The Java Language changes accepted for inclusion in JDK7 have been announced by Joseph Darcy. We already knew that closures were off the menu. So too, unfortunately, is language support for arbitrary-precision arithmetic. The final list is pretty non-controversial and includes a number of changes that will reduce the verbosity of Java programs (one of the main criticisms of Java from proponents of other languages). Java will never be as terse as Perl or Haskell, but that’s no bad thing. One of the strengths of Java is its readability. There are however some areas where the language is needlessly verbose and that’s what these changes are addressing.
Simplified Generics
The last major revision of the Java language was Java 5.0, which introduced generics, auto-boxing, enums, varargs and annotations. Despite the compromises of type erasure, generics have been a major improvement to the language. They have also contributed to the verbosity of Java code. The necessity to specify, in full, both the reference type and value type of a field or variable has led to some very long declarations:
Map<String, List<BigDecimal>> numberMap = new TreeMap<String, List<BigDecimal>>(); |
JDK7’s proposed diamond notation allows the programmer to omit the generic parameters on the righthand side if they are the same as the left:
Map<String, List<BigDecimal>> numberMap = new TreeMap<>(); |
Collection Literals
The long overdue addition of collection literals will help to reduce the size of Java code and make it more readable. Lists, sets and maps can be created and populated without the need for cumbersome instance initialisers:
List<Integer> powersOf2 = {1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024}; |
Map<String, Integer> ages = {"John" : 35, "Mary" : 28, "Steve" : 42}; |
Automatic Resource Management
Josh Bloch’s proposal for automatic resource management gives Java an alternative to C++’s RAII and C#’s using. It eliminates much of the boiler-plate exception handling that surrounds the proper creation and disposal of resources, such as IO streams, in Java code. The proposal introduces a new interface, Disposable, that resources will implement. The syntax of try/catch/finally is extended to allow resources to be specified at the start. These resources are then automatically disposed upon completion. Here’s an example of the new syntax in action (taken from the proposal):
static String readFirstLineFromFile2(String path) throws IOException { try (BufferedReader reader = new BufferedReader(new FileReader(path)) { return reader.readLine(); } } |
Other Changes
As well as the above changes to tackle verbosity, JDK7 adds binary integer literals and the ability use String literals in switch statements. JDK7 will also fix the problem of mixing varargs parameters with generic types.