Optional map() and flatMap() difference

MapAndFlatMapTest.java

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

import java.util.Optional;

import static org.assertj.core.api.Assertions.assertThat;

class MapAndFlatMapTest {
    Person dion;

    @BeforeEach
    void setUp() {
        dion = new Person("dion", 26);
    }

    @Test
    void wrapWithOptionalTest() throws Exception {
        Optional<Person> personOptional = Optional.of(dion);
        Optional<Optional<String>> nameOptionalWrapper = personOptional.map(Person::getOptionalName);
        Optional<String> nameOptional = nameOptionalWrapper.orElseThrow(Exception::new);
        String name = nameOptional.orElse("");
        assertThat(name).isEqualTo("dion");

        String name2 = personOptional.flatMap(Person::getOptionalName).orElse("");
        assertThat(name2).isEqualTo("dion");
    }

    @Test
    void normalParameterTest() {
        Optional<Person> personOptional = Optional.of(dion);
        Optional<Integer> integerOptional = personOptional.map(Person::getAge);
        Integer age = integerOptional.orElse(0);
        assertThat(age).isEqualTo(26);

        Integer age2 = personOptional.flatMap(p -> Optional.ofNullable(p.getAge())).orElse(0);
        assertThat(age2).isEqualTo(26);
    }
}

Person.java

import java.util.Optional;

public class Person {
    private final String name;
    private final Integer age;

    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    public Optional<String> getOptionalName() {
        return Optional.ofNullable(this.name);
    }

    public Integer getAge() {
        return this.age;
    }
}