Question

What is the difference between the following 2 method signature:

public <T extends MyClass> Set<T> getMyList() {...}

public Set<? extends MyClass> getMyList() {...}

Answer 1

For first one you can use it as:

Set<MyClass> set = thing.getMyList();
Set<MyDerivedClass> set = thing.getMyList();
Set<?> set = thing.getMyList();
Set<? extends MyClass> set = thing.getMyList();
Set<? extends MyDerivedClass> set = thing.getMyList();

For the second, you are more limited:

Set<?> set = thing.getMyList();
Set<? extends MyClass> set = thing.getMyList();

How would you expect to implement the first? The second is bad because it forces client code to use wildcards.