Question

Given the method definiton

public void foo(List<Object>) { ... }

What happens if you want to call

foo(new ArrayList<String>);

Answer 1

Based on your question above I deduce your foo method to be as follows

public void foo(List<Object> ob)

{

//Lines of code;

}

Now based on the method call you have shown there can be two cases I can deduce

1. foo(new ArrayList<String>);--- Without bracket after String

&

2.foo(new ArrayList<String>());-- With Bracket after String

I will tell you what will happen in both the cases, for the first case it will give the below error

error: '(' or '[' expected as you are missing the parenthesis after the constructor.

For the second case if there is the() bracket . We will still get an error

error: incompatible types: ArrayList cannot be converted to List

even though String is a sub-class of Object as in Generic type polymorphism is not allowed it is only applicable to collection types.

if it were foo(new ArrayList<Object>()); or foo(new ArrayList<? extends Object>()); both would have been valid and the program would have executed successfully.