WEEK 3 - INHERITANCE AND DEBUGGING PROGRAMS

Question 1

What is the subclass?

Answer 1

It is a class based on an existing class (the superclass). It is more specific than the superclass.

Example.
“circle” is more specific than “shape”

Question 2

What is the superclass?

Answer 2

It is an existing and generalized class compared to the subclass.

Example.
“shape” is more specific than “circle”

Question 3

What does a subclass inherit from the superclass?

Answer 3

All fields and methods.

Question 4

How can methods be overridden?

Answer 4

The subclass can create a method with the same name as another method in the superclass. This version of the method will override/replace the method from the superclass.

Question 5

What keyword is used to create/declare a subclass in Java?

Answer 5

extends.

Example.
public class Circle extends Shape {
private Point _center;
private double _radius;
public void draw() {…}
}

Question 6

What are some of the benefits of inheritance?

Answer 6

1. One superclass can be used to make many subclasses.
2. Reusability within the code.
3. Improves the structures of large programs (hierarchical).
4. Modular programming (encapsulation).

Question 7

What is a subclass capable of?

Answer 7

Inheriting from a superclass, it can override methods and add new properties and new methods.

Question 8

How many superclasses can there be?

Answer 8

One.

Question 9

How do you call the superclass version of an overridden method?

Answer 9

Using the super keyword.

Example.
super.draw()

**You can NOT override private methods

Question 10

Can you override field variables?

Answer 10

No, as it causes confusion and nasty bugs.

Question 11

A subclass has access to what?

Answer 11

All non-private fields and methods.

Question 12

What does protected mean?

Answer 12

A field or variable is visible to subclasses without making it public.

Question 13

Are superclass’s Constructor inherited?

Answer 13

No. They are invoked explicitly (using the super keyword) or implicitly (automatically invoked).

Question 14

You must use the keyword super to call the superclass
constructor. Invoking a superclass constructor’s name in a subclass causes which error?

Answer 14

Syntax.

Question 15

What signature must be added on all overrides?

Answer 15

@Override

It is usually put on a separate line. Compiler will give a syntax error if an override doesn’t occur.

Question 16

What is the final modifier?

Answer 16

The final modifier can be used on classes and class members (data and methods) except that the final modifier can also be used on local variables in a method. A final local variable is a constant inside a method.

FINAL CLASSES AND METHODS CANNOT BE EXTENDED AND OVERRIDDEN.

Question 17

Why is the String class final?

Answer 17

The String class is immutable and that means that the object state (field variables) cannot be changed after creation.

Question 18

What are the two major types of errors?

Answer 18

Syntax and runtime.

Question 19

What are syntax errors?

Answer 19

Always caught by the compiler, they are almost always easier to fix than runtime errors.

Question 20

What are runtime (logic) errors?

Answer 20

Discovered by testing, can be much harder to tell why the error/bug is happening.