ECM2414 Nested Loops

Question 1

OOP benefits

Answer 1

• Protected private and public variables in created objects (Encapsulation)
• (Inheritance)
• Organises code into classes and objects
• (Polymorphism)

Question 2

Issue with encapsulation

Answer 2

• Classes in OOP should usually be specialised, should only include code relating to that type’s specific function
• With two tightly coupled classes
  ○ Rely heavily on the members in each class
  ○ Lots of work involved in creating functions to access those members
  ○ Occurs more frequently in GUI programming

Nested classes overcome this issue by allowing classes to be defined within classes

Question 3

Static nested class

Answer 3

does not have access to instance members

Question 4

inner class

Answer 4

does not have access to instance members

Question 5

Instance members

Answer 5

refers to variables that are specific to that specific object

Question 6

What modifiers can be used to declare a standard outer class (top-level class)

Answer 6

public

package private (the default/implicit)

Question 7

modifiers for nested classes

Answer 7

public
private
protected
package private

Question 8

protected modifier

Answer 8

an access modifier that limits the visibility of functions and variables to a specific class and its derived classes

Question 9

package private

Answer 9

other members of the same package have access to the item. package-private is the default access modifier and does not have a keyword, because package is used to specify the package for a class or interface.

Question 10

Why use nested classes

Answer 10

Loosely linked classes located in one place
- Links can be made explicit between classes that are linked to only one other class by making it a nested class

Increases encapsulation on occasion (hiding data for private purposes, you are not able to take access of every data at any time in your code, which is safe)

It makes code more readable (classes pertaining to a top level class are all found under that top level class, looking stately)

Question 11

Nested classes will produce two class files on compilation

Take the example of a top-level class OuterClass and its nested class InnerClass. What would the class files be named?

Answer 11

OuterClass.class
OuterClass$InnerClass.class

Question 12

How can static nested classes be accessed?

Answer 12

using the enclosing class name
e.g. OuterClass.InnerClass

from within the class however, you can construct the nested class directly with just ‘InnerClass’

Question 13

“this”

Answer 13

refers to the inner type instance

OuterClass.this refers to the instance of the surrounding (outer) class, when within the inner class code blocks

In a similar vain to how regular public variables are accessed within a class, not just nested classes

Question 14

Local classes

Answer 14

Local classes are defined and exist solely within a block (usually a method)

Local class declaration cannot contain public, protected, private or static access modifiers

Cannot access method local variables (unless passed as arguments) unless they are declared as final

Can access all the members of the outer class instance like standard inner class members

External access to the class cannot be made

explicit finals initialised outside the class within the block can be accessed

Question 15

Anonymous classes

Answer 15

Potentially one of the most convoluted aspects of java

Classes that are declared without any class name at all (hence the name anonymous)

Not only may these be defined within a method, they may also be defined within an argument to a method

Uses the ‘new’ keyword, then uses curly bracers to extend the base implementation

When you implement an interface, there is no constructor, so you use an empty pair of parentheses

Question 16

Why not use a 0-6 of a byt instead of enum class?

Answer 16

Because:
- Must map between the byte value and the day
- Must check for range errors