Immutable beans in Java

public interface DateBean {
    public Date getDate();
    public DateBean getImmutableInstance();
    public DateBean getMutableInstance();
}

public class ImmutableDate implements DateBean {
    private Date date;

ImmutableDate(Date date) {
	this.date = new Date(date.getTime());
}

public Date getDate() {
	return new Date(date.getTime());
}

	public DateBean getImmutableInstance() {
		return this;
	}

	public DateBean getMutableInstance() {
		MutableDate dateBean = new MutableDate();
		dateBean.setDate(getDate());
		return dateBean;
	}
}

public class MutableDate implements DateBean {
    private Date date;

public Date getDate() {
	return date;
}

public void setDate(Date date) {
	this.date = date;
}

public DateBean getImmutableInstance() {
	return new ImmutableDate(this.date);
}

	public DateBean getMutableInstance() {
		MutableDate dateBean = new MutableDate();
		dateBean.setDate(getDate());
		return dateBean;
	}
}

public class ImmutableDate implements DateBean
{
   private DateBean delegate;

   public ImmutableDate(DateBean d)
   {
      this.delegate = d;
   }

   public Date getDate()
   {
      return delegate.getDate();
   }
}

public interface DateBean {
    public Date getDate();
}

public class ImmutableDate implements DateBean {
    private final long date;

    ImmutableDate(long date) {
       this.date = date;
    }

    ImmutableDate(Date date) {
       this(date.getTime());
    }

    ImmutableDate(DateBean bean) {
       this(bean.getDate());
    }

    public Date getDate() {
         return new Date(date);
    }
}


public class MutableDate implements DateBean {
    private long date;

    MutableDate() {}

    MutableDate(long date) {
       this.date = date;
    }

    MutableDate(Date date) {
       this(date.getTime());
    }

    MutableDate(DateBean bean) {
       this(bean.getDate());
    }

    public Date getDate() {
        return new Date(date);
    }

    public void setDate(Date date) {
        this.date = date.getTime();
    }

}

public interface User{

  long getId();

  String getName();

  int getAge();

}

public interface MutableUser extends User{

  void setName(String name);

  void setAge(int age);

}

public void validateUser(User user){
  if(user.getName() == null) ...
}

public void updateUserAge(MutableUser user, int age){
  user.setAge(age);
}