ABSTRACT CLASSES AND INTERFACES - Introduction to Java Programming - page 580

house1: House

Memory

id = 1
area = 1750.50
whenBuilt

1

1750.50

reference whenBuilt: Date

date object contents

house2 = house1.clone()

house2: House

Memory

id = 1
area = 1750.50
whenBuilt

1

1750.50

reference

F IGURE 15.6

The default clone method performs a shallow copy.

deep copy

To perform a deep copy for a House object, replace the clone() method in lines 26-27
with the following code:

public Object clone() throws CloneNotSupportedException {
// Perform a shallow copy
House houseClone = (House) super .clone();
// Deep copy on whenBuilt
houseClone.whenBuilt = (java.util.Date)(whenBuilt.clone());
return houseClone;

}

or

public Object clone() {
try {
// Perform a shallow copy
House houseClone = (House) super .clone();
// Deep copy on whenBuilt
houseClone.whenBuilt = (java.util.Date)(whenBuilt.clone());
return houseClone;

}
catch (CloneNotSupportedException ex) {
return null ;

}

}

Now if you clone a House object in the following code:

House house1 = new House( 1 , 1750.50 );
House house2 = (House)house1.clone();

house1.whenBuilt == house2.whenBuilt will be false . house1 and house2 refer-
ence two different Date objects.

15.22

Can you invoke the clone() method to clone an object if the class for the object
does not implement the java.lang.Cloneable ? Does the Date class imple-
ment Cloneable ?

✓ ✓

Check

Point

15.23

What would happen if the House class (defined in Listing 15.9) did not override the
clone() method or if House did not implement java.lang.Cloneable ?