Section 8.3 Worked Example: Writing Classes - Constructors
Subsection 8.3.1 Subgoals for Writing a Class 2/4
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
-
Create constructor (behavior) that creates initial state of object
public
Same name as class
No return type
Default - no parameters
Logic - initialize all variables
Repeat as needed, adding parameters
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.
The attributes have been declared, now write a default and overloaded constructor.
Subsection 8.3.2 SG6: Create constructor (behavior) that creates initial state of object
6A, 6B, & 6C: All constructors are public, with no return type, and named the same as the class.
6D: We will start with the default constructor, which has no parameters.
All together, the default constructor has a header/signature of:
public TimeType() {
}
6E. Logic - initialize all variables
public TimeType () {
hour = 0;
minute = 0;
second = 0;
}
6F. Repeat as needed, adding parameters
public TimeType (int hr, int min, int sec) {
if (hr >=0 && hr <= 23)
hour = hr;
if (min >= 0 && min <= 59)
minute = min;
if (sec >= 0 && sec <= 59)
second = sec;
}
We are now able to construct TimeType objects from the main method in two ways
public static void main (String [] args) {
TimeType midnight = new TimeType(); //call the default constructor
TimeType noon = new TimeType(12, 0, 0); //call an overloaded constructor
}
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