Classes - Building Java Programs: A Back to Basics Approach - page 514

Now that our class has this method, the preceding client code produces the following
output.
i is 42
s is hello
p is (0, 0)
Note that the client code didn't explicitly call the toString method; the compiler
did it automatically because the Point object was being concatenated with a String .
The toString method is also implicitly called when printing an object by itself, as
in the following code:
System.out.println(p);
In order for this implicit calling behavior to work properly, your toString
method's signature must exactly match the one shown in this section. Changing the
name or signature even slightly (for example, naming the method ToString with a
capital T, or convertToString ) will cause the class to produce the old output (e.g.,
" Point@119c082 " ). The reason has to do with concepts called inheritance and over-
riding that we will explore in the next chapter.
It is also legal to call toString explicitly if you prefer. The following client code
uses an explicit toString call and produces the same output as the original client
code:
System.out.println("p is " + p.toString());
Sun's Java guidelines recommend writing a toString method in every class you
write.
Common Programming Error
println Statement in toString Method
Since the toString method is closely related to printing, some students mistak-
enly think that they should place println statements in their toString meth-
ods, as in the following method:
// this toString method is flawed;
// it should return the String rather than printing it
public String toString() {
System.out.println("(" + x + ", " + y + ")");
return "";
}
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