Chapter 7 - Inheritance

Question 1

inheritance

Answer 1

• define a new class (subclass) in terms of how it extends an existing base class (superclass)
• using keyword ‘extends’

Question 2

runtime type vs. compile-time (static) type

Answer 2

• runtime: mentioned in new operation and represented by object returned by method getClass(); remains unchanged
• static type: type of variable in which a reference to the object is stored

Question 3

downcasting

Answer 3

• use instanceOf or getClass() before downcasting a variable

Question 4

single inheritance

Answer 4

• a given class can only declare to inherit from a single class
• by default, classes extend Object class

Question 5

inheriting fields

Answer 5

• when creating a new object, the object will have a field for each field declaration in its superclasses
• for fields to be accessible to subclasses, set their access modifiers to protected or use a getter method

Question 6

inheriting methods

Answer 6

• methods of a superclass are applicable to instances of a subclass
• can override methods
• can use super keyword to call method from superclass

Question 7

abstract classes

Answer 7

• cannot be instantiated
• can have both abstract (no implementation) and regular methods

Question 8

TEMPLATE METHOD design pattern

Answer 8

• put all common code in the superclass and define some hooks to allow subclasses to provide specialized functionality where needed
• declare template method to be fine (cannot be overidden by subclasses)
• the method implemented by subclasses is protected and abstract

Question 9

final classes

Answer 9

• cannot be inherited