Cast issue (when using generics)

[Robert Merwe]

Given the code below, I get the following compiler error: Type mismatch: cannot convert from Object to String
What I don't understand, is why the compiler is unable to resolve T to String in this case (by simply removing <X> (which isn't used), or eg declaring newShape as Shape<Integer> all works fine)

public class Shape <X>
{
	 public <T> T doStuff(T x)
	{
      	 return x;
	}
	 
	public static void main(String[] args) 
    {	 
   	 Shape newShape = new Shape();	 
   	 String x = newShape.doStuff("abcdef");
   	 System.out.println(x);
    }
}

[Ernest Friedman-Hill]

Hi Robert,

Welcome to JavaRanch!

That's an interesting observation, and I don't have a ready explanation for it. I suspect the answer is to be found in this section of the language spec, but only with a lot of heavy lifting:

http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#341287

[Rob Spoor]

Apparently when you drop generics in the declaration, it drops generics completely. Not just the class' generic types but also the method generic types. If you change the declaration in the easiest thing (Shape<?> newShape = ...) it works again.