Java class designe suggestion

I have some concussion to make proper design for the following interface and class. The requirement is the following:-

public interface Entity {
// Returns entity name
String getName();
// Returns a unique identifier
String getID();
// Returns the sub-entities of this entity
Set<Entity> getSubEntities();
// Returns a set of key-value data belonging to this entity
Map<String,String> getData();
}

public class SubEntity implements Entity {

private String ID;
private String name;
private int price;
private Set<Entity> sbuEntities;

public SubEntity(){
    ID = UUID.randomUUID().toString();
}

public SubEntity(String name, int price) {
    this.name = name;
    this.price = price;
    this.ID = UUID.randomUUID().toString();
}

public void setId(String id) {
    this.ID = id;
}

public String getName() {
    return name;
}

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

public int getPrice() {
    return price;
}

public void setPrice(int price) {
    this.price = price;
}

public String getID() {
    return ID;
}

public void addSubEntity(Entity entity){
    if(sbuEntities == null){
        sbuEntities = new HashSet<>();
    }
    sbuEntities.add(entity);
};

public Set<Entity> getSubEntities(){
    return sbuEntities;
}

public Map<String, String> getData() {
    if(sbuEntities == null){
        sbuEntities = new HashSet<>();
    }
    return sbuEntities.stream()
            .collect(Collectors.toMap(Entity::getID,
                    Object::toString));
}

public String toString() {
    return "SubEntity{" +
            "id='" + ID + '\'' +
            ", name='" + name + '\'' +
            ", price=" + price +
            '}';
}
}

There could be many types of SubEnitity that implement this interface. Also, every SubEnitity should have a Set as Set subentities or Set sbuEntities. I have confusion about the Set. Should I keep inside the SubEntity or outside. I would like to know your opinion with possible pros an cons.

Will this be of any help ?

Sorry, i don’t know much about JAVA and all this, so i just googled your question and found this link

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