MovingAverageV2.java

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.ArrayDeque;
import java.util.Queue;
import java.util.Random;

public class MovingAverageV2 {

    private final Queue<BigDecimal> window = new ArrayDeque<>();
    private final int period;
    private BigDecimal sum = BigDecimal.ZERO;

    public MovingAverageV2(int period) {
        this.period = period;
    }

    public void add(BigDecimal num) {
        sum = sum.add(num);
        window.add(num);
        
        if (window.size() > period) {
            sum = sum.subtract(window.remove());
        }
    }

    public BigDecimal getAverage() {
        if (window.isEmpty()) {
            return BigDecimal.ZERO;
        }
        
        BigDecimal divisor = BigDecimal.valueOf(window.size());
        return sum.divide(divisor, 2, RoundingMode.HALF_UP);
    }
    
    public static void main(final String[] args) {
        final Random random = new Random();
        
        warmup(random);
        
        final MovingAverage ma = new MovingAverage(10);
        final MovingAverageV2 mav2 = new MovingAverageV2(10);
        
        long startTime = System.nanoTime();
        
        for (int i = 0; i < 10_000_000; ++i) {
            ma.add(BigDecimal.valueOf(random.nextLong()));
        }
        
        long endTime = System.nanoTime();
        
        System.out.printf("MovingAverage in   %.1f milliseconds.\n",
                          (endTime - startTime) / 1e6);
        
        startTime = System.nanoTime();
        
        for (int i = 0; i < 10_000_000; ++i) {
            mav2.add(BigDecimal.valueOf(random.nextLong()));
        }
        
        endTime = System.nanoTime();
        
        System.out.printf("MovingAverageV2 in %.1f milliseconds.\n",
                          (endTime - startTime) / 1e6);
    }
    
    private static void warmup(final Random random) {
        final MovingAverage ma = new MovingAverage(10);
        final MovingAverageV2 mav2 = new MovingAverageV2(10);
        
        for (int i = 0; i < 100; ++i) {
            for (int j = 0; j < 10_000; ++j) {
                final BigDecimal value = BigDecimal.valueOf(random.nextLong());
                ma.add(value);
                mav2.add(value);
            }
        }
    }
}