Presents your 
JAVA E-NEWSLETTER for November 4, 2002

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CONTROL OUTPUT WITH MESSAGEFORMAT

Printf was a favorite tool that many C programmers sorely missed when
they moved to Java. Java had a replacement method, but it did not 
follow the same concepts as the printf() function in C.

Fortunately, the early Java library developers had seen fit to create a
tool that suited Java better than a printf function.

MessageFormat allows a developer to control the formatting of variables
in output text. It is a powerful class, as the following example shows:

String message =
    "Once upon a time ({1,date}, around about {1,time,short}), there " 
+
    "was a humble developer named Geppetto who slaved for " +
    "{0,number,integer} days with {2,number,percent} complete user " +
    "requirements. ";

Object[ ] variables =
    new Object[ ] { new Integer(4), new Date( ), new Double(0.21) }

String output = MessageFormat.format( message, variables );

System.out.println(output);

Hidden in the message is a little language that describes the 
formatting
of the output. An example output is shown below:

Once upon a time (Nov 3, 2002, around about 1:35 AM), there was a humble
developer named Geppetto who slaved for 4 days with 21% complete user
requirements.

If the same message wants to be pushed out again and again with
different variables, then a MessageFormat object can be built and given 
the message. Here's a modification of the above example:

//    String output = MessageFormat.format( message, variables );
//    becomes:

      MessageFormat formatter = new MessageFormat(message);
      String output = formatter.format(variables);

In addition to handling dates, times, numbers, and percentages,
MessageFormat also deals with currencies, allows more control over the 
number format, and allows ChoiceFormats to be specified.

MessageFormat is a neat class that probably doesn't get used as often as
it should. Its biggest drawback is in wanting data to be passed in as a
variable and not as a Properties object. One simple way to solve this
would be a wrapper that preparsed the String to be formatted, turning 
the Properties key into an array index, for the ordering that 
Properties.keys(
) returns.

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