Solution to the Inheritance Tutorial
------------------------------------

// A task to do.
public class Task {
    
    // The estimated amount of time needed to complete this task.
    protected int estimatedTime;

    // The actual amount of time needed to complete this task.
    protected int actualTime;
    
    // Constructs a new task with estimated time 'e'.
    public Task(int e) {
        estimatedTime = e;
        actualTime = 0;
    }

    // Completes this task with actual time 'a'.
    // Pre: a > 0.
    public void complete(int a) {
        actualTime = a;
    }

    // Returns true if this task is complete, false otherwise.
    public boolean isCompleted() {
        return actualTime > 0;
    }

    // Returns a description of this task.
    public String toString() {
        return
            "estimated time: " + estimatedTime + "; "
            "actual time: " + actualTime + "; "
            "isCompleted: " + isCompleted();
    }
}

// A task that involves studying.
public class StudyTask extends Task {

    // The subject to be studied.
    private String subject;

    // The books to study.
    private Vector books;

    // Constructs a new study task with estimated time 'e'
    // and subject 's'.
    public StudyTask(int e, String s) {
        super(e);
        subject = s;
        books = new Vector();
    }

    // Completes this task with actual time 'a'.
    // Pre: a > 0.
    public void complete(int a) {
        super.complete(a);

        // Throw away the books.
        books.clear();
    }

    // Adds book 'b' to the list of books to study.
    public void addBook(String b) {
        books.add(b);
    }

    // Returns a description of this task.
    public String toString() {
        return
            super.toString() + "; "
            "subject: " + subject + "; "
            "books: " + books;
    }
}