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Re: Object message?

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Daniele Futtorovic wrote:
> Roedy Green allegedly wrote:
>> bob smith wrote, quoted or indirectly quoted someone who said :
>>> Can someone tell me why "message" is an Object here in javax.swing.JOptionPane?
>>> Why isn't it a String?
>
>> In general Object can let you pass any sort of information to
>> yourself, not just a string. It can be formatted data.  The
>> disadvantage is you must cast it to a String.

No, you mustn't, actually. That would defeat the purpose of the 'message' argument.

> Not quite, Roedy. Among other things, it can be any JComponent. And
> that's extremely useful.

The other things: an 'Icon', an array, a 'Component' (not just 'JComponent', per the docs), 
and of course, any ol' 'Object' via its 'toString()'.

Also, in general you cannot cast a reference to 'String'. Reference casts must adhere to 
http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.5.1

You can use 'String' conversion or a transformation method.

http://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.4
http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#valueOf(java.lang.Object)
http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html#toString()
et al.

As for the OP's question, IT'S IN THE JAVADOCS!

http://docs.oracle.com/javase/7/docs/api/javax/swing/JOptionPane.html

"message
"A descriptive message to be placed in the dialog box. In the most common usage, message is just a String or String constant. However, the type of this parameter is actually Object. Its interpretation depends on its type: ..."

Followed by an explanation of what it does for each type. So, no, you don't have to convert/transform the reference to a 'String', contrary to what was said upthread.

bob, you might not be aware of the full power of the Javadocs. The ones for 'JOptionPane' show a lot of 
that power. It's got class-level documentation, which you should go ahead and read after all, field (static 
constant) documentation, constructor documentation, method documentation, nested class 
documentation, and of course, package documentation through the 'javax.swing' package 
documentation. It's also got hyperlinked documentation, some of which in Swing's case seems to 
have gotten sparse and some of which is good.

Swing is a tricky package. First and foremost it's a UI-builder platform. I've used a bunch, such 
as OpenLook, and quite often they are messy, but creatively and purposefully so. It's also an API.
This means it speaks in two domains of discourse. Types in an API have members, but that's a 
different "containment" than a UI component exercises over another. The former is class 
membership and the latter is geometric enclosure, sort of.

So the method could have had a bunch of overloads, one for each different 'message' type (not to 
be confused with a 'messageType'), but that could lead to an explosion of methods, so they chose 
to stick with 'Object' and presumably reflectively work its display magic. As a UI component it has 
the luxury of time to examine its arguments, but you do lose the safety net of compile-time checks.

-- 
Lew

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Thread

Object message? bob smith <bob@coolfone.comze.com> - 2012-10-08 12:52 -0700
  Re: Object message? Arne Vajhøj <arne@vajhoej.dk> - 2012-10-08 15:58 -0400
  Re: Object message? Knute Johnson <nospam@knutejohnson.com> - 2012-10-08 13:00 -0700
  Re: Object message? Eric Sosman <esosman@comcast-dot-net.invalid> - 2012-10-08 16:13 -0400
  Re: Object message? Roedy Green <see_website@mindprod.com.invalid> - 2012-10-09 02:11 -0700
    Re: Object message? Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-10-09 23:46 +0200
      Re: Object message? Lew <lewbloch@gmail.com> - 2012-10-09 16:01 -0700

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