Software Access Modifiers

Question 1

What are the two access modifier levels?

Answer 1

• Top level (class level) – can use public
  
  • Member level (inside class) – can use public, private, protected

Question 2

How do access levels affect programming?

Answer 2

1. When using classes that come from another source, access levels determine which members of those classes your own classes can use.
2. When writing a class, you need to decide what access level every member variable and every method in you class should have.

Question 3

Why use access modifiers?

Answer 3

By making class members private or public, the class interface is clearly separated from the internal implementation of the class. This is called encapsulation. From a security viewpoint, encapsulation stops class members from being changed in an uncontrolled way (e.g. without proper validation, without notifying error handlers, etc).

Question 4

How to choose access modifiers?

Answer 4

Use the most restrictive access level that makes sense for a particular class member. Use private unless you have a good reason not to. Avoid public fields except for constants which cannot be changed.

Public fields tend to:
- Restrict the code to a particular implementation.
- Limit flexibility in changing the code

Question 5

What are immutable objects?

Answer 5

An immutable object is an object whose internal state remains constant after it has been created.