Java Programming Chapter 11 Flashcards

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 a subset of a superclass.

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

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

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) { } }

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); } }

The program would compile if a default constructor A() { } is added to class A explicitly. 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

Inheritance allows new classes to be derived from existing classes, enabling code reusability and a hierarchical relationship between classes.
A subclass can contain more functions and detailed information than its superclass, enhancing functionality.
The syntax "class A extends B" indicates that class A is a subclass of class B.

Code Output Analysis

In a Java program with a child and parent class, the output might show only the parent class attribute if the child class does not override it.
Constructor calls must be properly defined; failing to invoke a superclass's constructor correctly leads to compilation errors.

Constructor Behavior

A class without a default constructor will result in a compilation error if its superclass lacks a default constructor as well.
To resolve constructor issues, explicit constructors must be defined or superclass constructors invoked correctly using super().

Compiling and Runtime Errors

Java programs can compile but lead to runtime errors if the class structure or method invocation is mismanaged.
Ensure that constructors in subclasses correctly call their superclass constructors to avoid implicit default constructor issues.

Java Constructors

Constructors can be private but cannot be static, which restricts their behavior in altering the usual instance creation process.
Constructors can invoke other overloaded constructors within the same class, enabling flexible object initialization.

Output of Constructor Invocations

When an object of a subclass is created, constructors of both the subclass and its superclass are invoked, with the superclass constructor executing first. This is key to understanding the instantiation process and the relationship between class constructors.

Description

Test your knowledge of key concepts in object-oriented programming through these flashcards. This quiz focuses on inheritance, subclasses, and more as covered in Chapter 11 of 'Intro to Java Programming, Ninth Edition'.