@FunctionalInterface
public interface IPlay {

    String   show(String msg);

    default  String  make(){

        return "make";
    }

}

public class Person {

     private  String  userName;
     private  String  password;

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}
 

import java.util.Optional;

public class Main {

    public static void main(String[] args) {

        IPlay  play1 = new IPlay() {
            @Override
            public String show(String msg) {
                return "原來的寫法如下";
            }
        };

        // 現在的寫法
        IPlay  play = (msg)->{return  msg;};
        String msg  = play.show("我是訊息");
        System.out.println(msg);


        msg =  play.make();
        System.out.println(msg);


        // Optional 更多的體現是一個容器，包含null的一個容器。通過他去判斷。

        Person person = null;
        Optional<Person>  optional = Optional.ofNullable(person);
        boolean flag = optional.isPresent();
        System.out.println(flag);

        if (flag){
             person = optional.get(); // 獲取物件進行處理。
             System.out.println(person);
        }else{
            System.out.println("person is null");
        }

    }
}