Re: Polymorphism in Java SE?

ram@zedat.fu-berlin.de (Stefan Ram) writes:


  Thanks for the answers so far!

  Why do I not write a custom method or class for this?

  I have this idea that teaching should go from the simple
  things to more advanced things. To me, /using/ objects of
  JAVA-SE classes is more simple than /declaring/ custom classes
  (eating is more simple than designing a dish and cooking it).

  Therefore, when I introduce objects and their properties,
  I have not yet introduced class or non-static method
  declarations: Most statements still go into the body of
  the static ?main? method.

  So, at this point, I would like to show how to /use/
  polymorphic designs, but not yet how to create a new
  design.

  ?DriverManager.getConnection()? might be of no use when used
  in isolation and a full JDBC client might be too large at this
  point.

  To use the parse() method of a NumberFormat (Eric)

http://download.java.net/jdk7/docs/api/java/text/NumberFormat.html#parse(java.lang.String,%20java.text.ParsePosition)

  , is very close to what I was looking for.

  I will also look into catching an IOException,
  Calendar.getInstance(), java.lang.Class.forName and
  newInstance and other suggestions.

  One example I already use, but which looks somewhat contrived
  and not like the solution of any real problem is:

( Math.random() > .5 ? System.out : "example" ).hashCode()

  This is simple: No containers, no declarations, just
  polymorphism. There is an expression for an object whose
  type is only known at run time and a verb ?hashCode?, which
  indeed has two completely different implementations in
  both cases. This is good so far.

  The problem is: This example makes no real sense: One can not
  imagine that one really needs this specific expression to
  solve any problem. So I am looking for something as simple and
  polymorphic as this but with more sense. Possibly I can use
  the abovementioned ?parse? verb for this.