DEV-1550: Why Java 8?
Or, What's a Lambda?
Julian Robichaux, panagenda

Who am I?
• Julian Robichaux
– Programmer and product manager at panagenda
– Developing applications using IBM products since mid-90’s
– Several open-source projects on OpenNTF
– “Learn Java by Example” video course
on lynda.com (LinkedIn Learning)
– IBM Champion since 2011
– nsftools.com (old stuff)
– @jrobichaux
2

Why are we here?
• To talk about Java 8!
– specifically lambdas and streams
– syntax, gotchas, and “why change?”
• Assuming that everyone in the room is a Java programmer
– you don’t have to be an expert
– any version is fine, we will start with Java 6
– we will also touch on Java 7, just in case
• What to do if you’re still on a Java 6 platform
3

Example Code
• Connect to a web server via HTTPS, and report the key size and expiration
date of the SSL certificate
– check servers for vulnerabilities due to old/weak keys
– tell your admins it’s time to renew the certificate
4
URL url = new URL( "https://my.server" );
checkSSLCertificate(url);

public static void checkSSLCertificate(URL url) {
HttpsURLConnection con = null;
try {
con = (HttpsURLConnection) url.openConnection();
con.setSSLSocketFactory( fakeSocketFactory() );
con.setHostnameVerifier(new HostnameVerifier() {
public boolean verify(String hostname, SSLSession session) {
return true; // trust everyone!
}
});
con.connect();
Certificate[] certs = con.getServerCertificates();
for (Certificate cert : certs) {
System.out.println( "Valid until: " + ((X509Certificate)cert).getNotAfter());
System.out.println( "Server key bit length: " +
((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() );
}
} catch (IOException e) {
e.printStackTrace();
} catch (GeneralSecurityException e) {
e.printStackTrace();
} finally {
con.disconnect();
}
}
Example Code (Java 6)
create an HTTPS connection
tell it that self-signed and
expired certificates are okay
report the expiration date and
RSA key length of each SSL
certificate on the server
Exception handling!

Example Code (Java 6)
/**
* Creates an SSLSocketFactory that doesn't check certificates at all
* DO NOT USE THIS IN REAL LIFE
*/
private static SSLSocketFactory fakeSocketFactory() throws GeneralSecurityException {
TrustManager trustEveryone = new X509TrustManager() {
public X509Certificate[] getAcceptedIssuers() { return null; }
public void checkServerTrusted(X509Certificate[] chain, String authType)
throws CertificateException {}
public void checkClientTrusted(X509Certificate[] chain, String authType)
throws CertificateException {}
};
SSLContext sslContext = SSLContext.getInstance("TLS");
sslContext.init(null, new TrustManager[] { trustEveryone }, new SecureRandom());
return sslContext.getSocketFactory();
}

A Few Words About Java 7
because you’ll see this stuff in Java 8

Catch Multiple Exceptions
• Try-catch blocks can catch multiple exceptions in one statement
HttpsURLConnection con = null;
try {
con = (HttpsURLConnection) url.openConnection();
// do stuff..
} catch (IOException e) {
e.printStackTrace();
} catch (GeneralSecurityException e) {
e.printStackTrace();
} finally {
con.disconnect();
}
HttpsURLConnection con = null;
try {
con = (HttpsURLConnection) url.openConnection();
// do stuff..
} catch (IOException | GeneralSecurityException e) {
e.printStackTrace();
} finally {
con.disconnect();
}

Try-with-resources
• Classes that implement the AutoCloseable interface can be automatically
closed by a try-catch block
HttpsURLConnection con = null;
try {
con = (HttpsURLConnection) url.openConnection();
// do stuff..
} catch (IOException | GeneralSecurityException e) {
e.printStackTrace();
} finally {
con.disconnect();
}
try (CloseableURLConnection closeableCon = new CloseableURLConnection(url)) {
HttpsURLConnection con = closeableCon.getHttpsConnection();
// do stuff..
} catch (IOException | GeneralSecurityException e) {
e.printStackTrace();
}
*
*
*

Creating a Closeable Class
static class CloseableURLConnection implements AutoCloseable {
URLConnection con;
public CloseableURLConnection(URL url) throws IOException {
con = url.openConnection();
}
public HttpsURLConnection getHttpsConnection() {
return (HttpsURLConnection)con;
}
@Override
public void close() {
getHttpsConnection().disconnect();
}
}
implement AutoCloseable
create a close() method

Closeable Classes
• Several standard Java classes are now AutoClosable
– InputStream
– OutputStream
– Reader
– Writer
– java.sql.Connection, Statement, and ResultSet
• You no longer have to declare your streams outside the try/catch block, or
remember to close them when you’re done!
• Like a finally clause, try-with-resources objects get closed even if an
Exception is thrown
11

A Few Other Java 7 Goodies
• New and/or improved classes
– java.nio.file, updated XML libraries, new/enhanced cryptography providers
• Binary literals and underscores in numeric literals
– int byteNum = 0b00100001;
– int phoneNum = 555_1212;
• Type inference for generics
– Map<String, List<String>> map = new HashMap<>();
• Switch statements operate on Strings
• http://docs.oracle.com/javase/8/docs/technotes/guides/language/enhancements.html
http://www.oracle.com/technetwork/java/javase/jdk7-relnotes-418459.html

And Now: Java 8
on to the good stuff

The Code in Java 7…
public static void checkSSLCertificate(URL url) {
try (CloseableURLConnection closeableCon = new CloseableURLConnection(url)) {
HttpsURLConnection con = closeableCon.getHttpsConnection();
con.setSSLSocketFactory( fakeSocketFactory() );
con.setHostnameVerifier(new HostnameVerifier() {
public boolean verify(String hostname, SSLSession session) {
return true; // trust everyone!
}
});
con.connect();
Certificate[] certs = con.getServerCertificates();
for (Certificate cert : certs) {
System.out.println( "Valid until: " + ((X509Certificate)cert).getNotAfter());
System.out.println( "Server key bit length: " +
((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() );
}
} catch (IOException | GeneralSecurityException e) {
e.printStackTrace();
}
}
anonymous class
loop through an array

The Code in Java 8
public static void checkSSLCertificate(URL url) {
try (CloseableURLConnection closeableCon = new CloseableURLConnection(url)) {
HttpsURLConnection con = closeableCon.getHttpsConnection();
con.setSSLSocketFactory( fakeSocketFactory() );
con.setHostnameVerifier( (hostname, session) -> true );
con.connect();
Certificate[] certs = con.getServerCertificates();
Arrays.asList(certs)
.stream()
.map ( cert -> (X509Certificate)cert )
.peek( cert -> System.out.println("Valid until: " + cert.getNotAfter()) )
.map ( cert -> ((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() )
.forEach( i -> System.out.println("Server key bit length: " + i) );
} catch (IOException | GeneralSecurityException e) {
e.printStackTrace();
}
}
lambda hostname verifier
read the array as a stream,
not a loop

What’s a Lambda?
• Simplified syntax for writing single-method classes
• You are effectively passing a function as a parameter to a method
16
con.setHostnameVerifier( (hostname, session) -> true );
(parameters)
arrow
expression

How Does that Lambda Work?
con.setHostnameVerifier( new HostnameVerifier() {
public boolean verify(String hostname, SSLSession session) {
return true;
}
});
con.setHostnameVerifier( (hostname, session) -> true );
?

How Does that Lambda Work?
con.setHostnameVerifier( new HostnameVerifier() {
public boolean verify(String hostname, SSLSession session) {
return true;
}
});
con.setHostnameVerifier( (hostname, session) -> true );
?

How Does that Lambda Work?
con.setHostnameVerifier( new HostnameVerifier() {
public boolean verify(String hostname, SSLSession session) {
return true;
}
});
con.setHostnameVerifier( (hostname, session) -> true );
?

How Does that Lambda Work?
con.setHostnameVerifier( new HostnameVerifier() {
public boolean verify(String hostname, SSLSession session) {
return true;
}
});
con.setHostnameVerifier( (hostname, session) -> true );
?

How Does that Lambda Work?
con.setHostnameVerifier( new HostnameVerifier() {
public boolean verify(String hostname, SSLSession session) {
return true;
}
});
con.setHostnameVerifier( (hostname, session) -> true );
!

Functional Interfaces
• Lambdas rely on “functional interfaces” to work
– an interface with only one abstract method
– also called a “single abstract method” or SAM interface
– there can be only one! <insert highlander joke here>
• If there’s only one method, the compiler knows which one you will call
• If you know the method, and the compiler knows the method, we don’t
have to talk about the method
– everyone already knows!
– skip the obvious stuff
22

Functional Interfaces
con.setHostnameVerifier( new HostnameVerifier() {
public boolean verify(String hostname, SSLSession session) {
return true;
}
});
con.setHostnameVerifier( (hostname, session) -> true );
the class MUST be a HostnameVerifier, and the
method MUST be verify(String, SSLSession)
therefore… throw away everything obvious

Lambda Syntax
object.method( (param1, param2) -> result );
object.method( param1 -> doStuff(param1) );
object.method( param1 -> doStuff(param1, object) );
object.method( () -> {
doStuff();
return doMoreStuff();
} );

Method References
• There is an alternative syntax called “Method References”
– for a lambda that only calls a single method of the parameter, or a single
static method that uses the parameter, or creates a single new Object
object.method( s -> s.getLength() );
object.method( String::getLength );
http://docs.oracle.com/javase/tutorial/java/javaOO/methodreferences.html

Another Example: Sandwiches!
static enum Sandwich {
PB_J ("Peanut butter & jelly", 500),
SUB ("Sub", 500),
HOTDOG ("Hot dog", 900),
TACO ("Taco", 500),
PIZZA ("Pizza", 900);
private String name;
private int calories;
private Sandwich(String name, int calories) {
this.name = name;
this.calories = calories;
}
public String getName() { return name; }
public int getCalories() { return calories; }
public String toString() { return "n" + calories +
" caloriest" + name; }
}

List the Sandwiches in Order of Calories
List<Sandwich> sandwiches = Arrays.asList( Sandwich.values() );
Collections.sort(sandwiches, new Comparator<Sandwich>() {
public int compare(Sandwich s1, Sandwich s2) {
return Integer.compare(s1.getCalories(), s2.getCalories());
}
});
System.out.println(sandwiches);
PB_J ("Peanut butter & jelly", 500),
SUB ("Sub", 500),
HOTDOG ("Hot dog", 900),
TACO ("Taco", 500),
PIZZA ("Pizza", 900);
500 calories Peanut butter & jelly,
500 calories Sub,
500 calories Taco,
900 calories Hot dog,
900 calories Pizza

List the Sandwiches in Order of Calories
List<Sandwich> sandwiches = Arrays.asList( Sandwich.values() );
/*
Collections.sort(sandwiches, new Comparator<Sandwich>() {
public int compare(Sandwich s1, Sandwich s2) {
return Integer.compare(s1.getCalories(), s2.getCalories());
}
});
*/
Collections.sort(sandwiches,
(s1, s2) -> Integer.compare(s1.getCalories(), s2.getCalories()) );
System.out.println(sandwiches);
PB_J ("Peanut butter & jelly", 500),
SUB ("Sub", 500),
HOTDOG ("Hot dog", 900),
TACO ("Taco", 500),
PIZZA ("Pizza", 900);
500 calories Peanut butter & jelly,
500 calories Sub,
500 calories Taco,
900 calories Hot dog,
900 calories Pizza

List the Sandwiches in Order of Calories
List<Sandwich> sandwiches = Arrays.asList( Sandwich.values() );
/*
Collections.sort(sandwiches, new Comparator<Sandwich>() {
public int compare(Sandwich s1, Sandwich s2) {
return Integer.compare(s1.getCalories(), s2.getCalories());
}
});
*/
Collections.sort(sandwiches,
Comparator.comparing( sandwich -> sandwich.getCalories() ) );
System.out.println(sandwiches);
PB_J ("Peanut butter & jelly", 500),
SUB ("Sub", 500),
HOTDOG ("Hot dog", 900),
TACO ("Taco", 500),
PIZZA ("Pizza", 900);
500 calories Peanut butter & jelly,
500 calories Sub,
500 calories Taco,
900 calories Hot dog,
900 calories Pizza

List the Sandwiches in Order of Calories
List<Sandwich> sandwiches = Arrays.asList( Sandwich.values() );
/*
Collections.sort(sandwiches, new Comparator<Sandwich>() {
public int compare(Sandwich s1, Sandwich s2) {
return Integer.compare(s1.getCalories(), s2.getCalories());
}
});
*/
Collections.sort(sandwiches,
Comparator.comparing( Sandwich::getCalories ) );
System.out.println(sandwiches);
PB_J ("Peanut butter & jelly", 500),
SUB ("Sub", 500),
HOTDOG ("Hot dog", 900),
TACO ("Taco", 500),
PIZZA ("Pizza", 900);
500 calories Peanut butter & jelly,
500 calories Sub,
500 calories Taco,
900 calories Hot dog,
900 calories Pizza

All These are the Same Comparator
Collections.sort(sandwiches, new Comparator<Sandwich>() {
public int compare(Sandwich s1, Sandwich s2) {
return Integer.compare(s1.getCalories(), s2.getCalories());
}
});
Collections.sort(sandwiches,
(s1, s2) -> Integer.compare(s1.getCalories(), s2.getCalories()) );
Collections.sort(sandwiches,
Comparator.comparing( sandwich -> sandwich.getCalories() ) );
Collections.sort(sandwiches,
Comparator.comparing( Sandwich::getCalories ) );

Fun with the Comparator
Collections.sort(sandwiches,
Comparator.comparing( Sandwich::getCalories )
.thenComparing( Sandwich::getName )
.reversed() );
900 calories Pizza,
900 calories Hot dog,
500 calories Taco,
500 calories Sub,
500 calories Peanut butter & jelly
PB_J ("Peanut butter & jelly", 500),
SUB ("Sub", 500),
HOTDOG ("Hot dog", 900),
TACO ("Taco", 500),
PIZZA ("Pizza", 900);

But Really, What’s the Point?
• This all seems like needless tomfoolery
– after all, the old code still works!
• Two major advantages:
1. Forces (or strongly encourages) you to write functional code
2. Less visual noise makes code easier to read and understand
33
Collections.sort(sandwiches, new Comparator<Sandwich>() {
public int compare(Sandwich s1, Sandwich s2) {
return Integer.compare(s1.getCalories(), s2.getCalories());
}
});
Collections.sort(sandwiches,
Comparator.comparing( Sandwich::getCalories ) );

Code Should Describe Behavior
Code Should Read Like A Story

Dealing with Exceptions
Collections.sort(sandwiches,
Comparator.comparing( Sandwich::getCalories )
.thenComparing( Sandwich::getName )
.reversed() );
NULLWICH (null, 500),
PB_J ("Peanut butter & jelly", 500),
SUB ("Sub", 500),
HOTDOG ("Hot dog", 900),
TACO ("Taco", 500),
PIZZA ("Pizza", 900);
Exception in thread "main" java.lang.NullPointerException
at java.util.Comparator.lambda$comparing$77a9974f$1(Comparator.java:469)
at java.util.Comparator.lambda$thenComparing$36697e65$1(Comparator.java:217)
at java.util.Collections$ReverseComparator2.compare(Collections.java:5178)
at java.util.TimSort.countRunAndMakeAscending(TimSort.java:355)
at java.util.TimSort.sort(TimSort.java:220)
at java.util.Arrays.sort(Arrays.java:1438)
at java.util.Arrays$ArrayList.sort(Arrays.java:3895)
at java.util.Collections.sort(Collections.java:175)
at com.panagenda.ssltest.MoreJava8Examples.main(MoreJava8Examples.java:52)

Dealing with Exceptions
• It’s not always obvious what caused the Exception
• It’s cumbersome to add a try/catch to a lambda
– same with adding logging
• If an Exception is possible, maybe better to call out to a method instead
36
Collections.sort(sandwiches,
Comparator.comparing( sandwich -> getCalories(sandwich) )
.thenComparing( sandwich -> getName(sandwich) )
.reversed() );

A Few More Examples
// process all the keys and values of a HashMap
Map<String, Integer> myHashMap = new HashMap<>();
myHashMap.forEach( (key, value) -> System.out.println(key + "; " + value) );
// remove all the null elements in a List
List<String> myArrayList = new ArrayList<>();
myArrayList.removeIf( s -> s == null );
// get all the JPG files in a directory
File photoDir = new File("c:/photos");
File[] docFiles = photoDir.listFiles( file -> file.getName().endsWith("jpg") );
// run some code in a thread
new Thread( () -> doSomething() ).start();

Under the Hood
• If you’re really curious about how all this works…
– http://cr.openjdk.java.net/~briangoetz/lambda/lambda-translation.html
• It’s all Function and Predicate objects
– https://docs.oracle.com/javase/8/docs/api/java/util/function/package-
summary.html
– Closures? By some definitions.
38
Function<Sandwich, Integer> caloryCompare = sandwich -> sandwich.getCalories();

Streams!
of data, not water

From Loop to Stream
Certificate[] certs = con.getServerCertificates();
for (Certificate cert : certs) {
System.out.println( "Valid until: " + ((X509Certificate)cert).getNotAfter());
System.out.println( "Server key bit length: " +
((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() );
}
Certificate[] certs = con.getServerCertificates();
Arrays.asList(certs)
.stream()
.map ( cert -> (X509Certificate)cert )
.peek( cert -> System.out.println("Valid until: " + cert.getNotAfter()) )
.map ( cert -> ((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() )
.forEach( i -> System.out.println("Server key bit length: " + i) );
?

What Does that Loop Actually Do?
41
Certificate[] certs = con.getServerCertificates();
for (Certificate cert : certs) {
System.out.println( "Valid until: " + ((X509Certificate)cert).getNotAfter());
System.out.println( "Server key bit length: " +
((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() );
}
print the information
get something from the objectprint the information
get something from the object

How Does the Stream Work?
Certificate[] certs = con.getServerCertificates();
Arrays.asList(certs)
.stream()
.map ( cert -> (X509Certificate)cert )
.peek( cert -> System.out.println("Valid until: " + cert.getNotAfter()) )
.map ( cert -> ((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() )
.forEach( i -> System.out.println("Server key bit length: " + i) );
start with an array,
convert it to a List
convert the List to a stream
TIP: this could also be just
Arrays.stream(certs)
}
change the stream
do something to each item
change the stream
do something to each item

Breaking Down the Example
Certificate[] certs = con.getServerCertificates();
Arrays.asList(certs)
.stream()
.map ( cert -> (X509Certificate)cert )
.peek( cert -> System.out.println("Valid until: " + cert.getNotAfter()) )
.map ( cert -> ((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() )
.forEach( i -> System.out.println("Server key bit length: " + i) );
map() converts each item by
casting it to X509Certificate,
then returns a Stream of
X509Certificate objects
map() gets an int value from
each item, then returns a
Stream of int values
start with an array of
Certificates

Breaking Down the Example
Certificate[] certs = con.getServerCertificates();
Arrays.asList(certs)
.stream()
.map ( cert -> (X509Certificate)cert )
.peek( cert -> System.out.println("Valid until: " + cert.getNotAfter()) )
.map ( cert -> ((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() )
.forEach( i -> System.out.println("Server key bit length: " + i) );
peek() is an intermediate
operation: it does something
with each item and returns
the original Stream
forEach() is a terminal
operation: it does something
with each item and stops

What’s a Stream?
• Allows you to perform operations on a collection of data
– multiple operations can be combined in a pipeline
• Has the following properties
– uses functional arguments (lambdas!) to process data
– does not store data
– pipeline operations are optimized for laziness
– optionally process in parallel (multi-threaded) with no extra code
45

Is a Stream Better than a Loop?
Certificate[] certs = con.getServerCertificates();
for (Certificate cert : certs) {
System.out.println( "Valid until: " + ((X509Certificate)cert).getNotAfter());
System.out.println( "Server key bit length: " +
((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() );
}
Certificate[] certs = con.getServerCertificates();
Arrays.asList(certs)
.stream()
.map ( cert -> (X509Certificate)cert )
.peek( cert -> System.out.println("Valid until: " + cert.getNotAfter()) )
.map ( cert -> ((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() )
.forEach( i -> System.out.println("Server key bit length: " + i) );
!Stream version is more
descriptive of the behavior
of the code
Stream version can easily be
turned into multi-threaded
code

Multi-threaded You Say?
Arrays.asList(certs)
.stream()
.parallel()
.map ( cert -> (X509Certificate)cert )
.peek( cert -> System.out.println("Valid until: " + cert.getNotAfter()) )
.map ( cert -> ((RSAPublicKey)cert.getPublicKey()).getModulus().bitLength() )
.forEach( i -> System.out.println("Server key bit length: " + i) );
DANGER: The forEach() and peek()
output might be out-of-order!

Adding Numbers in a Loop
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9
45
int sum = 0;
for (int i : new int[] {1, 2, 3, 4, 5, 6, 7, 8, 9}) {
sum += i;
}
return sum;

Adding Numbers with Reduce
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9
1 + 2 3 + 4 + 5 6 + 8 7 + 9
3 + 14 12 + 16
45

Adding Numbers with Reduce
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9
1 + 2 3 + 4 + 5 6 + 8 7 + 9
3 + 14 12 + 16
45
By abstracting away the very concept
of looping, you can implement looping
any way you want, including
implementing it in a way that scales
nicely with extra hardware.
Joel Spolsky
https://www.joelonsoftware.com/2006/08/01/
can-your-programming-language-do-this
each computation could be on a separate processor core… or a separate machine!

Other Things to Know About Streams
• Normally get them from Collections or arrays
– List.stream(), Map.entrySet().stream(), Arrays.stream(Object[])
– also other fun places, like BufferedReader.lines() or Files.list()
• Some operations will short circuit instead of processing each item
– built-in optimizations
• Stream operations should be stateless
– for example, don’t update Lists as part of a stream operation
– items could process out of order, and might not be thread-safe
– collect the results at the end instead
51

Other Things to Know About Streams
• Operations on Streams should be associative when possible
– (a + b + c) == (c + b + a) == b + (a + c)
– if order of operations does matter, make sure you:
• start with an ordered set of data, like a List
• use forEachOrdered() instead of forEach()
• don’t use reduce()
• For reference:
– https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-
summary.html
52

Under the Hood
• If you’re really curious about how all this works…
– http://www.ibm.com/developerworks/java/library/j-java-streams-1-brian-
goetz
• Read about java.util.function
– https://docs.oracle.com/javase/8/docs/api/java/util/function/package-
summary.html
– Predicate, Consumer, and Supplier interfaces
53

Backwards Compatibility
because not all of us have a choice

Java 8 API Changes (partial list)
• Streams
– in its own package
– throughout Collections, Files, etc.
• Functional classes in java.util.function
• Brand new Date-Time package and classes
– http://docs.oracle.com/javase/tutorial/datetime
• JavaFX for GUIs
• http://www.oracle.com/technetwork/java/javase/8-whats-new-2157071.html
http://docs.oracle.com/javase/8/docs/technotes/guides/language/lambda_api_jdk8.html
55
Function<Sandwich, Integer> caloryCompare =
sandwich -> sandwich.getCalories();

Compiling to Earlier Versions
• Java can compile for previous versions, but…
– you can’t use any of the new APIs (classes or methods)
– you can’t use any of the new language features
• What happens if you use a Java 8 JAR in a Java 6 environment?
– it won’t work
– the JRE checks the JAR file for a version number first
– if the version number is too high, you get errors
• Some tools can convert bytecode to earlier versions
– but new APIs still won’t work
56

Options for Backwards Compatibility
• If you don’t want to use new language features at all
– set “Source compatibility” and “Generated .class files compatibility” to your
desired older Java version
– use a tool to make sure you didn’t use new APIs
Animal Sniffer: http://www.mojohaus.org/animal-sniffer
57

Options for Backwards Compatibility
• If you only want to use lambdas and try-with-resources
– compile as Java 8, then use RetroLambda to backport your JAR file
https://github.com/orfjackal/retrolambda
– you still have to make sure you didn’t use new APIs: AnimalSniffer again
• You might be able to backport Streams too (mixed results)
– http://sourceforge.net/projects/streamsupport
58

Is It Worth It?
• Backporting? Maybe, but probably not regularly
– Risky: even if it seems to work, hard to test if it really worked
– make sure you have great unit tests to run against the backported code
• Learning? Absolutely!
– even if you can’t use Java 8 now, you will later
– functional programming can be much “safer”
– teaches you good coding habits
– helps you understand code examples on StackOverflow ;)
59

Required Reading
we only scratched the surface

On the Oracle Website
• Streams
– https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-
summary.html
– http://www.oracle.com/technetwork/articles/java/ma14-java-se-8-
streams-2177646.html
• Lambdas
– https://docs.oracle.com/javase/tutorial/java/javaOO/
lambdaexpressions.html
– http://docs.oracle.com/javase/tutorial/java/javaOO/methodreferences.html
– https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.27
61

Articles and Musings
• State of the lambda (Brian Goetz)
– http://cr.openjdk.java.net/~briangoetz/lambda/lambda-state-final.html
• IBM DeveloperWorks articles by Brian Goetz
– http://www.ibm.com/developerworks/java/library/j-java-streams-1-brian-goetz
– http://www.ibm.com/developerworks/java/library/j-java-streams-2-brian-goetz
– http://www.ibm.com/developerworks/java/library/j-java-streams-3-brian-goetz
– http://www.ibm.com/developerworks/java/library/j-java-streams-4-brian-goetz
– http://www.ibm.com/developerworks/java/library/j-java-streams-5-brian-goetz
• Joel Spolsky on MapReduce
– https://www.joelonsoftware.com/2006/08/01/can-your-programming-language-
do-this
62

Books (!)
• Java 8 in Action
– Raoul-Gabriel Urma
Manning Press
• Mastering Lambdas:
Java Programming in
a Multicore World
– Maurice Naftalin
Oracle Press

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65

Thank you!
Julian Robichaux
@jrobichaux
jrobichaux@panagenda.com