Software Engineering for Students A Programming Approach

194 Chapter 14 ■ The basics
In a language without this facility, we are forced to map the days of the week onto
integers, so that 1 means Monday etc. But then we get no help from the compiler when
we write (correct) statements, such as:
int today;
today = 2;
or even the “illegal”
today = 0;
since today is an integer variable and therefore may be assigned any integer value.
SELF-TEST QUESTION
14.4 Make the case for user-defined types.
Enumerated types, such as the C++ facility described above, have their limitations. An
enumerated type can be declared, variables created, assignments and comparisons carried
out, but these are the only operations and we cannot create any more. For example, in
the above example one cannot write a method nextDay. Moreover different enums cannot
contain identical names. For example, we are prevented from writing:
enum Weekend {Saturday, Sunday};
because the names clash with those already in enum Day.
Arguably, if the language provides classes (Chapter 15) it does not need enums. In
fact the Java enum facility is almost a class.
14.14 ● Arrays
Composite data types allow the programmer to model structured data objects. The
most common aggregate data abstraction provided by programming languages is the
array: a collection of homogeneous elements (all elements of the same type) which may
be referenced through their positions (usually an integer) within the collection. Arrays
are characterized by the type of their elements and by the index or subscript range or
ranges which specify the size, number of dimensions and how individual elements of
the array may be referenced.
For example, the Java array definition shown below defines an array named table.
It is a one-dimensional array of integers with the subscript varying from 0 through 9.
In Java, subscripts always start at 0, betraying the C origins of the language as a language
close to machine instructions.
int table[] = new int[10];