Generic methods

[andre1011]

How can I have a generic method return a primitive data type such as an 'int' ?
I am just counting the number of elements in an array and returning that value as an integer

[Fubarable]

What's the problem? Why can't you just use return type of int? Am I missing something here?

For e.g.,

public class Fubar3
{
  public static <U> int myMethod(U[] u)
  {
    return u.length;
  }
  
  public static void main(String[] args)
  {
    String[] strings = {"uno", "dos", "tres"};
    
    System.out.println(myMethod(strings));
  }
}

myMethod returns an int with ease.

[andre1011]

It did not work at first but now it works like magic,
Thank You!

[Fubarable]

Hm, I don't know why it didn't work and now it does, nor do I know if I did anything other than wave my magic Java wand, but you're welcome.

[Eranga]

Hm, I don't know why it didn't work and now it does, nor do I know if I did anything other than wave my magic Java wand, but you're welcome.

Yep, it wont be a magic at all. :p

andre1011, compare your code with what Fubarable post in his first replay here in this thread. May be you have miss something.

[Steve11235]

So, Fubarable's code specifies that U is an unspecified Type; U[] allows any sort of array. This seems to have the same effect as simply declaring the parameter as Object[]. Is that true?

[DarrylBurke]

In this case, yes, the parameter could be declared as Object[]. But. If the class is generic, type-safety will be enforced at compile time.

A minor change to Fu's code:

public class Fubar3<U>
{
  public int myMethod(U[] u)
  {
    return u.length;
  }
  
  public static void main(String[] args)
  {
    String[] strings = {"uno", "dos", "tres"};
    
    new Fubar3<String> fubar3 = new Fubar3<String>();
    System.out.println(fubar3.myMethod(strings));

    Integer[] ints = {1, 2, 3};
    System.out.println(fubar3.myMethod(ints)); // compile time error
  }
}

Don't know whether I made things more obscure.

There are two Generics tutorials on the Sun site, elementary and advanced. And the relevant section in the JLS is also worth reading.

db

[Steve11235]

Thanks, DB. What you did is what I'm used to. I was under the impression that generic types had to be defined at the class level, as you showed. Then, a specific implementation of that class can specify a Type, which will be enforced.

I hadn't seen a generic defined, as opposed to referenced, in a method signature before. I'm not sure I see an value in that approach...