Lecture 8A

Question 1

A generic class name should always be noted together with…

Answer 1

…the ie MyClass

Question 2

Java compiler can show you error with generics, when?

Answer 2

Before runtime.

Question 3

What are benefits of using generics?

Answer 3

Increase type safety. Avoid type casts and code duplication. Also many runtime errors become compile time errors, checked statically.

Question 4

What are type bounds?

Answer 4

They restrict range of type parameters. Ie class myGen… This means any type T must extend OR implement type Sup.

Question 5

What is type erasure?

Answer 5

When the Java compiler translates generics into ordinary code after type checking.

Question 6

In generics what is a wildcard?

Answer 6

? Is a wildcard. Used in generics in methods: void myMethod(MyGenericClass> arg)
It stands for unknown type.
Can also use bounds: extends, super. Can also be used for return values.

Question 7

What is convariance?

Answer 7

Convariant arrays would be where Employee is a subclass of Person, Person[] array = new Employee[5]

Question 8

Why are Java generics not convariant?

Answer 8

To avoid runtime issues, ie Person[] array = new Emp[5]; array[0] = new Student(); compiles fine but error at runtime.

Question 9

Java generics are invariant?

Answer 9

Yes, ArrayList is NOT a subclass of ArrayList.

Question 10

What are generic static methods?

Answer 10

They use the static keyword and type parameters (not the wildcard ?): static void methodName(T[ ] a, Collection c){…}

Question 11

How can generic static methods be used?

Answer 11

Regardless of whether the class in which it’s declared is generic. Also, when a generic method is used it is NOT required to provide a concrete type for type parameter.

Question 12

What is the type parameter? And type argument? And type variable?

Answer 12

class MyClass {}

When making object from class:
MyClass myO = new MyClass(); String here is type argument. Inside class typeparameter is a type variable.