Guava API學習之Optional 判斷對象是否為null

 

 

import com.google.common.base.Optional;

public class OptionalTest {

    public static void main(String[] args) {
        Student student = new Student();
//        student.setName("loli");
        String name = student.getName();
//        Optional<String> optional = Optional.fromNullable(name);
//        if (optional.isPresent()) {
////            不為空
//            System.out.println(name);
//        } else {
////            為空走這一條
//            System.out.println("null...");
//            student.setName("hJosama");
//        }
//        name = null;
//        optional = Optional.fromNullable(name);
//        if (!optional.isPresent()) {
////            為空直接走這一條
//        } else {
////            不為空
//        }

        if (!Optional.fromNullable(name).isPresent()){
            System.out.println("null...");
            name="hJosama";
        }
        if (Optional.fromNullable(name).isPresent()){
            System.out.println(name);
        }else {
            System.out.println("null...");
        }

    }

    private static class Student {
        String name;

        public String getName() {
            return name;
        }

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

 

        <!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>27.0.1-jre</version>
        </dependency>

 

 

參考：https://www.cnblogs.com/sungang/archive/2014/04/02/3641164.html