Post on 04-Jun-2020
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JDK 7 and BeyondModularity and ClosureLee Chuk Munnchuk-munn.lee@oracle.com
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Agenda
• Project Coin• Modularity• Closures
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Section DividerSmallSmall
(Language)(Language)ChangesChanges
Project CoinProject Coin
Better Integer Literal• Binary literals
• With underscores for clarity
int mask = 0b101010101010;
int mask = 0b1010_1010_1010;long big = 9_223_783_036_967_937L;
String Switch Statement• Today case label includes integer constants and enum
constants• Strings are constants too
Discriminating Strings Today
int monthNameToDays(String s, int year) {
if("April".equals(s) || "June".equals(s) ||"September".equals(s) ||"November".equals(s))
return 30;
if("January".equals(s) || "March".equals(s) ||"May".equals(s) || "July".equals(s) ||"August".equals(s) || "December".equals(s))
return 31;
if("February".equals(s))...
With String Switchint monthNameToDays(String s, int year) {
switch(s) {case "April": case "June":case "September": case "November":
return 30;
case "January": case "March":case "May": case "July":case "August": case "December":
return 31;
case "February":...
default:...
Inferring Types with <>• Pre generics
• With generics
• With diamond (<>) to infer the type
List strList = new ArrayList();
List<String> strList = new ArrayList<String>();
List<Map<String, List<String>> strList =new ArrayList<Map<String, List<String>>();
List<String> strList = new ArrayList<>();
List<Map<String, List<String>> strList =new ArrayList<>();
Exceptions Galoretry {
...} catch(ClassNotFoundException cnfe) {
log(cnfe);throw cnfe;
} catch(InstantiationException ie) {log(ie);throw ie;
} catch(NoSuchMethodException nsme) {log(nsme);throw nsme;
} catch(InvocationTargetException ite) {log(ite);throw ite;
}
Multi-Catch
try {// Reflective operations calling Class.forName,// Class.newInstance, Class.getMethod,// Method.invoke, etc.
} catch(final ClassNotFoundException |InstantiationException |NoSuchMethodException |InvocationTargetException e) {
log(e);throw e;
}
Copying Streams
InputStream in = new FileInputStream(src);OutputStream out = new FileOutputStream(dest);
byte[] buf = new byte[8192];int n;
while ((n = in.read(buf)) >= 0)out.write(buf, 0, n);
• How to make this piece of code robust?
InputStream in = null;OutputStream out = null;try {
in = new FileInputStream(src);} catch (FileNotFoundException fne) {
return;}try {
out = new FileOutputStream(dst);try {
byte[] buf = new byte[8192];int n;while ((n = in.read(buf)) >= 0)
out.write(buf, 0, n);} catch (IOException ioe) {
//Do something} finally {
try {out.flush();out.close();
} catch (IOException ioe) { }}
} catch (FileNoutFoundException fne) {} finally {
try {in.close();
} catch (IOException ioe) { }}
Automatic Resource Management
• API support– New interface java.lang.AutoClosable– java.io.Closable– JDBC 4.1 retrofitted to use AutoClosable
try (InputStream in = new FileInputStream(src);OutputStream out = new FileOutputStream(ds)) {byte[] buf = new byte[8192];int n;
while ((n = in.read(buf)) >= 0)out.write(buf, 0, n);
}
ModularityModularityProject JigsawProject Jigsaw
Modularity – the Solution• “JAR hell”
– Eliminates class path– Package modules for automatic download & install– Generate native packages – deb, rpm, ips, etc
• Performance – download time, startup time– Incremental download → fast classloading– Remembering startup classes
• Platform scalability – down to small devices– SE subset can fit into small devices
Modularity Goals• Grouping• Dependencies• Versioning• Encapsulation• Optional modules• Virtual modules
Packages
package com.foo.app
public class Main {
public class Other {
package com.foo.app.ui
public class Shell {
com.foo.app.Main
com.foo.app.Other
com.foo.app.ui.Shell
com.foo.app
module-info.java
module com.foo.app @ 1.0.0 {class com.foo.app.Mainprovides com.foo.app.lib @ 1.0.0;
}
Entry point
Module name Version
Virtual module
com.foo.app.Main
com.foo.app.Other
com.foo.app.ui.Shell
com.foo.app
module-info.java
com.foo.app
org.bar.lib
com.foo.lib
edu.baz.util
module com.foo.app @ 1.0.0 {class com.foo.app.Mainrequires com.foo.lib @ 2.1-alpha;provides com.foo.app.lib @ 1.0.0;
}
Dependency
import com.foo.lib.*;public class Main {
module-info.java
com.foo.app
org.bar.lib
com.foo.lib
edu.baz.util
com.foo.extra
Optional modules
module com.foo @ 1.0.0 {class com.foo.app.Mainrequires com.foo.lib @ 2.1-alpha;provides com.foo.app.lib @ 1.0.0;requires optional com.foo.extra;
}
module-info.java
com.foo.app
com.foo.secret
org.bar.lib
com.foo.lib
edu.baz.util
com.foo.extramodule com.foo.secret @ 1 {permits com.foo.lib;
}
Encapsulating modules
Packaging
$ javac -modulepath mods src/com.foo.app/...
$ ls mods com.foo.app/com.foo.extra/com.foo.lib/
Packaging
$ javac -modulepath mods src/com.foo.app/...
$ ls mods com.foo.app/com.foo.extra/com.foo.lib/
$ ls -R mods/com.foo.appmods/com.foo.app/com/foo/app/Main.classmods/com.foo.app/com/foo/app/Other.classmods/com.foo.app/com/foo/ui/Shell.class
Packaging
$ javac -modulepath mods src/com.foo.app/...
$ ls mods com.foo.app/com.foo.extra/com.foo.lib/
$ jpkg -modulepath mods jmod \com.foo.app com.foo.extra com.foo.lib
$ ls *.jmodcom.foo.app@1.0.0.jmodcom.foo.extra@0.9a.jmodcom.foo.lib@1.0.2.jmod
Library
$ ls *.jmodcom.foo.app@1.0.0.jmodcom.foo.extra@0.9a.jmodcom.foo.lib@1.0.2.jmod
$ jmod -L mlib create
./mlib
Library
org.bar.lib
edu.baz.util
./mlib$ ls *.jmodcom.foo.app@1.0.0.jmodcom.foo.extra@0.9a.jmodcom.foo.lib@1.0.2.jmod
$ jmod -L mlib install \ $EXT/edu.baz.util@*.jmod \ $EXT/org.bar.lib@*.jmod
Library
$ ls *.jmodcom.foo.app@1.0.0.jmodcom.foo.extra@0.9a.jmodcom.foo.lib@1.0.2.jmod
$ jmod -L mlib install \ *.jmod
$ jmod -L mlib lscom.foo.app @ 1.0.0com.foo.extra @ 0.9acom.foo.lib @ 1.0.2edu.baz.util @ 5.2_11org.bar.lib @ 2.1-alpha
com.foo.app
org.bar.lib
com.foo.lib
edu.baz.util
com.foo.extra
./mlib
Execution
$ java -L mlib \ -m com.foo.app
Welcome to Foo...
com.foo.app
org.bar.lib
com.foo.lib
edu.baz.util
com.foo.extra
./mlib
Library Delegation
ORACLE CONFIDENTIAL
com.foo.app
org.bar.lib
com.foo.lib
edu.baz.util
com.foo.extra
jdk.base
jdk.boot
jdk.desktop
jdk.xml
$JRE/lib/modules
./mlib
Repositories
ORACLE CONFIDENTIAL
jdk.base
jdk.boot
jdk.desktop
jdk.xml
$JRE/lib/modules
http://jig.sfbay/linux/x86
jdk.tools@7-ea.jmod
jdk.corba@7-ea.jmod
jdk.jndi@7-ea.jmod
...
$ jmod add-repo http://jig.sfbay
$ jmod install jdk.toolsDownloading jdk.tools@7-ea ...Configuring jdk.tools@7-ea ...
Native Packages
com.foo.app@1.0
com.foo.lib@3.22
$ jpkg -m mods deb com.foo.app com.foo.lib
com.foo.app-1.0.deb
com.foo.lib-3.22.deb
Requires: com.foo.lib >= 3.0
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Section Divider
ClosureClosureProject LambdaProject Lambda
Motivation for Lambda Project• Moore's law, multi core chip• Library is one of Java's key strength
– Better libraries are key to making parallelization better
• Higher level operations tend to improve readability of code as well as performance
• Without more language support for parallel idioms, people will instinctively reach for serial idioms
For loop – External Iteration
• Code is inherently serial– Stateful – use of > and highestScore– Client (for loop) of students determines iteration mechanism
• Serial – from first to last – no requirement for ordering
Collection<Student> students = ...
double highestScore = 0.0;for (Student s : students) {
if ((s.gradYear == 2010) && (s.score > highestScore))
highestScore = s.score;}
Hypothetical Collection Methods
• Assume collection has filter, map, reduce, max, etc.
• Not inherently serial– students traversal not determined by developer
• Anonymous inner class!– Too much boiler plate code
double highestScore = students.filter(new Predicate<Student>() {
public boolean isTrue(Student s) {return s.gradYear == 2010;
}}).map(new Extractor<Student,Double>() {
public Double extract(Student s) {return s.score;
}}).max();
Introducing Lambda Expressions
• Lambda expressions introduced with #– Signal to the JVM to defer execution of the code
• Zero or more formal parameters– Like methods
• Body may be an expression or statement– If expression, no need 'return' or ';'– Unlike methods
double highestScore = students.filter(#{ Student s -> s.gradYear == 2010 }).map(#{ Student s -> s.score }).max();
Lambda Expression
#{ Student s -> s.gradYear == 2010 }
Denotes lambda expression
Body
Formal parameter(s)
Lambda Expressions – Internal Iteration
• Cleaner syntax• Potentially faster because collection (implementation)
determines how to iterate– Opportunities for lazy evaluation– Opportunities for parallelism
double highestScore = students.filter(#{ Student s -> s.gradYear == 2010 }).map(#{ Student s -> s.score }).max();
Lambda Expression Type
• A function type from Student to boolean• Java does not have function types
– But have single method interfaces (or abstract classes)
– “Function type” from T to int
#{ Student s → s.gradYear == 2010 }
public interface Comparable<T> {public int compareTo(T object);
}
SAM Types• SAM type is an interface or abstract class with a
Single Abstract Method– Examples of existing SAM type in JDK
• No special syntax to declare SAM type
interface Runnable { void run(); }interface Callable<T> { T call(); }interface ActionListener {
void actionPerformed(ActionEvent evt); }interface Comparable<T> {
int compareTo(T obj); }
SAM Conversion• Infers a SAM type from a lambda expression
– Same parameter types and arity as SAM type's method– Return type compatible with SAM type's method– Checked exceptions compatible with SAM type's method
• SAM type's method name is not relevant– Almost like duck typing
ActionListener listener = #{ ActionEvent aEvt ->System.out.println(“hello world”); });
//void run();Runnable run = #{ ->
System.out.println(“hello world”); });//void dispatch();ActiveEvent event = #{ ->
System.out.println(“hello world”); });
Benefits of SAM Type• Target typing – inferring types from SAM type's
method– Can omit formal parameter type
• Compatibility with existing libraries
• No special method to invoke lambda expression– Just call the SAM type's method
button.addActionListener(#{ aEvt ->System.out.println(“hello”); });
ActionListener listener = #{ ... };listener.actionPerformed(new ActionEvent( ... ));
button.addActionListener(#{ aEvt ->System.out.println(“hello”); });
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