USER-DEFINED CLASSES AND ADTS - Java Programming: From Problem Analysis to Program Design - page 479

Methods and Classes
Reference variables can be passed as parameters to methods and returned as method
values. Recall from Chapter 7 that when a reference variable is passed as a parameter to a
method, both the formal and actual parameters point to the same object.

Definitions of the Constructors and Methods
of the class Clock
We now give the definitions of the methods of the class Clock , then we will write the
complete definition of this class. First, note the following:
1. The class Clock has 11 methods: setTime , getHours , getMinutes ,
getSeconds , printTime , incrementHours , incrementMinutes ,
incrementSeconds , equals , makeCopy , and getCopy . It has two
constructors and three instance variables: hr , min , and sec .
2. The three instance variables— hr , min , and sec —are private to the
class and cannot be accessed directly outside the class .
3. The 11 methods— setTime , getHours , getMinutes , getSeconds ,
printTime , incrementHours , incrementMinutes , incrementSeconds ,
equals , makeCopy ,and getCopy —can directly access the instance vari-
ables ( hr , min ,and sec ). In other words, we do not pass instance
variables or data members as parameters to these methods. Similarly,
constructors directly access the instance variables.
Let's first write the definition of the method setTime . The method setTime has three
parameters of type int . This method sets the instance variables to the values specified by
the user, which are passed as parameters to this function. The definition of the method
setTime follows:

8

public void setTime( int hours, int minutes, int seconds)
{

if (0 <= hours && hours < 24)
hr = hours;
else
hr = 0;

if (0 <= minutes && minutes < 60)
min = minutes;
else
min = 0;

if (0 <= seconds && seconds < 60)
sec = seconds;
else
sec = 0;

}