java8 list统计（求和、最大、最小、平均）详解编程语言

list.stream().mapToDouble(User::getHeight).sum()//和 
list.stream().mapToDouble(User::getHeight).max()//最大 
list.stream().mapToDouble(User::getHeight).min()//最小 
list.stream().mapToDouble(User::getHeight).average()//平均值

public class HelloWorld { 
    private static final DecimalFormat df = new DecimalFormat("0.00");//保留两位小数点 
    public static void main(String[] args) { 
        Random random = new Random(); 
        List<User> list = new ArrayList<>(); 
        for(int i=1;i<=5;i++) { 
            double weight = random.nextDouble() * 100 + 100;//随机身高：100-200 
            User u = new User(i, "用户-" + i, weight); 
            list.add(u); 
        } 
        System.out.println("用户：" + list); 
        double sum = list.stream().mapToDouble(User::getHeight).sum(); 
        System.out.println("身高 总和：" + df.format(sum)); 
        double max = list.stream().mapToDouble(User::getHeight).max().getAsDouble(); 
        System.out.println("身高 最大：" + df.format(max)); 
        double min = list.stream().mapToDouble(User::getHeight).min().getAsDouble(); 
        System.out.println("身高 最小：" + df.format(min)); 
        double average = list.stream().mapToDouble(User::getHeight).average().getAsDouble(); 
        System.out.println("身高 平均：" + df.format(average)); 
 
    } 
    private static class User{ 
        Integer id; 
        String name; 
        double height;//身高 
 
        public User(Integer id, String name, double height) { 
            this.id = id; 
            this.name = name; 
            this.height = height; 
        } 
 
        public Integer getId() { 
            return id; 
        } 
 
        public void setId(Integer id) { 
            this.id = id; 
        } 
 
        public String getName() { 
            return name; 
        } 
 
        public void setName(String name) { 
            this.name = name; 
        } 
 
        public double getHeight() { 
            return height; 
        } 
 
        public void setHeight(double height) { 
            this.height = height; 
        } 
 
        @Override 
        public String toString() { 
            return "User{" + 
                    "id=" + id + 
                    ", name='" + name + '/'' + 
                    ", height=" + height + 
                    '}'; 
        } 
    } 
 
}

用户：
    [User{id=1, name='用户-1', height=192.15677342306662}, 
     User{id=2, name='用户-2', height=196.35056058694772}, 
     User{id=3, name='用户-3', height=101.96271958293853}, 
     User{id=4, name='用户-4', height=110.83134063008366}, 
     User{id=5, name='用户-5', height=106.27720636757154}] 
身高 总和：707.58 
身高 最大：196.35 
身高 最小：101.96 
身高 平均：141.52

public class HelloWorld { 
    private static final DecimalFormat df = new DecimalFormat("0.00");//保留两位小数点 
    public static void main(String[] args) { 
        Random random = new Random(); 
        List<User> list = new ArrayList<>(); 
        for(int i=1;i<=5;i++) { 
            double weight = random.nextDouble() * 100 + 100;//随机身高：100-200 
            list.add(new User(i, new BigDecimal(weight).setScale(BigDecimal.ROUND_HALF_UP, 2))); 
        } 
        System.out.println("list：" + list); 
        BigDecimal add = list.stream().map(User::getHeight).reduce(BigDecimal.ZERO, BigDecimal::add); 
        System.out.println("身高 总和：" + df.format(add)); 
        Optional<User> max = list.stream().max((u1, u2) -> u1.getHeight().compareTo(u2.getHeight())); 
        System.out.println("身高 最大：" + df.format(max.get().getHeight())); 
        Optional<User> min = list.stream().min((u1, u2) -> u1.getHeight().compareTo(u2.getHeight())); 
        System.out.println("身高 最小：" + df.format(min.get().getHeight())); 
 
    } 
    private static class User{ 
        Integer id; 
        BigDecimal height;//身高 
 
        public User(Integer id, BigDecimal height) { 
            this.id = id; 
            this.height = height; 
        } 
 
        public Integer getId() { 
            return id; 
        } 
 
        public void setId(Integer id) { 
            this.id = id; 
        } 
 
        public BigDecimal getHeight() { 
            return height; 
        } 
 
        public void setHeight(BigDecimal height) { 
            this.height = height; 
        } 
 
        @Override 
        public String toString() { 
            return "User{" + 
                    "id=" + id + 
                    ", height=" + height + 
                    '}'; 
        } 
    } 
 
}

list：
    [User{id=1, height=141.5472}, 
　　　　User{id=2, height=133.1609}, 
　　　　User{id=3, height=101.5403}, 
　　　　User{id=4, height=157.8470}, 
　　　　User{id=5, height=177.7596}] 
身高 总和：711.8550 
身高 最大：177.76 
身高 最小：101.54