Classes Revisited - Learning Java Through Games - page 182

name = "Superwoman"
address = 2000

name = "Superwoman"
address = 2000

location: 2000

object c2

object c1

streetName = "Main"
number = 123

object address

FIGURE 8.7: Cloning example.

public String toString() {
return number+ "" +streetName ;
} public void changeAddress(String streetName , int number) {
this . streetName = streetName ;
this . number = number ;

}

}

public class CloneTest {
public static void main(String [] args) throws Exception {
Address address = new Address( "Main" ,123) ;
FictionalCharacter c1 = new FictionalCharacter( "Superwoman" ,
address) ;
FictionalCharacter c2 = (FictionalCharacter) c1. clone() ;
address . changeAddress( "Main" , 235) ;
System. out . println (c2) ;

}

}

Figure 8.7 depicts what happens. We call super.clone() to perform the cloning of our
fictional character object. However, the default clone method inside the Object class does
not know anything about the structure of an object of type FictionalCharacter .Itsimply
copies all the data. As a result, both c1 and c2 will contain the same object of type Address .
Now, if this address is modified, the change will affect both objects.

Shallow copy happens when we copy the data of an object, but we do not make
copies of the inner objects. Shallow copy is dangerous because changes to an inner
object of one class leads to changes of the same inner object of the other class. The
default clone method inside the Object class performs shallow copy. If we want to
perform deep copy, we need to override the method.