Lambda常用表达式

看到这个公众号  Java技术前线 ，有所感想，于是把目前工作中常用的几个列出来！

常用表达式：

• collect(Collectors.toList())  将流转换为list。还有toSet()，toMap()等

• filter 过滤筛选

• max和min  在集合中求最大或最小值

• count  统计，结合filter使用

• sorted 排序 默认升序

import com.bigdata.bigdata.entity.User;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.Optional;
import java.util.Set;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * @Auther: lirui
 * @Date: 2020/11/1 0:12
 * @Description: Lambda测试
 */
public class TestLambda {

    public static void main(String[] args) {

        List userList = Stream.of(new User("肖战", "男", 30),
                new User("王一博", "男", 24),
                new User("李易峰", "男", 34)).collect(Collectors.toList());
        System.out.println(userList);

        Set stringSet = Stream.of("肖战","王一博","肖战").collect(Collectors.toSet());
        System.out.println(stringSet);

        List names = userList.stream().map(user -> user.getName())
                .collect(Collectors.toList());
        System.out.println(names);

        String nameStr = userList.stream().map(User::getName)
                .collect(Collectors.joining(",","",""));
        System.out.println(nameStr);

        List users=new ArrayList<>();
        users.add(new User("肖战", "男", 30));
        users.add(new User("王一博", "男", 24));
        users.add(new User("李易峰", "男", 34));

        //查询年龄大于25的，年龄升序排序，
        List list = users.stream()
                .filter(stu -> stu.getAge() > 25)
                .sorted(Comparator.comparing(User::getAge))
                .collect(Collectors.toList());
        //[User{name='肖战', sex='男', age=30}, User{name='赵丽颖', sex='女', age=30}, User{name='李易峰', sex='男', age=34}]
        System.out.println(list);

        //查询年龄大于25的，年龄升序排序，根据性别进行分组
        Map> list1 = users.stream()
                .filter(stu -> stu.getAge() > 25)
                .sorted(Comparator.comparing(User::getAge))
                .collect(Collectors.groupingBy(User::getSex));
        //{女=[User{name='赵丽颖', sex='女', age=30}], 男=[User{name='肖战', sex='男', age=30}, User{name='李易峰', sex='男', age=34}]}
        System.out.println(list1);

        //在第一个字段数据相同的对第二个字段进行比较
        //对age升序，name降序
        List collect = users.stream().filter(stu -> stu.getAge() > 25).sorted(Comparator.comparingInt(User::getAge)
                .thenComparing(Comparator.comparing(User::getName).reversed()))
                .collect(Collectors.toList());
        System.out.println(collect);
        //对age降序，name升序
        List collect1 = users.stream().filter(stu -> stu.getAge() > 25).sorted(Comparator.comparingInt(User::getAge).reversed()
                .thenComparing(Comparator.comparing(User::getName)))
                .collect(Collectors.toList());
        System.out.println(collect1);
        //对age降序，name降序
        List collect2 = users.stream().filter(stu -> stu.getAge() > 25).sorted(Comparator.comparingInt(User::getAge)
                .thenComparing(Comparator.comparing(User::getName)).reversed())
                .collect(Collectors.toList());
        System.out.println(collect2);
        //对age升序，name升序
        List collect3 = users.stream().filter(stu -> stu.getAge() > 25).sorted(Comparator.comparingInt(User::getAge)
                .thenComparing(Comparator.comparing(User::getName)))
                .collect(Collectors.toList());
        System.out.println(collect3);


        Optional max = users.stream()
                .max(Comparator.comparing(stu -> stu.getAge()));
        Optional min = users.stream()
                .min(Comparator.comparing(stu -> stu.getAge()));
        //判断是否有值
        if (max.isPresent()) {
            System.out.println(max.get());
        }
        if (min.isPresent()) {
            System.out.println(min.get());
        }

        long count = users.stream().filter(s1 -> s1.getAge() > 25).count();
        System.out.println("年龄大于25岁的人数是：" + count);


        Predicate predicate = x -> x > 24;
        User user = new User("肖战", "男", 30);
        System.out.println("肖战的年龄大于24吗？：" + predicate.test(user.getAge()));
    }
}

后面工作中会出现其他信息，会继续补充的