USER-DEFINED CLASSES AND ADTS - Java Programming: From Problem Analysis to Program Design - page 495

The default definition of the method toString creates a string that is the name of the
object's class , followed by the hash code of the object. For example, in the preceding
statement, Clock is the name of the object myClock 's class and the hash code for the
object referenced by myClock is @11b86e7 .
The method toString is a public value-returning method. It does not take any parameters
and returns the address of a String object. The heading of the method toString is:

public String toString()

You can override the default definition of the method toString to convert an object to a
desired string. Suppose that for the objects of the class Clock you want the method
toString to create the string hh:mm:ss —the string consists of the object's hour, minutes,
seconds, and the colons as shown. The string created by the method toString is the same
as the string output by the method printTime of the class Clock . This is easily
accomplished by providing the following definition of the method toString :

public String toString()
{

String str = "";

if (hr < 10)
str = "0";
str = str + hr + ":";

8

if (min < 10)
str = str + "0" ;
str = str + min + ":";

if (sec < 10)
str = str + "0";
str = str + sec;

return str;

}
In the preceding code, str is a String variable used to create the required string.
The preceding definition of the method toString must be included in the class
Clock . In fact, after including the method toString in the class Clock , we can
remove the method printTime . If the values of the instance variables hr , min , and sec
of myClock are 8 , 25 , and 56 , respectively, then the output of the statement:

System.out.println(myClock)

is:

08:25:56
You can see that the method toString is useful for outputting the values of the instance
variables. Note that the method toString only returns the (formatted) string; the methods
print , println ,or printf output the string.