generics ch14

Question 1

what is generics

Answer 1

java allows class and method definitions that include parameters for types - these definitions are called generics

Generic programming with a type parameter enables code to be written that applies to any class

Question 2

copies of arrayList

Answer 2

deep copy is needed - clone method not good enough - it produces a shallow copy

In order to make a deep copy, it must be possible to make a deep copy of objects of the base type
Then a deep copy of each element in the ArrayList can be created and placed into a new ArrayList object

Question 3

the arraylist class is a parameterized class - what does this mean

Answer 3

It has a parameter, denoted by Base_Type, that can be replaced by any reference type to obtain a class for ArrayLists with the specified base type

class that needs another class as a parameter - is like a cookie cutter class - have type parameters - e.g. type Employee is the parameter

Question 4

generic constructors

Answer 4

public Class()

A constructor can use the type parameter as the type for a parameter of the constructor, but in this case, the angular brackets are not used
public Pair(T first, T second)

Question 5

instantiated generic class

Answer 5

Pair pair = new Pair(“Happy”, “Day”);

Question 6

can you use primitive types in generic class parameters

Answer 6

no - The type plugged in for a type parameter must always be a reference type
reference types include arrays
but now that Java has auto boxing - not a big restriction

Question 7

what are the places where an ordinary class name would be allowed but the type parameter wouldnt be allowed

Answer 7

In particular, the type parameter cannot be used in simple expressions using new to create a new object
For instance, the type parameter cannot be used as a constructor name or like a constructor:
T object = new T();
T[] a = new T[10];

Question 8

is the instantiation of a generic class be an array base type?

Answer 8

no
Arrays such as the following are illegal:
Pair[] a = new Pair[10];

Question 9

generic class with multiple type parameters

Answer 9

TwoTypePair

Question 10

what are the bounds for type parameters

Answer 10

• may be on a class name rather than an interface name
• Then only descendent classes of the bounding class may be plugged in for the type parameters

public class Two

Question 11

declaring generic methods

Answer 11

public static T genMethod(T[] a)

Question 12

invoking generic methods

Answer 12

String s = NonG.genMethod(c);

Question 13

inheritance with generic classes

Answer 13

Given two classes: A and B, and given G: a generic class, there is no relationship between G<a> and G<b></b></a>

This is true regardless of the relationship between class A and B, e.g., if class B is a subclass of class A
</b></a>