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New features in Java 7

September 27, 2012 at 10:37 pm | blog, general | No comment

 

Here’s a summary of the most exciting features of the upcoming Java 7, which is of interest for the Java community and, consequently, for Android developers!

Language enhancements

Left to right type inference

This basically allows you to write Map<String, List<String>> retVal = new HashMap<>(); instead of Map<String, List<String>> retVal = new HashMap<String, List<String>>();, which is unnecessarily verbose.

It also infers the type of the return type: in a method whose signature is Map<String, List<String>> parseSomething() you can just return new HashMap<>(); and have the generics information inferred.

Using strings in switch statements

A natural extension of the switch statement. No longer do we have to map those strings to integers or enums, or write error-prone anidated if statements. It’s also a bit more efficient. For details see the Compilation section in the initial proposal.

Automatic resource management

Not much ago, we spent quite some time tracking down a bug because some DB connections were not closed. In complex infraestructures (i.e., where you use Spring, define several aspects to AspectJ, but sometimes you also program at the low level for optimization purposes), this is not always a trivial topic. Making sure you free this type of resources will no longer be necessary.

With Java 7, you can write

try (InputStream is = new FileInputStream(new File("foo.txt"))) {
    // read the file and do something with it
} catch (IOException e) {
    // handle this
}

instead of the more verbose, error-prone:

InputStream is = null;
try {
    is = FileInputStream(new File("foo.txt"));
    // read the file and do something with it
} catch (IOException e) {
    // handle this exception
} finally {
    if (is != null) {
        try {
            is.close();
        } catch (IOException ex) {
            // ignore this exception
        }
    }
}

You can thank the java.lang.AutoClosable interface, that has just one method: void close() throws Exception;.

Improvements to literals

Underscores: now you can write int billion = 1_000_000_000; instead of int billion = 1000000000; in order to make sure you don’t miscount the 0s.

Binary literals: this is an obvious extension to the literals, now you can write int yourInteger = 0b100100101; // 293 in decimal.

Improved exception handling

It’s common (and not necessarily a bad sign) to deal with different exception types in the same way. Instead of duplicating code by copy-pasting the same exception routine, now we can use the OR (\|) operator to group the exceptions:

try {
    methodThatThrowsThreeExceptions();
} catch (ExceptionOne e) {
    // deal with ExceptionOne
} catch (ExceptionTwo | ExceptionThree e) {
    // deal with ExceptionTwo and ExceptionThree, even if they belong to different hierarchies
}

Somewhat related to this is the ability to rethrow exceptions with their original types, with no wrapping, and without the need to catch them separately. The following piece of code, valid in Java 7,

private void throwExceptions() throws A, B, C {
    try {
        // some operation that's declared to throw A, B or C exceptions
    } catch (Exception e){
        LOGGER.error("Caught " + e + " and rethrowing it", e);
        throw e;
    }
}

is exactly equivalent to

private void throwExceptions() throws A, B, C {
    try {
        throwAccordingToIndex(new Random().nextInt(2));
    } catch (A e){
        LOGGER.error("Caught " + e + " and rethrowing it", e);
        throw e;
    }
    catch (B e){
        LOGGER.error("Caught " + e + " and rethrowing it", e);
        throw e;
    }
    catch (C e){
        LOGGER.error("Caught " + e + " and rethrowing it", e);
        throw e;
    }
}

You could argue that you should be using AOP here for the instrumentation of this exceptions, but that’s another topic.

New I/O API version (NIO.2)

You’ve probably had issues at some point in time with working with absolute/relative paths, especially for programs that run in different operating systems. Also, deleting/renaming files lead to issues, as it did working with symbolic links. This version aims at making these uses cases easier.

Path

The class java.nio.file.Path will probably become the most commonly used in this package. It’s a substitute of our beloved java.io.Path, but better. You can do FileSystems.getDefault().getPath("hello.txt");, or Paths.get("file.data").getParent();. It’s basically simpler to use, especially in an environment with different filesystems.

Files

This utility class provides over 50 utility methods, such as copy(), move(), newInputStream(), readAllBytes(), createSymbolicLink(), …

Watch Service API

This new API lets you listen to some system events related to files and directories, such as when a new file is created in a directory. For details, check out the javadoc of the WatchService.

Fork and Join

The fork/join framework helps you make effective use of current architectures with many cores. It is an implementation of the well known ExecutorService, that uses a work-stealing algorithm to make sure that no worker threads idle by stealing tasks from those that are busy.

It seems fairly easy to use as long as you have a good way of splitting your processing needs into smaller tasks. There is a very handy guide in this tutorial by Oracle.

Dynamism

This does not affect us directly, but it’s a nice addition for the Java Virtual Machine, to which we are seriously tied to.

More and more dynamically typed languages want to leverage the JVM, but they are limited by the fact that the JVM was conceived to be statically typed, which implies that the type information is only checked at compile time, and thus the JVM executes this strongly-typed bytecoded without caring about the type information. This is a limitation for the dynamically typed languages where the type information is unresolved until runtime. A new feature, named invokedynamic, has been introduced in java.lang.invoke, which will allow to create performant, high quality implementations of such languages easier.

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