5.1 Anatomy of a Class

• Class: blueprint used to create objects
• Instances, attributes, constructors, methods
• Objects: instances of a class
• public: no restricted access -- classes and constructors
• private: restrict access -- instance variables

5.2 Constructors

• initializes instance variables when an object is created
• Each object has attributes which are the instance of a class
• Constructors set the initial state of an object by assigning initial values to instance variables

5.3 Comments

• ignored by compiler
• make code more readable
• not required for the AP exam

5.4 Accessor Method

• Allows objects outside of the class to obtain values
• non void returns a single value
• toString() Method

5.5 Mutator Method

• Don't return values
• Must be used when different classes need to modify instance variables

2019 FRQ Question 2

public class StepTracker
{
    private int minSteps;
    private int totalSteps;
    private int numDays;
    private int numActiveDays;
    public StepTracker(int threshold)
    {
        minSteps = threshold;
        totalSteps = 0;
        numDays = 0;
        numActiveDays = 0;
    }
    public void addDailySteps(int steps)
    {
        totalSteps += steps;
        numDays++;
        if (steps >= minSteps)
        {
            numActiveDays++;
        }
    }
    public int activeDays()
    {
        return numActiveDays;
    }
    public double averageSteps()
    {
        if (numDays == 0)
        {
            return 0.0;
        }
        else
        {
            return (double) totalSteps / numDays;
        }
    }
}