Java Reference
In-Depth Information
2.21
Calling methods
The
getLoginName
method illustrates a new feature that is worth exploring:
public String getLoginName()
{
return name.substring(0,4) +
id.substring(0,3);
}
We are seeing two things in action here:
■
Calling a method on another object, where the method returns a result.
■
Using the value returned as a result as part of an expression.
Both
name
and
id
are
String
objects, and the
String
class has a method,
substring
, with
the following header:
/**
* Return a new string containing the characters from
* beginIndex to (endIndex-1) from this string.
*/
public String substring(int beginIndex, int endIndex)
An index value of zero represents the first character of a string, so
getLoginName
takes the
first four characters of the
name
string and the first three characters of the
id
string and then
concatenates them together to form a new string. This new string is returned as the method's re-
sult. For instance, if
name
is the string
"Leonardo da Vinci"
and id is the string
"468366"
,
then the string
"Leon468"
would be returned by this method.
We will learn more about method calling between objects in Chapter 3.
Exercise 2.74
Draw a picture of the form shown in Figure 2.3, representing the initial state
of a
Student
object following its construction, with the following actual parameter values:
new Student("Benjamin Jonson", "738321")
Exercise 2.75
What would be returned by
getLoginName
for a student with
name
"Henry Moore"
and
id "557214"
?
Exercise 2.76
Create a
Student
with name
"djb"
and
id "859012"
. What happens
when
getLoginName
is called on this student? Why do you think this is?
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