Moving average for performance measurements in Java

MovingAvg.java

public class MovingAvg {
    public final long[] measurements;
    public final int size;
    private int pointer = 0;

    public MovingAvg(int size) {
        measurements = new long[size];
        this.size = size;
    }

    public void add(long time) {
        measurements[pointer++ % size] = time;
    }

    public int count() {
        return Math.min(pointer, size);
    }

    public double avg() {
        if (pointer == 0)
            throw new RuntimeException("no measurements");

        double sum = 0;
        int count = count();
        for (int i = 0; i < count; ++i)
            sum += measurements[i];
        return sum / count;
    }
}