Java Reference
In-Depth Information
Exercise 2.77
The
String
class defines a
length
accessor method with the following
header:
/**
* Return the number of characters in this string.
*/
public int length()
so the following is an example of its use with the
String
variable
fullName
:
fullName.length()
Add conditional statements to the constructor of
Student
to print an error message if
either the length of the
fullName
parameter is less than four characters or the length of the
studentId
parameter is less than three characters. However, the constructor should still
use those parameters to set the
name
and
id
fields, even if the error message is printed.
Hint:
Use if statements of the following form (that is, having no
else
part) to print the error
messages.
if(
perform a test on one of the parameters
) {
Print an error message if the test gave a true result
}
See Appendix D for further details of the different types of if statements, if necessary.
Exercise 2.78
Challenge exercise
Modify the
getLoginName
method of
Student
so
that it always generates a login name, even if either the
name
or the
id
field is not strictly long
enough. For strings shorter than the required length, use the whole string.
2.22
Experimenting with expressions: the Code Pad
In the previous sections, we have seen various expressions to achieve various computations,
such as the
total + price
calculation in the ticket machine and the
name.substring(0,4)
expression in the
Student
class.
In the remainder of this topic, we shall encounter many more such operations, sometimes
written with operator symbols (such as “+”) and sometimes written as method calls (such as
substring
). When we encounter new operators and methods, it often helps to try out with dif-
ferent examples what they do.
The Code Pad, which we have briefly used in Chapter 1, can help us experiment with Java
expressions (Figure 2.6). Here, we can type in expressions, which will then be immediately
evaluated and the results displayed. This is very helpful for trying out new operators and
methods.
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