Writing Classes in AP CSA

FRQ #2 on every AP CSA exam asks you to write a complete class from scratch. This is one of the most predictable point sources on the exam — master the anatomy of a class and you’re guaranteed partial credit at minimum.

Anatomy of a Class

public class Dog {
    // 1. Private instance variables
    private String name;
    private int age;

    // 2. Constructor
    public Dog(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // 3. Accessor (getter)
    public String getName() {
        return name;
    }

    // 4. Mutator (setter)
    public void setAge(int newAge) {
        age = newAge;
    }

    // 5. Other methods
    public String toString() {
        return name + " is " + age + " years old";
    }
}

The this Keyword

When a parameter name matches an instance variable name, use this to distinguish them:

public Dog(String name, int age) {
    this.name = name;  // this.name = instance variable
    this.age = age;    // age alone = parameter
}

public class Car {
    String model;
        public Car(String m) {
        model = m;
    }
        public String getModel() {
        return model;
    }
}