Object-Oriented Techniques - Java - page 291

Formatting Objects for Printing with toString()

Problem

You want your objects to have a useful default format.

Solution

Override the toString() method inherited from java.lang.Object .

Discussion

Whenever you pass an object to System.out.println() or any equivalent method, or in-
volve it in string concatenation, Java automatically calls its toString() method. Java
“knows” that every object has a toString() method because java.lang.Object has one
and all classes are ultimately subclasses of Object . The default implementation, in
java.lang.Object , is neither pretty nor interesting: it just prints the class name, an @ sign,
and the object's hashCode() value (see Overriding the equals() and hashCode() Methods ) .
For example, if you run this code:

public public class class ToStringWithout ToStringWithout {

int int x , y ;

/** Simple constructor */
public public ToStringWithout ( int int anX , int int aY ) {

x = anX ; y = aY ;

}

/** Main just creates and prints an object */
public

public static void main ( String [] args ) {

System . out . println ( new

static void

new ToStringWithout ( 42 , 86 ));

}

}

you might see this uninformative output:

ToStringWithout@990c747b