Section 8.1 Worked Example: Writing Classes - Attributes
Subsection 8.1.1 Subgoals for Writing a Class 1/4
Name it
Differentiate class-level (static) vs. instance/object-level variables
Differentiate class-level (static) vs. instance/object behaviors/methods
-
Define class variables (static) as needed ‘
Name
Data Type
public / private / final
-
Define instance variables (that you want to be interrelated)
Name
Data Type
private
You can watch this video or read through the content below it.
Problem: We will be writing a class to represent an instance of time, like a specific time in the day.
For the first part, determine the appropriate attributes (data) to be stored and declare them
Subsection 8.1.2 SG1: Name it
We will call the class TimeType
Subsection 8.1.3 SG2: Differentiate class-level (static) vs. instance/object-level variables
class-level (static) data: one value shared between ALL instances instance-level data: each instance has its own copy
For time, we want all time instances to be in the same format so static data for format, everything else instance
Subsection 8.1.4 SG3: Differentiate class-level (static) vs. instance/object behaviors/methods
All methods will be instance level as the format will be fixed an unchangeable
Subsection 8.1.5 SG4: Define class variables (static) as needed
public class TimeType {
public static final boolean FORMAT24 = true;
}
Note the use of the final keyword to define FORMAT24 as a constant, which makes it safe to expose as public. An alternate implementation might choose to make this value mutable, but private, using static methods to ssssssssaccess and alter it.
Subsection 8.1.6 SG5: Define instance variables (that you want to be interrelated)
public class TimeType {
//static var
public static final boolean FORMAT24 = true;
//instance vars
private int hour;
private int minute;
private int second;
}
