Classes - Building Java Programs: A Back to Basics Approach - page 513

The toString Method
The designers of Java felt that it was important for all types of values to work well
with String s. You've seen that you can concatenate String s with any other type of
value, such as primitive int s or other objects. Consider the following code:
int i = 42;
String s = "hello";
Point p = new Point();
System.out.println("i is " + i);
System.out.println("s is " + s);
System.out.println("p is " + p);
Using the Point class that we've written so far, the preceding code produces out-
put like the following:
i is 42
s is hello
p is Point@119c082
Notice that printing p generated a strange result. We'd rather have it print the
object's state of (0, 0), but Java doesn't know how to do so unless we write a special
method in our Point class.
When a Java program is printing an object or concatenating it with a String , the
program calls a special method called toString on the object to convert it into a
String . The toString method is an instance method that returns a String repre-
sentation of the object. A toString method accepts no parameters and has a String
return type:
public String toString() {
<code to produce and return the desired string>;
}
If you don't write a toString method in your class, your class will use a default
version that returns the class name followed by an @ sign and some letters and num-
bers related to the object's address in memory. If you define your own toString
method, it replaces this default version.
The following code implements a toString method for our Point objects and
returns a String such as "(0, 0)" :
// returns a String representation of this point
public String toString() {
return "(" + x + ", " + y + ")";
}