Grid search and the null contract

Searching a grid — find a value and report where it lives:

// returns {row, col} or null if absent
public static int[] find(int[][] g, int target) {
    for (int r = 0; r < g.length; r++) {
        for (int c = 0; c < g[0].length; c++) {
            if (g[r][c] == target) {
                return new int[] {r, c};
            }
        }
    }
    return null;
}

Three habits from this snippet that recur on FRQ 4:

• Early return the moment the target is found — no flag needed.
• Return null (or a sentinel like -1) when not found; the contract must say which. null means "no object here" — calling a method on it throws NullPointerException.
• Test the not-found path on purpose. Un-tested contracts rot.

Grid size conventions: many AP grids are square-ish or have different row/column counts on purpose — {{1,2,3},{4,5}} is legal (a "ragged" shape, though the exam's grids are usually rectangular). Never assume rows and columns are interchangeable: g[r][c] and g[c][r] are different cells, and one of them may not exist.