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Question 174

Given:

Which option fails?

Foo mark = new Foo ("Steve", 100);

Foo pair = Foo.twice ("Hello World!");

Foo percentage = new Foo("Steve", 100);

Foo grade = new Foo <> ("John", "A");

Correct Answer: A

The correct answer is that the code in option A will fail. The reason is that it attempts to assign an object of type Foo<Object, Object> to a variable of type Foo<String, Integer>. In Java, generic types are invariant, meaning that Foo<Object, Object> is not a subtype of Foo<String, Integer>, even if String and Integer are subtypes of Object. This results in a type mismatch error.

Discussion

jduarteOption: A

Answer A. Tested Type mismatch: cannot convert from Foo<Object,Object> to Foo<String,Integer>

steefaandOption: A

A is correct. Can't have different types on left and right side if not using super/extends on left side.

duydnOption: A

Answer is A. <Object, Object> cannot cast to <String, Integer>

WilsonKKerllOption: A

Answer is A. Tested.

Svetleto13Option: A

A,tested