避免NPE问题的解决方案之一 --- Optional类

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本文深入探讨了Java8中Optional类的使用，旨在解决NullPointException问题，通过具体示例展示了如何创建空Optional实例，以及如何使用orElse和map方法进行默认值设定和多级判断。

Optional类旨在解决NullPointException问题。 Java 8 doc

1. 创建空Optional类

Optional<Staff> empty = Optional.empty();

2. 简单应用

2.1 准备的类



    public class Staff {
        String name;
        Integer age;
        Department department;

        public Staff(){

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

    public class Department {
        String name;

        public Department(){

        }
        public Department(String name){
            this.name=name;
        }

        ... //getter setter
    }

2.2 取默认值、单级判断

    @Test
    void optionalTest(){

        System.out.println("--------------------------Default Value-----------------------");
        Staff staff = null;
        Staff staffOptional = Optional.ofNullable(staff).orElse(new Staff("Jerome",12));
        System.out.println(staffOptional);

        System.out.println("------------------------Single Level-------------------------");
        String staffName = Optional.ofNullable(staff).map(s -> s.getName()).orElseGet(() -> "Anonymity");
        System.out.println(staffName);
    }

显示结果

--------------------------Default Value-----------------------
*$Staff@61dd025

------------------------Single Level-------------------------
Anonymity

2.3 多级判断

    @Test
    void optionalTest(){
        System.out.println("--------------------------Default Value-----------------------");
        Staff staff = null;
        Staff staffOptional = Optional.ofNullable(staff).orElse(new Staff("Jerome",12));
        System.out.println(staffOptional);

        System.out.println("-------------------------Multi Level------------------------");
        Department department = new Department("IT");
        staffOptional.setDepartment(department);
        staffName = Optional.ofNullable(staffOptional).map(s -> s.getDepartment()).map(d-> d.getName()).orElse("Anonymity");
        System.out.println(staffName);
    }

显示结果

--------------------------Default Value-----------------------
com.sevnight.zeus.myths.ZeusMythsApplicationTests$Staff@61dd025

-------------------------Multi Level------------------------
IT