Generics

Question 1

Why use generics?

Answer 1

To not limit the use of classes/methods to only one type.

Question 2

At which level can we use generics?

Answer 2

1. class-level generic
2. method-level generic

Question 3

What is an inner class and why to use one?

Answer 3

A class declared inside another class for:
- security (private classes)
- high-density modules (one class frameworks, can be esier to maintain for small projects)

Question 4

What are the types of inner classes?

Answer 4

1. nested inner classes
   (idealy private)
2. method-local inner class (cannot be private/protected/public/static)
3. anonymous inner classes(extending the inner class or implementing an interface in-place)

Question 5

How does class-level generics look like?

Answer 5

class MyCLass <T, U> {
private T t;
private U u;
…}
- this class has generic fields

Question 6

How does method-level generics look like?

Answer 6

public <T> void method(arguments 'can also be T')
- this method has generic arguments</T>

Question 7

How does a nested inner class look like?

Answer 7

class A{
public void useInnerA() {…\can use methods from innerA
}
(private) class InnerA {…}
}

Question 8

How does a method-local inner class look like?

Answer 8

class A{
public void doSth() {
class LocalInnerA {…}
} }

Question 9

How does an anonymous inner class look like?

Answer 9

class AnonymousA {…}
class A {…}

Question 10

How does type erasure work in generics?

Answer 10

The Java compiler replaces the “special parameter” with real types. That means List<Integer>, List<String> and List<List<String>> have the same type at run-time.</String></String></Integer>

Question 11

What does PECS refer to?

Answer 11

Aka. the get-put principle, it is a java idiom to manipulate variance while preserving types.