USER-DEFINED CLASSES AND ADTS - Java Programming: From Problem Analysis to Program Design - page 494

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FIGURE 8-14 Effect of constructors on objects

If the values passed to a class object do not match the parameters of any constructor,
and if no type conversion is possible, a compile-time error will be generated.

Classes and the Method toString
Suppose that x is an int variable and the value of x is 25 . The statement:

System.out.println(x);
outputs:

25
However, the output of the statement:

System.out.println(myClock);

is:

Clock@11b86e7
which looks strange. (Note that when you execute a similar statement, you are likely to
get a different but similar output.) This is because whenever you create a class , the Java
system provides the method toString to that class . The method toString is used to
convert an object to a String object. When an object reference is provided as a
parameter to the methods print , println , and printf , the toString method is called.