Java 2 Object Orientation, Overloading & Overriding, Constructors & Return Types

Front 1

What is a key benefit of encapsulation?

Back 1

the ability to make changes in your implementation details behind a "public" programming interface

Front 2

What is your code's API?

Back 2

the set of accessible methods your code makes available for other code to call

Front 3

How do you make your design include encapsulation?

Back 3

1. Keep your instance varables protected (with an access modifier, often "private")
2. Make "public" accessor methods, and force calling code to use those methods
3. For the methods, use the JavaBeans naming conventions of set and get

Front 4

What do you call the methods that others must go through to access your instance variables?

Back 4

getters and setters
or
accessors and mutators

Front 5

You express the IS-A relationship in Java through the keyword _____.

Back 5

extends

Front 6

Wher does a class' arrow point towards in an inheritance tree?

Back 6

towards the class it extends

Front 7

What does it mean to say class A HAS-A B?

Back 7

if code in class A has a reference to an instance of class B.

Front 8

_____ can be overloaded or overridden but ______ can be only overloaded.

Back 8

Methods
constructors

Front 9

What do overloaded methods and constructors let you do?

Back 9

Use the same method name (or constructor) but with different argument lists.

Front 10

What does overriding let you do?

Back 10

redefine a method in a subclass, when you need a new subclass-specific behavior

Front 11

What kind of method can you not override?

Back 11

a final method

Front 12

What kind of methods are you forced to override?

Back 12

abstract methods

Front 13

What does the compiler look at, reference type or instance type?

Back 13

reference type

Front 14

______ lets you use a more abstract supertype (including an interface) reference to refer to one of its subtypes (including interface implementers)

Back 14

polymorphism

Front 15

Can an overriding method have a more restrictive access modifier than the method overridden?

Back 15

No

Front 16

Give the 8 rules for overriding a method.

Back 16

1. The argument list must exactly match that of the overridden method
2. The return type must exactly match that of the overridden method
3. The access level must no be more restrictive than that of the overridden method
4. The access level can be less restrictive than that of the overridden method
5. The overriding method must not throw new or broader checked exceptions
6. The overriding method can throw narrower or fewer exceptions
7. You cannot override a method marked final.
8. If a method can't be inherited, you cannot override it

Front 17

How can you take advantage of some of the code in the superclass version of a method, yet still override it to provide some additional specific behavior?

Back 17

Run the superclass version of the method, then come back and finish with subclass additional method code.

Front 18

What do overloaded methods let you do?

Back 18

lets you reuse the same method name in a class, but with different arguments (and optionally a different return type)

Front 19

What are the 5 rules for overloaded methods?

Back 19

1. Must change the argument list
2. Can change the return type
3. Can change the access modifier
4. Can declare new or broader checked exceptions
5. A method can be overloaded in the same class or in a subclass

Front 20

Which overridden method to call is decided at ______ based on object type, but which overloaded version of the method to call is based on the reference type at ____ time.

Back 20

runtime
compile

Front 21

Is the choice of which overloaded method to call dynamically decided at runtime?

Back 21

No, it is based on the reference type passed at compile time

Front 22

Can a method be both overloaded and overridden?

Back 22

Yes

Front 23

You cannot make a new object without invoking _________.

Back 23

its constructor and the constructor of each of its superclasses

Front 24

Does every class, including abstract classes, have to have a constructor?

Back 24

Yes

Front 25

A constructor has no _____ and its name must exactly match ____.

Back 25

return type
the class name

Front 26

What is the typical use of constructors?

Back 26

to initialize instance variables

Front 27

Can constructors use any modifier?

Back 27

Yes, including private

Front 28

Is it legal to have a method with the same name as the class but it isn't a constructor?

Back 28

Yes - but stupid
Note: if you see a return type, it's a method rather than a constructor

Front 29

What happens if you don't type a constructor into your class code?

Back 29

A default constructor will be automatically generated by the compiler.

Front 30

What is true about the default constructor?

Back 30

It is always a no-arg constructor

Front 31

If you type a constructor with arguments, will you also have a no-arg constructor?

Back 31

No - not unless you type it in yourself

Front 32

What must be the first statement of a constructor be?

Back 32

A call to an overloaded constructor (this()) or a call to the superclass constructo (super()).

Front 33

What if you type in a constructor and you do not type in the call to super()?

Back 33

the compiler will insert a no-arg cal to super() for you

Front 34

If you type in your own no-arg constructor, will it be the default constructor?

Back 34

No - the default constructor is the one the compiler provides

Front 35

Can you call an instance method or access an instance variable before the super constructor runs?

Back 35

No

Front 36

What are the only types of variables and methods that can be accessed as part of the call to "super()" or "this()"?

Back 36

only static variables and methods

Front 37

Do abstract classes have constructors?

Back 37

Yes - they are always called when a concrete class is instantiated

Front 38

Do interfaces have constructors?

Back 38

No - they are not part of an object's inheritance tree

Front 39

What is the only way a constructor can be invoked?

Back 39

from within another constructor

Front 40

How does the default constructor look?

Back 40

1. it as the same access modifier as the class
2. it has no arguments
3. it includes a no-arg call to the super constructor

Front 41

What must you do if your superclass does not have a no-arg constructor?

Back 41

You must type a constructor in your class (the subclass) because you need a place to put in the call to super with the appropriate arguments

Front 42

Can constructors be overridden?
Can constructors be overloaded?

Back 42

No - because they are not methods
Yes

Front 43

What does it mean to overload a constructor?

Back 43

Typing in multiple versions of the constructor each having a different argument list.

Front 44

How are overloaded constructors used?

Back 44

To provide alternate ways for clients to instantiate objects of your class

Front 45

The first line in a constructor must be a call to ______ or a call to ______.

Back 45

"super()"
"this()"

Front 46

Can a constructor have both a call to "super()" and a call to "this()"?

Back 46

No, because each of these must be the very first statement in a constructor

Front 47

What is the benefit of having one constructor invoke another constructor?

Back 47

to avoid code duplication

Front 48

Can you change the return type for an overloaded method?

Back 48

Yes - because an overloaded method is a completely different method from any other method with the same name - of course you must change the argument list

Front 49

Can overriding methods change the return type?

Back 49

No - they must match the inherited version exactly

Front 50

Can you return "null" in a method that has an object reference return type?

Back 50

Yes

Front 51

Is an array a legal return type?

Back 51

Yes

Front 52

In a method with a primitive return type what can you return?

Back 52

any value or variable that can be implicitly converted to the declared return type

Front 53

In a method with a primitive return type can you return a value or variable that can be explicitly cast to the declared return type?

Back 53

Yes

Front 54

Can you return anything from a method with a "void" return type?

Back 54

No

Front 55

In a method with an object reference return type, what can you return?

Back 55

any object type that can be implicitly cast to the declared return type

Front 56

What kind of object can be returned from methods that declare an abstract class or interface return type?

Back 56

an object that passes the IS-A test can be returned