AP Computer Science tutor in Germany

Source: College Board, AP Central, AP Computer Science A Exam and AP Computer Science Principles Exam pages, read 3 November 2026. We are not connected with the College Board.

Our task, in the CSA style. A class PracticeLog stores the minutes four pupils practised on each school day, one row per pupil and one column per weekday. Write totalForDay, which adds up one column; busiestDay, which returns the index of the day with the largest total; and everyDayCount, which counts the pupils who practised on all five days.

public class PracticeLog {
    private int[][] minutes;

    public PracticeLog(int[][] minutes) {
        this.minutes = minutes;
    }

    public int totalForDay(int day) {
        int total = 0;
        for (int row = 0; row < minutes.length; row++) {
            total += minutes[row][day];
        }
        return total;
    }

    public int busiestDay() {
        int top = 0;
        for (int day = 1; day < minutes[0].length; day++) {
            if (totalForDay(day) > totalForDay(top)) {
                top = day;
            }
        }
        return top;
    }

    public int everyDayCount() {
        int count = 0;
        for (int[] pupil : minutes) {
            boolean allDays = true;
            for (int m : pupil) {
                if (m == 0) {
                    allDays = false;
                }
            }
            if (allDays) {
                count++;
            }
        }
        return count;
    }

    public static void main(String[] args) {
        String[] days = {"Mon", "Tue", "Wed", "Thu", "Fri"};
        int[][] data = {
            {30, 0, 45, 20, 0},
            {25, 30, 30, 25, 40},
            {0, 50, 60, 0, 15},
            {20, 20, 35, 30, 10}
        };
        PracticeLog log = new PracticeLog(data);
        System.out.println("Wednesday total: " + log.totalForDay(2));
        System.out.println("Busiest day: " + days[log.busiestDay()]);
        System.out.println("Practised every day: " + log.everyDayCount());
    }
}

Look at the two loops. totalForDay keeps the column fixed and moves down the rows, so the outer index is the row and the limit is minutes.length. everyDayCount goes the other way, one whole pupil at a time, with enhanced for loops. We tried both classic slips. Give busiestDay the limit minutes.length and, on this four by five grid, it would quietly skip Friday: it still compiles and still prints Busiest day: Wed, so the bug hides until Friday is the busiest day. Give totalForDay the limit minutes[0].length instead and Java stops with ArrayIndexOutOfBoundsException: Index 4 out of bounds for length 4. The loud bug is the kind one; a hand trace is what catches the quiet one. Note also that busiestDay keeps the first day when two totals tie, because it only moves on a strictly larger total: Monday and Thursday both have 75, and a question may ask you which one should win.

1. Trace it. Before running anything, write down the value of total after each pass of the loop in totalForDay(2).
2. Expose the quiet bug. Change one number in the data so that Friday becomes the busiest day, then run the version of busiestDay with the wrong limit and watch it give the wrong answer.
3. Extend it. Add quietestPupil, returning the row with the smallest sum, and decide what it should do on a tie.

Source: College Board, AP Computer Science Principles Exam page (Section II, written response prompt categories), read 3 November 2026.

Under-18 pupils in our classes do not use AI tools whose providers set an adult minimum age; the AI tools age guide quotes each provider's terms. That matters twice over for CSP, where the College Board also addresses AI use in the Create task.

AGIS, the body that represents international schools in Germany, keeps an online directory; in it, Advanced Placement appears for Black Forest Academy, together with a US curriculum and diploma; at Frankfurt International School, alongside the IB; and at John F. Kennedy School Berlin, alongside an American high school diploma and the Deutsches Abitur. We name these schools only as context from AGIS: we are not connected with them or with AGIS, and they are not a source of our students.

Pupils in Germany usually come to us for one of three reasons: the school offers one AP Computer Science course but not the other, the pupil wants to sit the exam a year early and needs to cover the course faster, or Java is new and the class moves too fast. In each case we teach alongside the school. The AP coordinator orders exams and the College Board sets and scores them; we do not.

German legal time follows the Einheitenzeitgesetz: UTC+1 (MEZ) in winter and UTC+2 (MESZ) in summer, with summer time ending on 25 October 2026 and starting again on 28 March 2027. India uses UTC+5:30 the whole year. The rows are examples, not fixed groups.

When you book the free first class, you choose its time in your own clock. In April and early May 2027, one-to-one pupils often move to three short sessions a week for timed practice.