通过数组和流的转换来求平均值：

public class DoubleStream {
    public static void main(String[] args) {
        List<Double> doubleList = new ArrayList<>();
        doubleList.add(1.3);
        doubleList.add(2.2);
        doubleList.add(3.2);
        doubleList.add(4.3);
        doubleList.add(5.2);
        OptionalDouble average = Arrays.stream(doubleList.toArray(new Double[doubleList.size()])).mapToDouble(Number::doubleValue).average();
        System.out.println("平均值："+average);

    }
}