高度抽象的集合数据处理

1. 使用Stream流对List进行去重、去偶数，然后查找最大值

import java.util.Arrays;
import java.util.Comparator;

public class Stream1 {
    public static void main(String[] args) {
        int max = Arrays.asList(1,2,2,5,6,8,9)
                .stream()
                //去重
                .distinct()
                //去偶
                .filter(n -> n%2 != 0)
                //取最大
                .max(Comparator.comparing(n -> n))
                .get();
        System.out.println(max);
    }
}

2. 使用Stream流对List进行排序，然后取第一个值

import java.util.Arrays;
import java.util.Comparator;

public class Stream2 {
    public static void main(String[] args) {
        int first = Arrays.asList(1,2,2,5,6,8,9)
                .stream()
                //排序-升序
                .sorted(Comparator.comparing(n -> n))
                //取第一
                .findFirst()
                .get();
        System.out.println(first);

        int first_reversed = Arrays.asList(1,2,2,5,6,8,9)
                .stream()
                //排序-降序
                .sorted(Comparator.comparing(n -> n,Comparator.reverseOrder()))
                .findFirst()
                .get();
        System.out.println(first_reversed);

    }
}

3. 使用Stream流对List进行求平均值、求和

import java.util.Arrays;

public class Stream3 {
    public static void main(String[] args) {
        //求平均值
        double average = Arrays.asList(1,2,2,5,6,8,9)
                .stream()
                //对流中的元素执行一对一的转换
                .mapToInt(n->n)
                //返回流中所有元素的平均值
                .average()
                .getAsDouble();
        System.out.println(average);

        //求和
        int sum = Arrays.asList(1,2,2,5,6,8,9)
                .stream()
                .mapToInt(n->n)
                .sum();
        System.out.println(sum);
    }
}

4. 使用Stream流对List进行排序，按照age从大到小排序

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class Stream4 {
    static class Person{
        int age;
        String name;

        public Person(int age, String name) {
            this.age = age;
            this.name = name;
        }

        public int getAge() {
            return age;
        }

        public void setAge(int age) {
            this.age = age;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        @Override
        public String toString() {
            return "Person{" +
                    "age=" + age +
                    ", name='" + name + '\'' +
                    '}';
        }
    }


    static List<Person> list = Arrays.asList(
            new Person(30,"王五"),
            new Person(33,"张三"),
            new Person(27,"李四")
            );
    public static void main(String[] args) {
        System.out.println("排序前："+list);
        List<Person> personList = list
                .stream()
                .sorted(Comparator.comparing(n->n.getAge()))
                .collect(Collectors.toList());
        System.out.println("排序后："+personList);
    }
}