GENERICS - Introduction to Java Programming: Comprehensive Version - page 757

20 GenericMatrix.printResult(
21 m1, m2, rationalMatrix.multiplyMatrix(m1, m2), '*' );
22 }
23 }

multiply two matrices

m1 + m2 is
1/5 1/6 1/7 1/6 1/7 1/8 11/30 13/42 15/56
2/5 1/3 2/7 + 1/3 2/7 1/4 = 11/15 13/21 15/28
3/5 1/2 3/7 1/2 3/7 3/8 11/10 13/14 45/56
m1 * m2 is
1/5 1/6 1/7 1/6 1/7 1/8 101/630 101/735 101/840
2/5 1/3 2/7 * 1/3 2/7 1/4 = 101/315 202/735 101/420
3/5 1/2 3/7 1/2 3/7 3/8 101/210 101/245 101/280

19.23

✓ ✓

Why are the add , multiple , and zero methods defined abstract in the
GenericMatrix class?

Check

Point

19.24

How are the add , multiple , and zero methods implemented in the
IntegerMatrix class?

19.25

How are the add , multiple , and zero methods implemented in the
RationalMatrix class?

19.26

What would be wrong if the printResult method defined as follows?

public static void printResult(
E[][] m1, E[][] m2, E[][] m3, char op)

K EY T ERMS

actual concrete type 738 generic instantiation 738

bounded generic type 743 lower-bound wildcard

( <? super E> )

bounded wildcard
( <? extends E> )

748

748 raw type 746

unbounded wildcard ( <?> ) formal generic type 738 748

C HAPTER S UMMARY
1.

Generics give you the capability to parameterize types. You can define a class or a
method with generic types, which the compiler replaces with concrete types.

2.

The key benefit of generics is to enable errors to be detected at compile time rather than
at runtime.

3.

A generic class or method permits you to specify allowable types of objects that the
class or method can work with. If you attempt to use a class or method with an incom-
patible object, the compiler will detect the error.

4.

A generic type defined in a class, interface, or a static method is called a formal generic
type , which can be replaced later with an actual concrete type . Replacing a generic type
is called a generic instantiation .