ABSTRACT CLASSES AND INTERFACES - Introduction to Java Programming: Comprehensive Version - page 517

13.22

✓ ✓

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 implement
Cloneable ?

Check

Point

13.23

What would happen if the House class (defined in Listing 13.11) did not override the
clone() method or if House did not implement java.lang.Cloneable ?

13.24

Show the output of the following code:

java.util.Date date = new java.util.Date();
java.util.Date date1 = date;
java.util.Date date2 = (java.util.Date)(date.clone());
System.out.println(date == date1);
System.out.println(date == date2);
System.out.println(date.equals(date2));

13.25

Show the output of the following code:

ArrayList<String> list = new ArrayList<>();
list.add( "New York" );
ArrayList<String> list1 = list;
ArrayList<String> list2 = (ArrayList<String>)(list.clone());
list.add( "Atlanta" );
System.out.println(list == list1);
System.out.println(list == list2);
System.out.println( "list is " + list);
System.out.println( "list1 is " + list1);
System.out.println( "list2.get(0) is " + list2.get( 0 ));
System.out.println( "list2.size() is " + list2.size());

13.26

What is wrong in the following code?

public class Test {
public static void main(String[] args) {
GeometricObject x = new Circle( 3 );
GeometricObject y = x.clone();
System.out.println(x == y);
}
}

13.8 Interfaces vs. Abstract Classes
A class can implement multiple interfaces, but it can only extend one superclass.

Key
Point

An interface can be used more or less the same way as an abstract class, but defining
an interface is different from defining an abstract class. Table 13.2 summarizes the
differences.

T ABLE 13.2

Interfaces vs. Abstract Classes

Variables Constructors Methods

Abstract class No restrictions. Constructors are invoked by subclasses through

constructor chaining. An abstract class cannot be
instantiated using the new operator.

No restrictions.

Interface All variables must be

public static final .

No constructors. An interface cannot be instantiated
using the new operator.

All methods must be public
abstract instance methods