Optional类的filter方法

最新推荐文章于 2025-05-01 09:30:00 发布

原创最新推荐文章于 2025-05-01 09:30:00 发布 · 7.1k 阅读

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CC 4.0 BY-SA版权

文章标签：

#filter #stream #java #lambda

filter方法可对Optional内对象进行过滤。

1. 准备类

    public class Staff {
        String name;
        Integer age;
        public Staff(){

        }
        public Staff(String name, Integer age){
            this.name = name;
            this.age = age;
        }
        ... // getter setter
       
    }

2. 示例

    @Test
    void filterOptionalTest(){
        ArrayList<Staff> staffList = new ArrayList<>();
        staffList.add(new Staff("Jerome",28));
        staffList.add(new Staff("Chris",44));

        System.out.println("----------------List Stream Filter--------------------------");
        String name = staffList.stream().filter(s -> s.getAge() < 30).map(s -> s.getName()).findFirst().orElseGet(() -> "Null");
        System.out.println(name);

        System.out.println("----------------Optional Filter--------------------------");
        name = Optional.ofNullable(staffList.get(0)).filter(s -> s.getAge() > 30).map(s -> s.getName()).orElse("Null");
        System.out.println(name);

        name = Optional.ofNullable(staffList.get(1)).filter(s -> s.getAge() > 30).map(s -> s.getName()).orElse("Null");
        System.out.println(name);

    }

显示

----------------List Stream Filter--------------------------
Jerome
----------------Optional Filter--------------------------
Null
Chris