【Optional】1. Map and ifpresent 2 Ofnullable and orelse

 1) Example 1

package org.example.testOptional;

import lombok.Data;
import lombok.ToString;

import java.util.Optional;

public class Main {

    public static Optional<A> getOpA() {
        return Optional.ofNullable(null);
    }

    public static void main(String[] args) {
        getOpA().map(a -> a.getB())
                .ifPresent(a -> {
                    System.out.println(a);
                });
    }
}

@Data
@ToString
class A {
    private String desc = "aaa";
    private int b = 1;
}

2) Example 2

package org.example.testOptional;

import java.util.Optional;

public class UnitObject {
    private int id = 1;

    public UnitObject() {

    }

    public UnitObject getOwner() {
        return null;
    }

    public UnitObject getOwnerOrSelf() {
        //  Find the owner , If the master can't find it, he is himself 
        UnitObject o = Optional.ofNullable(getOwner()).orElse(this);
        return o;
    }

    @Override
    public String toString() {
        return "Main2{" +
                "id=" + id +
                '}';
    }

    public static void main(String[] args) {
        UnitObject unitObject = new UnitObject().getOwnerOrSelf();
        System.out.println(unitObject);

    }
}

/*
Main2{id=1}
 */