The Complete Data Set Workflow

Every data-driven program follows the same three phases:

1. Load: Read data from a file into an ArrayList of objects.
2. Store: Each row of data becomes one object; the ArrayList holds all objects.
3. Process: Apply algorithms (filter, count, aggregate, search) to answer questions.

// Phase 1 & 2: Load file into ArrayList of Student objects
ArrayList roster = new ArrayList();
try {
    File f = new File("students.txt");
    Scanner sc = new Scanner(f);
    while (sc.hasNext()) {
        String name = sc.next();
        int score = sc.nextInt();
        roster.add(new Student(name, score));
    }
    sc.close();
} catch (FileNotFoundException e) {
    System.out.println("File not found.");
}

// Phase 3: Process — count passing students
int passing = 0;
for (Student s : roster) {
    if (s.getScore() >= 70) passing++;
}
System.out.println("Passing: " + passing);

Applying Multiple Algorithms to One Data Set

Once loaded, the same ArrayList can be queried multiple ways without reloading:

// Average score
int total = 0;
for (Student s : roster) {
    total += s.getScore();
}
double avg = (double) total / roster.size();

// Highest scorer's name
Student best = roster.get(0);
for (int i = 1; i < roster.size(); i++) {
    if (roster.get(i).getScore() > best.getScore()) {
        best = roster.get(i);
    }
}
System.out.println("Top student: " + best.getName());

// All students above average
ArrayList aboveAvg = new ArrayList();
for (Student s : roster) {
    if (s.getScore() > avg) {
        aboveAvg.add(s);
    }
}

What the AP Exam Tests

FRQ #3 always follows this pattern:

• A class is given (like Student, Movie, Product) with a few instance variables and getter methods.
• An ArrayList of that class is given as a parameter.
• You write 1–2 methods that process the ArrayList using the algorithms you've practiced.

The file-reading code is typically given to you — you're tested on what you do with the data after it's loaded, not on the file-reading syntax itself.

Summary

• The complete workflow: file → Scanner → objects → ArrayList → algorithms.
• Load once, query many times — the ArrayList persists in memory for all processing.
• FRQ #3 gives you the class and ArrayList; you write the algorithm methods.
• Every algorithm from Lessons 4.5 and 4.10 applies to a loaded data set.

int count = 0;
for (Movie m : films) {
    if (m.getYear() > 8.0) count++;
}
return count;

return films.size();

int count = 0;
for (Movie m : films) {
    if (m.getRating() > 8.0) count++;
}
return count;

int count = 0;
for (Movie m : films) {
    if (m.getRating() >= 8.0) count++;
}
return count;

int total = 0;
for (WeatherReading r : readings) {
    total += r.getLow();
}
return (double) total / readings.size();

int total = 0;
for (WeatherReading r : readings) {
    total += r.getHigh();
}
return total / readings.size();

int total = 0;
for (WeatherReading r : readings) {
    total += r.getHigh();
}
return (double) total / readings.size();

int total = 0;
for (WeatherReading r : readings) {
    total += r.getHigh() + r.getLow();
}
return (double) total / readings.size();

for (WeatherReading r : readings) {
    if (r.getHigh() > 90) readings.remove(r);
}
return readings;

ArrayList hot = new ArrayList();
for (WeatherReading r : readings) {
    if (r.getHigh() > 90) hot.add(r);
}
return hot;

ArrayList hot = new ArrayList();
for (WeatherReading r : readings) {
    if (r.getLow() > 90) hot.add(r);
}
return hot;

ArrayList hot = new ArrayList();
for (WeatherReading r : readings) {
    if (r.getHigh() > 90) hot.add(r.getHigh());
}
return hot;

double total = 0;
for (Transaction t : ledger) {
    if (t.getCategory() == "Food") {
        total += t.getAmount();
    }
}
return total;

double total = 0;
for (Transaction t : ledger) {
    if (t.getAmount() == "Food") {
        total += t.getAmount();
    }
}
return total;

double total = 0;
for (Transaction t : ledger) {
    if (t.getCategory().equals("food")) {
        total += t.getAmount();
    }
}
return total;

double total = 0;
for (Transaction t : ledger) {
    if (t.getCategory().equals("Food")) {
        total += t.getAmount();
    }
}
return total;