How to implement a one-to-many relationship in a database or object-oriented model?

A "one-to-many" relationship in a database is implemented using a foreign key in the "many" table that references the primary key of the "one" table.

In an object-oriented model in Java, this is usually implemented as:

public class Parent {
    private Long id;
    private List<Child> children = new ArrayList<>();

    // getters and setters
}

public class Child {
    private Long id;
    private Parent parent;

    // getters and setters
}

If using JPA/Hibernate, the relationship can be described with annotations:

@Entity
public class Parent {
    @Id
    private Long id;

    @OneToMany(mappedBy = "parent")
    private List<Child> children;
}

@Entity
public class Child {
    @Id
    private Long id;

    @ManyToOne
    @JoinColumn(name = "parent_id")
    private Parent parent;
}

Thus, one Parent object can have many associated Child objects.