Complete Class Design

A complete class follows a standard order: private instance variables, constructors, accessors, mutators, and behavior methods. Following this template makes your code easy to read and matches what AP graders expect.

The pieces work together: the constructor initializes the fields; accessors expose them; mutators change them safely; behavior methods do useful work using the state.

On the AP exam, class design FRQs ask you to write all these pieces from a written specification.

Complete Book class

public class Book {
    // 1. Instance variables
    private String title;
    private String author;
    private int pagesRead;
    private int totalPages;

    // 2. Constructor
    public Book(String title, String author, int totalPages) {
        this.title = title;
        this.author = author;
        this.totalPages = totalPages;
        this.pagesRead = 0;
    }

    // 3. Accessors
    public String getTitle() { return title; }
    public String getAuthor() { return author; }
    public int getPagesRead() { return pagesRead; }
    public int getTotalPages() { return totalPages; }

    // 4. Mutator
    public void readPages(int n) {
        pagesRead = pagesRead + n;
        if (pagesRead > totalPages) pagesRead = totalPages;
    }

    // 5. Behavior
    public boolean isFinished() {
        return pagesRead == totalPages;
    }

    public double percentComplete() {
        return 100.0 * pagesRead / totalPages;
    }
}

Constructor initializes everything

Every field gets a starting value — either from a parameter or a sensible default like 0 or null.