USER-DEFINED CLASSES AND ADTS - Java Programming: From Problem Analysis to Program Design - page 513

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;

}

In the method setTime , the statement:

hr = hours;
is, in fact, equivalent to the statement:

this .hr = hours;

8

In this statement, the reference this is used explicitly. You can explicitly use the
reference this and write the equivalent definition of the method setTime as follows:

public void setTime( int hr, int min, int sec)
{

if (0 <= hr && hr < 24)
this .hr = hr;
else
this .hr = 0;

if (0 <= min && min < 60)
this .min = min;
else
this .min = 0;

if (0 <= sec && sec < 60)
this .sec = sec;
else
this .sec = 0;

}

Notice that in the preceding definition of the method setTime , the name of the formal
parameters and the name of the instance variables are the same. In this definition of the
method setTime , the expression this .hr means the instance variable hr , not the formal
parameter hr , and so on. Because the code explicitly uses the reference this , the
compiler can distinguish between the instance variables and the formal parameters. Of