Language Enhancements and Features

Java 7: The Top 8 Features - Part 3

     

7. Improved type inference for generic instance creation


Java 5 introduced generics which enabled developers to write type safe collections. However, generics can sometimes be too verbose. Consider the following example where we are creating a Map of List of String.

 

With Java 5 and 6


Map<String, List<String>> retVal = new HashMap<String, List<String>>();

 

Note that the full type is specified twice and is therefore redundant. Unfortunately, this was a limitation of Java 5 and 6.

 

With Java 7

 

Java 7 tries to get rid of this redundancy by introducing a left to right type inference. You can now rewrite the same statement by using the <> construct.

 

Map<String, List<String>> retVal = new HashMap<>();

 

This does make the code a little less verbose. You can also use <> construct when returning a newly created object.

 

 

This, in my opinion, goes only half way. The full solution would have been a right to left full type inference.

 

Map map = new HashMap<String, String>();

 

The above would have made the code even less verbose. Though this enhancement can still be done in a later version.

 

#8 More new I/O APIs for the Java platform (NIO.2)

 

A new set of I/O APIs and features were introduced in Java 1.4 under the java.nio package. This addition was called the New I/O APIs, also known as NIO. Naming something New is always short-sighted because it will not remain new forever. When the next version comes along, what should the new version be called, the NEW NEW I/O? Java 1.7 offers a rich set of new features and I/O capabilities, called NIO.2 (New I/O version 2?). Here are the key highlights of NIO.2.

 

a) Package

 

The most important package to look for is java.nio.file. This package contains many practical file utilities, new file I/O related classes and interfaces.

 

b) The java.nio.file.Path interface

 

Path is probably the new class that developers will use most often. The file referred by the path does not need to exist. The file referred to does not need to exist. For all practical purposes, you can think of replacing java.io.File with java. io.Path.

 

Old Way


File file = new File("hello.txt");
System.out.println("File exists() == " + file.exists());

 

New Way


Path path = FileSystems.getDefault().getPath("hello.txt");
System.out.println("Path exists() == " + Files.exists(path));

 

c) The java.nio.file.Files class


The Files class offers over 50 utility methods for File related operations which many developers would have wanted to be a part of earlier Java releases. Here are some methods to give you a sense of the range of methods offered. • copy() – copy a file, with options like REPLACE_EXISTING, NOFOLLOW_LINKS public static Path copy(Path source, Path target, CopyOption... options);

 

move() – move or rename a file public static Path move(Path source, Path target, CopyOption... options);

 

newInputStream() – create input stream public static InputStream newInputStream(Path path, OpenOption... options);

 

readAllBytes() – similar to the Apache IOUtils.readFile-ToByteArray public static byte[] readAllBytes(Path path) throws IOException;

 

createSymbolicLink() – creates a symbolic link, if supported by the file system public static Path createSymbolicLink(Path link, Path target, FileAttribute<?>... attrs) throws IOException

 

 

d) WatchService API

 

WatchService API is a new feature introduced in Java 1.7. It provides an API that lets you “listen” to a certain type of file system events. Your code gets called automatically when those events occur. Examples of event types are captured by StandardWatchEventKinds class.

 

• ENTRY_CREATE:an entry is created or renamed in the directory

• ENTRY_DELETE:an entry is created or renamed out of the directory

• ENTRY_MODIFY:a directory entry is modified

 

Example

Here’s a full example of how to watch a directory and print any newly created files.

 

 

Run the above program. Then create a file ‘new.txt’ in the directory ‘logs’. The program will print:

logs: new file created new.txt

 

Note about WatchService implementation

 

The implementation will take advantage of native support for file change notification when supported by the native file system, but will resort to polling otherwise.

 

IDE Support

 

Java 7 support is now available in NetBeans and IntelliJ. Eclipse does not support Java 7 yet. The upcoming release of Eclipse 3.7 will not have support for Java 7 either, but support will be added in 3.7 SR1, expected September 2011 (table 2).

 

Conclusion

 

Java 7 offers many small language enhancements and features. However, I did not find any feature as compelling as Regex enhancement in Java 1.4 or Generics, Auto-boxing or Enum enhancement in Java 1.5. I find the try-with-resources enhancement particularly useful and am looking forward to using it. I also look forward to using new features from the NIO.2 library. Overall, I am glad that something was released this year as opposed to releasing a monolith of changes next year.

 


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Vineet  Manohar
Vineet Manohar

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