Design Patterns Java™ Workbook

Appendix B. Solutions

SOLUTION 12.3....................................................................................................................................

A. A MachineComponent object may have an explicitly assigned responsible person. If

it doesn't, it passes the request to its parent:

public Engineer getResponsible()

{

if (responsible != null)

{

return responsible;

}

if (parent != null)

{

return parent.getResponsible();

}

return null;

}

B. The code for Tool.getResponsibility() reflects the statement that "tools are

always assigned to tool carts":

public Engineer getResponsible()

{

return toolCart.getResponsible();

}

C. The ToolCart code reflects the statement that "tool carts have a responsible

engineer":

public Engineer getResponsible()

{

return responsible;

}

SOLUTION 12.4....................................................................................................................................

Your solution should look something like Figure B.17. Your constructors should allow
Machine and MachineComposite objects to be instantiated with or without an assigned
engineer. Whenever a MachineComponent object does not have an assigned engineer, it
can get a responsible engineer from its parent.