mode 2

Question 1

What is a constructor?

Answer 1

A constructor is a special type of method that is used to initialize an object during its construction.

A constructor has the same name as the class and DOESN’T have a return type.

Question 2

Types of constructors

Answer 2

default constructor

No args constructor: implicit derived constructor when none given.

args constructor

Question 3

What is an initialization block?

Answer 3

An initializer block is basically a method without a name, so when java sees the block it will call the block IMMEDIATELY because it knows that you won’t ever be able to refer to the block again.

The initializer block will be called every time a class is instantiated

Question 4

What is static initializer block

Answer 4

The static initializer block is a type of initializer block that will run ONCE the FIRST time anyone calls its class for anything

It will NOT run for EVERY instance created

Question 5

What is scope in Java?

Answer 5

The area where a variable exists. Outside of this area the variable does not exist.

This is NOT to be confused with access levels…that happen to determine who has access to a variable when it DOES exist.

It deals with permissions, not existence.

Question 6

What are the scopes in java?

Answer 6

• -class scope (aka static scope)
  
  • -object scope (aka instance scope)
  • -method scope
  • -block scope

Question 7

What is the order of effect in our program?

Answer 7

Order of “effect”:

1. static variables/methods (runs ONCE the first time the class is needed)
2. static initializer blocks (runs ONCE the first time the class is needed)
3. instance variables (runs EVERY TIME an instance of this class is created)
4. instance initializer blocks (runs EVERY TIME an instance of this class is created)
5. constructors

Question 8

Where can the static keyword be used?

Answer 8

The static keyword can be used on:

• variables
• methods
• classes (only inner classes)
• interfaces (only inner interfaces)
• initializer blocks

It can’t be used on constructors though.

Question 9

Can we make a static variable inside a static method?

Answer 9

No!

Question 10

Inheritance: What is an “is a” relationship vs a “has a” relationship?

Answer 10

-“is a” means you ARE a type of the specific object;
it’s like living a double life, where you have two identities

-“has a” means you CONTAIN a type of the specific class;
it’s like owning a car…you are NOT a car…you just own one

Question 11

What is the inheritance heirachy

Answer 11

Our Hierarchy

• Object
• |
• Animal
• / \
• Monkey Turtle
• / \
• Chimp ChimpSibling

Question 12

Name a few types of polymorphism

Answer 12

There are many types of polymorphism

	 * -overriding
	 * -overloading is compile time polymorphism
	 * -upcasting is polymorphism
	 * -downcasting is polymorphism

Question 13

What is upcasting & downcasting in java

Answer 13

Upcasting is the typecasting of a child object to a parent object

Implicit upcasting:
Animal myAniChimp = new Chimp();
Explicity upcasting:
Chimp myChimp = new Chimp();
Animal myAnimalTwo = (Animal)myChimp;

Downcasting means the typecasting of a parent object to a child object
                Animal myAnimalFour = new Chimp();
		Chimp myChimpFour = (Chimp)myAnimalFour;

Question 14

what is overloading & overriding?

Answer 14

Overloading: a feature of Java in which a class has more than one method of the same name and their parameters are different

Overriding: A child class creating a method with the SAME NAME (and parameter list) as a method in the parent class; this results in the behavior/functionality being altered

Question 15

Why is upcasting and downcasting useful?

Answer 15

It helps us achieve modularity.

It enables us to decouple our code

Question 16

What is tightly coupled code & decoupling ?

Answer 16

Tightly coupled code or spaghetti code is code that is written in such a way where small changes to one file creates a wave of changes many other source code files.

Question 17

Can we override a method in Java? a variable in Java?

Answer 17

Yes we can override a method.

No we can’t override a variable.

Question 18

What is shadowing

Answer 18

In java when a child class has a variable with the same name as a variable in the parent class….then we SHADOW the parent’s variable.

This is a concept called shadowing; not overriding

Question 19

CAN I override a STATIC method?

CAN I override an initializer block?

CAN I override a constructor?

Answer 19

No, we can’t override a static method, but we can shadow it.

No, we can’t override an initializer block? it doesn’t make sense to

No, we can’t override a constructor? it doesn’t make sense to

Question 20

What is the first line of the constuctor?

Answer 20

The super() keyword. It is implicitly written but can be explicitly written out too.

Question 21

What does the super() keyword do?

Answer 21

It calls to the direct parent constructor and gives access to parent constructor, methods, fields.

Question 22

Can we use super() to access a parent class members from outside of the object?

Answer 22

No we can’t. In order to access parent class members from outside of the object, we use upcasting.

To access from inside a class, we use super();

Question 23

Does Java support multiple inheritance?

Answer 23

No, this is because the child can only point to one parent in the constructor.

Question 24

this vs super. what is the difference?

Answer 24

“this” is a reference to the current object we’re currently inside of(specifically to its instance & static members)

“super” is a reference to the current objects direct parent class.

both this and super can’t exist at the same time

with BOTH the “this” and “super” keywords we can access fields(aka state variable), methods, and constructors

Question 25

What is the override and deprecated notation

Answer 25

The override annotation is for clarity/readability AND it ensures that there IS a method in the parent class that you are overriding (it protects you from misspelling the method name)

The deprecated annotation lets the developers know that this functionality will no longer be supported in the future. IT STILL DOES FUNCTION, but the developer should move to a new functionality that is designed to replace the existing deprecated functionality.

Question 26

difference between this()/super() and this./super.

Answer 26

for this()/super() we make call to constructor

for this./super. we make call to only the members