Java 7 - What's New?

What’s New in Java 7?

copyright 2011 Trainologic LTD

What’s new in Java 7?

New Features in Java 7

• Dynamic Languages Support.
• Project Coin.
• Fork/Join Library.
• NIO2.

• Most important features (e.g., lambda functions,
modularization) are deferred to Java 8.

4


New Bytecode Instruction

• Java 7 introduces a change in the JVM bytecode
instructions.
• This has not been done in many releases.
• The new bytecode instruction available in Java 7 is:
invokedynamic.

4


Dynamic Languages Support

• Java 6 introduced the Scripting API for scripting support
for dynamic languages.
• Although you can create now applications that will run
scripts in many languages (e.g., Jython, Groovy,
JavaScript) compilation of dynamic languages is a
problem.
• Now, why is that?

4


Dynamic Languages Support

• The current bytecode instructions only provide method
invocations that are strongly types (i.e., types of
arguments must be know in advance).
• That makes a burden on compilers for dynamic
languages and often results in performance degradation
and poor generated code.
• The new mechanism allows for dynamically generated
methods to be added and invoked.

4


Project Coin

• Project Coin introduces changes to the syntax of the
Java language.
• Note that these are not major changes as were done in
Java 5.

• Let’s see what it is about…

4


Project Coin

• Project Coin includes:
• Support for strings in switch statements.
• Binary numeric literals.
• Improved type inference.
• Multi-catch.
• Precise rethrow.
• ARM (Automatic Resource Management).

4


Switch on Strings

• The current JVM does not allow switch on non integer
types.
• I.e., only int, short, byte, char and Enum are allowed.
• The new version will also support Strings.

• Now, this was done without altering the bytecode.
• I.e., by using compilation techniques.

• Let’s see an example…

4


Example

• Switch on strings:
switch (str) {
case "a":
System.out.println("is a");
break;
case "bcd":
System.out.println("string is bcd");
break;
default:
System.out.println("couldn't match");
}

21


Binary Literals

• Currently Java supports only decimal, octal and
hexadecimal numeric literals.
• Java 7 supports also binary literals:

int a = 0b0101;
int b = 0b1010;
System.out.println(a+b);

21


Improved Type Inference

• While the Java compiler will not provide extensive type
inference (as in Scala), a minor inference improvement
is introduced in Java 7:

List<String> strings = new ArrayList<>();

21


Multi-Catch

• One of the annoying things about exception handling in
Java is the need to duplicate exception handling code
for different exception types.
• This is addressed in Java 7 as mulit-catch.

• Let’s see it in action:

21


Example

private static void f() throws SQLException {

}
private static void g() throws IOException {

}

private static void multicatch() {
try {
f();
g();
} catch (SQLException | IOException e) {
System.out.println("got either exception");

}

}

21


Precise Rethrow

• Currently the following code will not compile:

public void foo() throws IOException, SQLException {
try {
// do something that may throw IOException or
// SQLException
} catch (Exception e) {
// do something
throw(e);
}
}

29


Safe Re-throw

• The syntax to allow this is with the final keyword:

public void foo() throws IOException, SQLException {
try {
// do something that may throw IOException or
// SQLException
} catch (final Exception e) {
// do something
throw(e);
}
}

30


ARM

• Automatic Resource Management will allow you to
specify a resource (AutoClosable type) to use with the
try-catch block.
• When you exist the try-catch block the close() method
will be invoked automatically.

• Let’s see it in action…

21


Try with Resources

static class MyClass implements AutoCloseable {
@Override
public void close() throws Exception {
System.out.println("Close was called");

}
}

private static void trywith() {
MyClass resource1 = new MyClass();
MyClass resource2 = new MyClass();
try (resource1; resource2) {
System.out.println("in try");
} catch (Exception e) {
System.out.println("in catch");
}

}

29


Concurrency Utils

• Doug Lea, the founder of the excellent
java.util.concurrent introduces (through JSR 166) the
following new features:
• Fork/Join framework.
• TransferQueue.
• ThreadLocalRandom.
• Phasers.

18


Fork/Join

• The basic idea of the Fork/Join framework is that many
tasks can be split to several concurrent threads, and the
result should be merged back.

• Let’s take a look at an example…

19


Fork/Join

• Instead of doing it single-threaded, the idea of fork/join
is to split the operation to several (depends on the # of
cores) concurrent threads.

public class Fibonacci extends RecursiveTask<Integer> {
private final int n;

public Fibonacci(int n) { this.n = n;}
protected Integer compute() {
if (n <= 1)
return n;
Fibonacci f1 = new Fibonacci(n - 1);
f1.fork();
Fibonacci f2 = new Fibonacci(n - 2);
return f2.compute() + f1.join();
}
}

20


Example

• The Main class:

public class Main {
public static void main(String[] args) {
ForkJoinPool pool = new ForkJoinPool(3);
Fibonacci fibonacci = new Fibonacci(20);
pool.execute(fibonacci);
System.out.println(fibonacci.join());

}
}

21


TransferQueue

• A BlockingQueue on which the producers await for a
consumer to take their elements.
• Usage scenarios are typically message passing
applications.

22


Phasers

• “Beam me up, Scotty!”
• A Phaser is quite similar to CyclicBarrier and
CountDownLatch but is more powerful and flexible.
• A Phaser has an associated phase-number which is of
type int.
• A Phaser has a number of unarrived parties. Unlike
CyclicBarrier and CountDownLatch, this number is
dynamic.

23


Phasers

• A Phaser supports operations for
arriving, awaiting, termination, deregistration and
registration.
• When all the parties arrive, the Phaser advances
(increments its phase-number).
• Phasers also supports ForkJoinTasks!

24


NIO.2

• JSR 203 adds new APIs to the NIO package.
• Main features:
• Filesystem API.
• Asynchronous Channels.

25


Filesystem API

• At the heart of the new filesystem API stands the Path
class.
• An instance of Path can be thought of as an improved
version of a File instance.
• Also, File now provides a method for legacy code
named: toPath().

• Let’s explore this class…

26


Path

• Path is an abstract representation of an hierarchical
path from the filesystem provider.
• For regular filesystems, a Path is interoperable with File.
• For other providers (e.g., ZipFileSystemProvider) there
is no analogy.
• A Path instance also supports symbolic links and
provides the method: readSymbolicLink().

26


Path Methods

• Interesting methods:
• getRoot().
• isAbsolute().
• startsWith(), endsWith().
• normalize() – removes ‘..’ and ‘.’.
• copyTo() , moveTo().
• newByteChannel(), newOutputStream().

• And of-course, ‘watch’ methods.

26


Watchable

• Path implements the Watchable interface.
• This allows for registering watchers that are interested
in events on the Path.
• Example for events:
• OVERFLOW, ENTRY_CREATE, ENTRY_DELETE, ENTRY
_MODIFY.

• Let’s see an example for logging which files are deleted
on a given directory…

26


Example

FileSystem fs = FileSystems.getDefault();
WatchService ws = fs.newWatchService();

Path path = fs.getPath("c:todeletewatch");
path.register(ws, StandardWatchEventKind.ENTRY_DELETE);
while(true) {
WatchKey e = ws.take();
List<WatchEvent<?>> events = e.pollEvents();
for (WatchEvent<?> watchEvent : events) {
Path ctx = (Path) watchEvent.context();
System.out.println("deleted: " + path);
}
}

21


Not Included

• The following (promised) features were not included in
Java 7:
• Lambda and Closures.
• Refied Generics.
• Modularization.
• Annotations on Java types.
• Collections literals.

38


Java 8?

• So, what is intended for Java 8?
• Well, JSR 337 (Java 8) promises the following:
• Annotations on types.
• Lambdas.
• Parallel collections and support for lambdas in
collections.
• Date & time APIs.
• Module system.

38


Proposed Lambda Syntax

• Following is the current state of JSR 335 (Lambda
expressions for Java):

Lambda for Runnable

executor.submit( #{ System.out.println("Blah") } );

Collections.sort(people, #{ Person x, Person y ->
x.getLastName().compareTo(y.getLastName()
) });

38

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