Java Programming Chapter 11 Quiz

Questions and Answers

Object-oriented programming allows you to derive new classes from existing classes. This is called __________.

inheritance

Which of the following statements are true? (Choose more than one)

"class A extends B" means B is a subclass of A.

A subclass is usually extended to contain more functions and more detailed information than its superclass. (correct)

A subclass is a subset of a superclass.

"class A extends B" means A is a subclass of B. (correct)

What is the output of the following code? public class Test1 { public static void main(String[] args) { ChildClass c = new ChildClass(); c.print(); } } class ParentClass { int id = 1; void print() { System.out.println(id); } } class ChildClass extends ParentClass { int id = 2; }

Analyze the following code: class Square extends GeometricObject { double length; Square(double length) { GeometricObject(length); } } What is true?

The program has a compile error because you attempted to invoke the GeometricObject class's constructor illegally. Signup and view all the answers

Analyze the following code: public class A extends B { } class B { public B(String s) { } } (Choose more than one)

The program has a compilation error because the default constructor of A invokes the default constructor of B, but B does not have a default constructor. Signup and view all the answers

Analyze the following code: public class Test extends A { public static void main(String[] args) { Test t = new Test(); t.print(); } } class A { String s; A(String s) { this.s = s; } public void print() { System.out.println(s); } } (Choose more than one)

The program has an implicit default constructor Test(), but it cannot be compiled, because its superclass does not have a default constructor. Signup and view all the answers

What is the output of running class C? class A { public A() { System.out.println("The default constructor of A is invoked"); } } class B extends A { public B() { System.out.println("The default constructor of B is invoked"); } } public class C { public static void main(String[] args) { B b = new B(); } }

The default constructor of A is invoked; The default constructor of B is invoked Signup and view all the answers

Which of the following is incorrect?

A constructor may be static. Signup and view all the answers

Study Notes

Object-Oriented Programming Concepts

Object-oriented programming supports the creation of new classes from existing classes, a process known as inheritance.
A subclass is typically enhanced with more functionality and detail than its superclass.

Constructor Mechanics

In Java, the statement class A extends B signifies that A is a subclass of B.
If a subclass does not define a constructor, the default constructor attempts to call its superclass’s default constructor. If the superclass lacks a default constructor, a compilation error occurs.

Code Behavior and Output

In a code example with overlapping variable names in subclasses, the method in the superclass is utilized. Thus, when calling print() from ChildClass, the output will reflect the ParentClass variable scope, displaying the parent's id.
The incorrect invocation of a superclass constructor may lead to compilation errors, emphasizing the importance of constructor chaining.

Common Compilation Errors

Attempting to invoke an unknown or unsupported constructor results in a compile-time error. If constructor signatures do not match, the Java compiler will flag this as an issue.
To resolve errors related to constructors, ensure that subclasses correctly call the superclass constructors using super().

Constructor Characteristics

Constructors cannot be declared as static; they must be instance methods.
Private constructors can restrict instance creation, often used in singleton patterns.
Constructors can call other constructors (overloaded ones) within the same class or through superclass constructors using this() or super() respectively.

Execution Flow

When an instance of a subclass is created, the superclass's constructor runs first, initializing inherited fields before the subclass's constructor executes. This results in cascading constructor calls.

General Misconceptions

Some statements about constructors are incorrect; it is essential to understand their capabilities and limitations to avoid logical errors in Java programs.

Description

Test your knowledge of object-oriented programming concepts from Chapter 11 of 'Intro to Java Programming, Ninth Edition'. Focus on key terms such as inheritance and subclass relationships. This quiz includes multiple-choice questions to reinforce your understanding.