Exam 10: Inheritance and Polymorphism

The superclass inherits all its properties from the subclass.

To determine whether a reference variable that points to an object is of a particular class type, Java provides the operator instanceof.

Consider the following class definitions. public class BClass {private int x; public void set(int a) {x = a;} public void print() {System.out.print(x);}} public class DClass extends BClass {private int y; public void set(int a, int b) {//Postcondition: x = a; y = b;} public void print(){ }} Which of the following correctly redefines the method print of DClass? (i) public void print() {System.out.print(x + " " + y);} (ii) public void print() {super.print(); System.out.print(" " + y);}

A subclass can override public methods of a superclass.

Suppose that the class Mystery is derived from the class Secret. Consider the following statements. Secret mySecret = new Secret(); Secret secRef; Mystery myMystery = new Mystery(); Mystery mysRef; secRef = myMystery; Which of the following statements is legal in Java? (i) mysRef = (Mystery) mySecret; (ii) mysRef = (Mystery) secRef;

Suppose that the class Mystery is derived from the class Secret. The following statements are legal in Java. Secret secRef; Mystery mysRef = new Mystery(); secRef = mysRef;

A subclass inherits all its data members from the superclass; it has none of its own.

The classes Reader and Writer are derived from the class ____.

In Java, stream classes are implemented using the inheritance mechanism.

If a class implements an interface, it must ____.

Interfaces are defined using the reserved word interface and the reserved word class.

An abstract method is a method that has only the heading with no body.

In Java, polymorphism is implemented using late binding.

If class Dog has a subclass Retriever, which of the following is true?

A subclass can directly access protected members of a superclass.

What type of inheritance does Java support?

The class Object is directly or indirectly the superclass of every class in Java.

-Based on the diagram in the accompanying figure, which of the following members will Box NOT have direct access to?

An abstract class can contain ____.

A subclass can directly access ____.