Question

Given the following code:

Class User{   Task m_Task;     public function getTask('Do work') { return m_Task; } }  Class Project{   Task m_Task;     public function getTask('Do work') { return m_Task; } }  Class Task {   private m_Name;   public Task(name) { m_Name = name; } }  Class Evil {   new Task = Error } 

In a language that does not support multiple inheritance, nested classes, or private classes, (private constructor not an option), how can you design a requirement that Task is only ever instantiated through User or Project? Ideally using only language constructs instead of code. Is there a design pattern?

Answer 1

Not quite an answer, you can construct a task from elsewhere but you need a valid task instance to do it..

public class Task {    public Task (User u, String name)    {      if (u==null) throw new UnsupportedOperationException('that's cheating');      this.name=name;    } } 

Utlimately, if you’re creating the requirement that Task be external to user then something else needs to be able to load task’s constructor so I don’t think it’s possible.

What’s the purpose of this question? Does this relate in any way to some real-world situation?