Java8 List统计（最大值，最小值、平均值、总和）-蒲公英云

Java8 List统计（最大值，最小值、平均值、总和）

核心功能代码：

Integer sum = list.stream().mapToInt(User::getAge).sum();
        System.out.println("年龄总和：" +sum);
        Integer max = list.stream().mapToInt(User::getAge).max().orElse(0);
        System.out.println("年龄 最大：" + max);
        Integer min = list.stream().mapToInt(User::getAge).min().orElse(0);
        System.out.println("年龄 最小：" + min);
        Double average = list.stream().mapToInt(User::getAge).average().orElse(0l);
        System.out.println("年龄 平均：" + df.format(average));

Java8 Stream除了支持Int类型，还支持double 类型和long类型

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学生年龄实例：

package com.digipower.test;
import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class ListTest {
    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<User>();
        for (int i = 1; i <= 5; i++) {
            int age = random.nextInt(10) + 5;// 随机年龄：10-15
            User u = new User(String.valueOf(i), "用户-" + i, age);
            list.add(u);
        }
        Integer sum = list.stream().mapToInt(User::getAge).sum();
        System.out.println("年龄总和：" +sum);
        Integer max = list.stream().mapToInt(User::getAge).max().orElse(0);
        System.out.println("年龄 最大：" + max);
        Integer min = list.stream().mapToInt(User::getAge).min().orElse(0);
        System.out.println("年龄 最小：" + min);
        Double average = list.stream().mapToInt(User::getAge).average().orElse(0l);
        System.out.println("年龄 平均：" + df.format(average));
    }
    static class User {
        private String id;
        private String name;
        private int age;
        public String getId() {
            return id;
        }
        public void setId(String id) {
            this.id = id;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public int getAge() {
            return age;
        }
        public void setAge(int age) {
            this.age = age;
        }
        public User(String id, String name, int age) {
            super();
            this.id = id;
            this.name = name;
            this.age = age;
        }
    }
}

效果截图：

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溫馨提示：針對金融数据类型BigDecimal，求和方式必须使用Stream 类中的reduce函数

学生余额实例：

package com.digipower.test;
import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import java.util.Random;
public class ListTest {
    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<User>();
        for (int i = 1; i <= 5; i++) {
            int age = random.nextInt(10) + 5;// 随机年龄：10-15
            User u = new User(String.valueOf(i), "用户-" + i, age);
            double balance = random.nextDouble() * 100 + 100;//随机金额：100-200
            u.setBalance(new BigDecimal(balance).setScale(BigDecimal.ROUND_HALF_UP, 2));
            list.add(u);
        }
        Integer sum = list.stream().mapToInt(User::getAge).sum();
        System.out.println("年龄总和：" +sum);
        Integer max = list.stream().mapToInt(User::getAge).max().orElse(0);
        System.out.println("年龄 最大：" + max);
        Integer min = list.stream().mapToInt(User::getAge).min().orElse(0);
        System.out.println("年龄 最小：" + min);
        Double average = list.stream().mapToInt(User::getAge).average().orElse(0l);
        System.out.println("年龄 平均：" + df.format(average));
        BigDecimal add = list.stream().map(User::getBalance).reduce(BigDecimal.ZERO, BigDecimal::add);
        System.out.println("金额 总和：" + df.format(add));
        Optional<User> maxBalance = list.stream().max((u1, u2) -> u1.getBalance().compareTo(u2.getBalance()));
        System.out.println("金额 最高：" + df.format(maxBalance.get().getBalance()));
        Optional<User> minBalance = list.stream().min((u1, u2) -> u1.getBalance().compareTo(u2.getBalance()));
        System.out.println("金额 最低：" + df.format(minBalance.get().getBalance()));
    }
    static class User {
        private String id;
        private String name;
        private int age;
        private BigDecimal balance;
        public String getId() {
            return id;
        }
        public void setId(String id) {
            this.id = id;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public int getAge() {
            return age;
        }
        public void setAge(int age) {
            this.age = age;
        }
        public BigDecimal getBalance() {
            return balance;
        }
        public void setBalance(BigDecimal balance) {
            this.balance = balance;
        }
        public User(String id, String name, int age) {
            super();
            this.id = id;
            this.name = name;
            this.age = age;
        }
    }
}