How to call a generic method?

Question

I have a method, <T> void method(T element,Collection<T> list) , I am able to call it as method("A",list) , where list can be List<String> or List<Object>

But fails if I call method(new Object(),list) where list is List<String>

Thanks in advance.

Answer 1

This example shows, that your List<String> is not List<Object> even while String IS-A Object . You should use generic wildcards:

<T> void method(T element,Collection<? extends T> list)

Answer 2

Looking at the method <T> void method(T element,Collection<T> list)

When using a generic method an appropriate T is found. If no such T exists then a compile time exception is thrown.

method("A",new List<String>)

• First argument "A" T can be anything between Object and String
• Second argument T can be anything between String and String since the generic argument is explicitly defined by List<String>

T is String

method("A",new List<Object>)

• First argument "A" T can be anything between Object and String
• Second argument T can be anything between Object and Object since the generic argument is explicitly defined by List<Object>

T is Object

method(new Object(),new List<String>)

• First argument new Object() T can be anything between Object and Object
• Second argument T can be anything between String and String since the generic argument is explicitly defined by List<String>

No T exists that simultaneously satisfies both