Helper decomposition

Q2 rewards helper decomposition — often explicitly ("a private helper may earn full credit if used correctly"). Two patterns:

The normalize helper. A class storing minutes could store raw seconds internally and normalize on write:

private int totalSeconds;
private void normalize() {
    minutes += seconds / 60;   // ...via fields
    seconds = seconds % 60;
}

The helper converts "carry" logic into one named place; mutators call it after every change. The exam rewards this when the spec says "invariant: seconds < 60 always".

The classify helper. Part (b) usually needs part (a)'s decision:

private boolean isPrime(int n) { ... }
public int countPrimes() {
    int c = 0;
    for (int v : values) { if (isPrime(v)) c++; }
    return c;
}

Writing the classifier as a helper makes (b) a two-liner and makes YOUR trace easier (test the helper on small inputs first).

Object interaction in Q2 — "the method takes another object of the same class": public void merge(Counter other) reads other's getters and mutates this. The trap: mutating other instead of this (aliased-parameter confusion), or reading this where other was meant. Name the target of every assignment out loud while writing.