Seller> sorted = new ArrayList<>(sellers);
Collections.sort(sorted, new Comperator<Seller>(){
public int compare(Seller a, Seller b){
return a.getName().compareTo(b.getName());
}
}
for(Seller s : sorted){
System.out.println(s.getName());
}

declarative way? Real world
example
txns.stream()
.filter(t -> t.getBuyer().getAge() > 65)
.map(t -> t.getSeller())
.distinct()
.sorted((s1,s2) ->
s1.getName().compareTo(s2.getName()))
.forEach(s -> System.out.println(s.getName));

Annotations in Java 5/6/7
• Annotations on class declarations
@Stateless
public class Person
• Annotations on method declarations
@Override
public String toString() {
• Annotations on class fields
@PersistenceContext
private EntityManager em;
• Annotations on method parameters
public Person getPersonByName(@PathParam("name")
String name) {

New in Java 8
You can put annotations anywhere a type is
specified:
public void sayHello() {
@Encrypted String data;
List<@NonNull String> strings;
HashMap names = (@Immutable
HashMap) map;
}

Gotchas
• Nobody will stop you doing bad things:
public void passPassword(
@Encrypted String pwd) {…}
public void hello() {
@PlainText String myPass = "foo";
passPassword(myPass);
}
• The code above will compile, run… and …crash

Also you cant override based
on Annotations
interface Test {
public void sayHello(@NotNull String notNull);
public void sayHelloNullable(String canNull);
}
class TestImpl implements Test {
@Override
public void sayHello(String notNull) {
// TODO Auto-generated method stub
}
@Override
public void sayHelloNullable(@NotNull String notNull) {
// TODO Auto-generated method stub
}
}

Method parameter names
• Before Java 8, only parameter positions and
types were preserved after compilation
• In Java 8 you can have those in the .class files
• They are not available by default
– Need to enable it with -parameters option to
javac
• And yes you can access this with Reflection…

Exact Numeric Operations
• Java 8 has added several new “exact” methods to the
Math class(and not only) protecting sensitive code
from implicit overflows
int safeC = Math.multiplyExact(bigA, bigB);
// will throw ArithmeticException if result exceeds +-2^31

Exact Numeric Operations(2)
4 new methods added to BigInteger class (also to
BigDecimal)
longValueExact(),
intValueExact(),
shortValueExact(),
and byteValueExact().
and toBigIntegerExact() for BigDecimal
All of the newly introduced “xxxxxExact()” methods throw
an ArithmeticException if the number contained in
the BigInteger instance cannot be provided in the
specified form without loss of information

Was ist das?
• Oracles runtime for ECMAScript 5.1
• GPL licensed
• Part of OpenJDK
• Just type jjs in the shell… and you are in!

Why ?
• Atwoods law: any application that can be written in
JavaScript, will eventually be written in JavaScript
• Oracle proving ground for support of dynamic languages
• Currently supports ECMAScript 5.1 (100%). No
backwards compatibility.
• Why not Rhino ? All code compiled to bytecode. No
interpretation.

Java -> JavaScript
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
public class EvalScript {
public static void main(String[] args) throws Exception {
// create a script engine manager
ScriptEngineManager factory = new ScriptEngineManager();
// create a Nashorn script engine
ScriptEngine engine = factory.getEngineByName("nashorn");
// evaluate JavaScript statement
try {
engine.eval("print('Hello, World!');");
} catch (final ScriptException se) { se.printStackTrace(); }
}
}

Multiple Invoke
import javax.script.Invocable;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
public class Eval_Invocable {
public static void main(String[] args) throws Exception {
ScriptEngineManager factory = new ScriptEngineManager();
ScriptEngine engine = factory.getEngineByName("nashorn");
engine.eval("function sum(x,y){return x+y}");
Invocable i = (Invocable) engine;
System.out.println(i.invokeFunction("sum",5,10));
System.out.println(i.invokeFunction("sum",10,15));
}
}

Implement Interface
public interface Adder {
int sum(int a,int b);
}
…
ScriptEngine engine = new
ScriptEngineManager().getEngineByName("nashorn");
engine.eval("var i = 5;n" +
"function run(){print(‘runnable’ + i++)}");
engine.eval("function sum(x,y){return x+y}");
Invocable i = (Invocable) engine;
Runnable r = i.getInterface(Runnable.class);
r.run();
Adder adder= i.getInterface(Adder.class);
System.out.println(adder.sum(1,3));

JavaScript -> Java
var timer = new java.util.Timer();
timer.schedule(
new java.util.TimerTask({
run: function(){
print("Tick")
}
})
,0,1000)
java.lang.Thread.sleep(5000)
timer.cancel();

Construct Java(Script)
objects
var linkedList = new java.util.LinkedList()
var LinkedList = java.util.LinkedList
var list = new LinkedList()
var LinkedList = Java.type(“java.util.LinkedList”)
var list = new LinkedList()

Types
var ints = new (Java.type(“int[]”))(6)
ints[0]=1
ints[1]=1.6
ints[2]=null
ints[3]=“45”
ints[4]=“str”
Ints[5]=undefined
print(ints)
print(java.util.Arrays.toString(ints))
Output will be:
[I@43re2sd
[1, 1, 0, 45, 0, 0]

Types(2)
var dbls = new (Java.type(“double[]”))(6)
dbls [0]=1
dbls [1]=1.6
dbls [2]=null
dbls [3]=“45”
dbls [4]=“str”
dbls [5]=undefined
print(dbls )
print(java.util.Arrays.toString(dbls ))
Output will be:
[D@43re2sd
[1.0, 1.6, 0.0, 45.0, NaN, NaN]

Type conversion
• Passing JavaScript values to Java methods will use
all allowed Java method invocation conversions…
+ all allowed JavaScript conversions
• All native JS objects implement java.util.Map
• And they do not implement java.util.List

Type conversion(2)
MyJavaClass.about(123);
// class java.lang.Integer
MyJavaClass.about(49.99);
// class java.lang.Double
MyJavaClass.about(true);
// class java.lang.Boolean
MyJavaClass.about("hi there")
// class java.lang.String
MyJavaClass.about(new Number(23));
// class jdk.nashorn.internal.objects.NativeNumber
MyJavaClass.about(new Date());
// class jdk.nashorn.internal.objects.NativeDate
MyJavaClass.about(new RegExp());
// class jdk.nashorn.internal.objects.NativeRegExp
MyJavaClass.about({foo: 'bar'});
// class jdk.nashorn.internal.scripts.JO4

Arrays conversion
• Not converted automatically!
• Explicit APIs provided:
var javaArray = Java.toJavaArray(jsArray,type)
var jsArray = Java.toJavaScriptArray(javaArray)

JavaScript lambdas
var stack = new java.util.LinkedList();
[1, 2, 3, 4,54,87,42,32,65,4,5,8,43].forEach(function(item) {
stack.push(item);
});
var sorted = stack
.stream()
.filter(function(i){return i%2==0})
.sorted()
.toArray();
print(java.util.Arrays.toString(sorted));
Output:
[2, 4, 4, 8, 32, 42, 54]

Scripting extensions
• Additional classpath elements can be specified
for the Java Virtual Machine (JVM).
• JavaScript strict mode can be activated.
• An intriguing scripting mode can be enabled.

Shell invocations
var lines =
`ls –lsa`.split("n");
for each (var line in lines) {
print("|> " + line);
}
Naydens-MacBook-Pro:SoftUniConf 2014 gochev$ jjs -scripting scripting.js
|> total 5328
|> 0 drwxrwxrwx 11 gochev staff 374 Sep 24 22:09 .
|> 0 drwxrwxrwx 12 gochev staff 408 Sep 22 18:03 ..
|> 16 -rw-r--r--@ 1 gochev staff 6148 Sep 24 00:15 .DS_Store
|> 0 drwxrwxrwx 7 gochev staff 238 Sep 22 16:59 0-BigIntegerDemo
|> 0 drwxrwxrwx 7 gochev staff 238 Sep 22 16:59 1-FirstEvenBlaBla

Shell invocations(2)
#!/usr/bin/env jjs -scripting
print("Arguments (${$ARG.length})");
for each (arg in $ARG) {
print("- ${arg}")
}
$ chmod +x executable.js
$ ./executable.js
Arguments (0)
$ ./executable.js -- hello world !
Arguments (3)
- hello
- world
- !

Do we still have time ? no
really ? RLY ?
OK so
“How Lambda magic work?”…
Are they like anonymous classes

What we(well… ok I) didn’t
speak about? …
• Date and Time Api
• Stamped Locks
• Concurrent Adders
• Parallel Streams showing why the streaming API is
so f*cking awesome
• JavaFX
• Secure Random generation
• AND A LOT MORE
(check this out www.baeldung.com/java8 )

Contacts
Blog : http://gochev.org
Facebook: https://www.facebook.com/gochev
Linkedin: https://www.linkedin.com/in/gochev
Skype: joke.gochev
Oh yes .. also http://dotnethater.blogspot.com

Software Uni Conf October 2014

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Software Uni Conf October 2014