Wednesday, May 30, 2012

java method taking a single argument but 2 alternative types

Requirement: method read() in an interface IReader needs to accept a single argument but of various types

read(Book b) to be implemented by one concrete class BookReader
read(Score s) to be implemented by another concrete class ScoreReader

Suppose we want to unify the 2 read() methods into one unified method, so a "client" can get an instance of Reader and simply pass in either a book or a score.

Solution 1: use Object argument

Solution 2: declare
<T> read(T content, Class<T> argumentClass);

BookReader.java implements
<T> read(T content, Class<T> argumentClass){
  if (content instanceof Book){....
}

Paradoxically IDE may warn you that argumentClass is an unused variable inside the method. However Compiler use it to enforce type safety --

   myReader.read(someBook, Integer.class);// won't compile. Book.class required

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