从单个Java流中提取多个值

Question

我必须提取两个值（最小

public class MyClass {

    public static class MyC {
        double val;
        public MyC(double val) {
            this.val = val;
        }

        public double getVal() {return val;}
    }

    public static void main(String[] args) {


        List<MyC> list = new ArrayList<>();
        list.add(new MyC(10.0d));
        list.add(new MyC(20.0d));

        double min = Optional.ofNullable(list).stream()
                        .flatMap(List::stream)
                        .limit(13)
                        .map(MyC::getVal)
                        .min(Double::compare)
                        .orElse(getMinDefault());

        double max = Optional.ofNullable(list).stream()
                .flatMap(List::stream)
                .limit(13)
                .map(MyC::getVal)
                .max(Double::compare)
                .orElse(getMaxDefault());

    }

    private static double getMinDefault() {
        return 1.0d;
    }

    private static double getMaxDefault() {
        return 20.0d;
    }
}

Answer 1

您可以对value属性的最大值和最小值使用DoubleSummaryStatistics。

DoubleSummaryStatistics summaryStatistics = list // avoid initialising list as 'null'
        .stream()
        .limit(13)
        .mapToDouble(MyC::getVal)
        .summaryStatistics();
double max = summaryStatistics.getMax();
double min = summaryStatistics.getMin();

关于要依赖的自定义默认值，可以使用条件逻辑，例如：

double max = getMaxDefault();
double min = getMinDefault();
if (!list.isEmpty()) {
    DoubleSummaryStatistics summaryStatistics = list
            .stream()
            .limit(13)
            .mapToDouble(MyC::getVal)
            .summaryStatistics();

    max = summaryStatistics.getMax();
    min = summaryStatistics.getMin();
}