Sunday, May 15, 2011

New On Java 7

Following are some of the things new on Java 7. Taken from various java documentations.

Catching More Than One Type of Exception with One Exception Handler

In Java SE 7 and later, a single catch block can handle more than one type of exception. This feature can reduce code duplication and lessen the temptation to catch an overly broad exception.

In the catch clause, specify the types of exceptions that block can handle, and separate each exception type with a vertical bar (|):

catch (IOException|SQLException ex) {
throw ex;

Note: If a catch block handles more than one exception type, then the catch parameter is implicitly final. In this example, the catch parameter ex is final and therefore you cannot assign any values to it within the catch block.

Using Non-Reifiable Parameters with Varargs Methods

Generics in varargs
The compiler issues a warning "warning: [unchecked] unchecked generic array creation" when generics are passed as varargs. This warning could be suppressed with @SafeVarArgs annotation on the method, which would ensure that the method wouldn't perform any unsafe operation.
public static void main(String[] args) {
        compute(new HashMap(), 
new TreeMap());

    static void compute(Map... args) {
Using Strings in switch Statements
A switch works with the byte, short, char, and int primitive data types. It also works with enumerated types (discussed in Enum Types), the String class, and a few special classes that wrap certain primitive types: Character, Byte, Short, and Integer (discussed in Numbers and Strings).

In Java SE 7 and later, you can use a String object in the switch statement's expression.
public static int getMonthNumber(String month) {

int monthNumber = 0;

if (month == null) { return monthNumber; }

switch (month.toLowerCase()) {
case "january":    monthNumber =  1; break;
case "february":   monthNumber =  2; break;
case "march":      monthNumber =  3; break;
case "april":      monthNumber =  4; break;
case "may":        monthNumber =  5; break;
case "june":       monthNumber =  6; break;
case "july":       monthNumber =  7; break;
case "august":     monthNumber =  8; break;
case "september":  monthNumber =  9; break;
case "october":    monthNumber = 10; break;
case "november":   monthNumber = 11; break;
case "december":   monthNumber = 12; break;
default:           monthNumber =  0; break;

return monthNumber;
The String in the switch expression is compared with the expressions associated with each case label as if the String.equals method were being used.

Diamond syntax
Until Java 7, generic instances were created with
Map<Integer, String> map = new HashMap<Integer, String>();
In Java 7 only refernce requires type information and actual type could be without type information.
Map<Integer, String> map = new HashMap<>();

Binary literal and underscore in numeric literals
Binary values could be defined as
int number = 0b1100110; // decimal 102
Lengthy numeric values can be separated using underscores
long longnum = 28_06_86L;
long verylongnumber = 2334_7656_4503_3844L;
Automatic Resource Management
With the new Java 7 try block syntax, resources declared while defining the try block will automatically close when the control comes out of the try block.
try (BufferedReader reader = new BufferedReader(new FileReader(fileName))) {
while ((line = reader.readLine()) != null) {
         //do some work
    } catch (IOException ex) {