Java 2 Inner Classes

Front 1

Describe the "special relationship" that an inner class instance shares with an instance of the outer class.

Back 1

It gives code in the inner class access to members of the enclosing (outer) class - even those marked private, as if the inner class were part of the outer class (or really a full-fledged member of the outer class).

Front 2

When we say "regular" inner class , what is it not?

Back 2

it is not
1. static
2. method-local
3. anonymous

Front 3

What is the only way you can access a regular inner class?

Back 3

Through a live instance of the outer class

Front 4

To instantiate an instance of a regular inner class, what must you have?

Back 4

An instance of the outer class to tie to the inner class.

Front 5

Why can't you instantiate a regular inner class from a "static" method of the outer class?

Back 5

Because in static code, there is no "this" reference

Front 6

If you have an outer class MyOuter with a regular inner class MyInner, what two class files do you get when you do:
%javac MyOuter.java

Back 6

MyOuter.class
MyOuter$MyInner.class

Note: the inner class file isn't accessible to you in the usual way.

Front 7

What code would you use in a main method outside the outer class MyOuter to make an instance of the regular inner class MyInner?

Back 7

either:

MyOuter mo = new MyOuter();
MyOuter.MyInnner inner = mo.new MyInner();

or:

MyOuter.MyInner inner = new MyOuter().new MyInner();

Front 8

How does an object refer to itself normally?

Back 8

Using the "this" reference.

Front 9

To reference the regular inner class instance itself, from within the inner class code, use _____.

Back 9

this

Front 10

To reference the "outer this" (the outer class instance) from within the regular inner class code, use _____.

Back 10

.this (example, MyOuter.this)

Front 11

A regular inner class is a member of the outer class so what modifiers can be applied to it?

Back 11

final, abstract, public, private, protected, static (except this turns it into a static nested class rather than a regular inner class), strictfp

Front 12

A regular inner class is scoped where?

Back 12

inside another class' curly braces, but outside any method code.

Front 13

What is a method-local inner class?

Back 13

An inner class defined within a method.

Front 14

What is the only place that a method-local inner class can be instantiated?

Back 14

Only within the method where the inner class is defined and it must be below the inner class definition.

Front 15

Can a method-local inner class use the local variables of the method the inner class is in? Why or Why not?

Back 15

No, unless the local variables are marked final. Because local variables live on the stack so aren't guaranteed to be alive as long as the method-local inner class object which lives on the heap.

Front 16

What happens if you try to access a local variable within a method-local inner class?

Back 16

The compiler gets upset - it won't compile (unless it is final).

Front 17

What are the only modifiers you can apply to a method-local inner class?

Back 17

abstract and final (but, of course, never both at the same time).

Front 18

If you're in a static method, there is no ____, so an inner class in a static method is subject to the same restrictions as the static method. In other words, no access to _____.

Back 18

"this"
"instance variables"

Front 19

A local calls declared in a static method has access to only ____ members of the enclosing class, since there is no associated _____ of the enclosing class.

Back 19

"static"
"instance"

Front 20

What is the whole point of making an anonymous inner class?

Back 20

To override one or more methods of the superclass or to implement methods of an interface.

Front 21

What is the syntax for closing off an anonymous inner class definition?

Back 21

");" Notice especially the semicolon.

Front 22

Can you call a method in an anonymous inner class that is a new method (i.e. does not override a method in the superclass)?

Back 22

No - you get a compiler error.

Front 23

What are the two flavors of anonymous inner classes?

Back 23

1. creates an anonymous subclass of the specified class type.
2. creates an anonymous implementer of the specified interface type.

Front 24

How many interfaces can an anonymous inner class implement?

Back 24

one

Front 25

If you have an anonymous inner class defined right inside the argument, what is the syntax at the end of it?

Back 25

"});" end inner class def, arg, and end statement

Front 26

Does an instance of an static nested class enjoy a special relationship with an instance of the outer class?

Back 26

No

Front 27

What is a staic nested class?

Back 27

A class that's a static member of the enclosing class. It does not have access to the instance variables and methods of the outer class.
Note: static means it can be accessed without having an instance of the outer class.

Front 28

Give the syntax for instantiating a static nested class Nested with the outer class named BigOuter.

Back 28

BigOuter.Nested n = new BigOuter.Nested();

Front 29

Do you need an instance of the enclosing class to instantiate a static nested inner class?

Back 29

No - they do not share a special relationship with any instance of the enclosing class

Front 30

Why can't a static nested class access nonstatic members of the outer class?

Back 30

Because it does not have an implicit reference to any outer instance (it does not get an outer "this" reference).