Java8 Optional为空处理

package com.example.cesium.utils;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;

import java.util.Optional;


public class OptionalTest {

    public static void main(String[] args) {
        //1使用前
        Student student = new Student("charkey", 20, 50, new Address());
        //student = null;
        if (student != null) {
            String name = student.getName();
            System.out.println("name = " + name);
        }
        //1使用后
        Optional.ofNullable(student).map(Student::getName).ifPresent(System.out::println);

        //2使用前
        if (student == null) {
            new Student();
        } else {
            student = student;
        }
        //2使用后
        Student student1 = Optional.ofNullable(student).orElseGet(() -> new Student());
        System.out.println("student1 = " + student1);

        //3使用前
        if (student == null) {
            throw new RuntimeException("1.用户名为空");
        }
        //3使用后
        //student = null;
        Optional.ofNullable(student).orElseThrow(() -> new RuntimeException("2.用户名为空"));

        //4使用前
        if (student != null) {
            int sore = student.getScore();
            if (sore < 60) {
                System.out.println("1.不及格处理。。。");
            }
        }
        //4使用后
        Optional.ofNullable(student).map(Student::getScore).filter(score -> score < 60).ifPresent(stu -> {
            System.out.println("2.不及格处理。。。");
        });
        Optional.ofNullable(student).filter(stu -> stu.getScore() < 60).orElseGet(() -> {
            System.out.println("2.及格处理。。。");
            return new Student();
        });

        //5使用前
        Address address1 = new Address("北京", "001", new Country("中国", "000"));
        student = new Student("charkey", 20, 50, address1);
        if (student != null) {
            Address address = student.getAddress();
            if (address != null) {
                Country city = address.getCountry();
                if (city != null) {
                    if (city.getCode() != null) {
                        String code = city.getCode().toLowerCase();
                        System.out.println(code);
                    }
                }
            }
        }
        //5使用后
        Optional.ofNullable(student).flatMap(s -> Optional.ofNullable(s.getAddress())).flatMap(s -> Optional.ofNullable(s.getCountry())).map(Country::getCode).ifPresent(System.out::println);

    }


    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    @ToString
    public static class Student {
        private String name;
        private Integer age;
        private Integer score;
        private Address address;
    }

    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    public static class Address {
        private String name;
        private String code;
        private Country country;
    }

    @Data
    @AllArgsConstructor
    @NoArgsConstructor
    public static class Country {
        private String name;
        private String code;
    }


}