Design Patterns Java™ Workbook

Chapter 5. Composite

CHALLENGE 5.3

For each method declared by MachineComponent, give recursive definitions for

MachineComposite and nonrecursive definitions for Machine.

Method Class Definition

getMachineCount() MachineCompositeReturn the sum of the

counts for each component

in components.

Machine Return 1.

isCompletelyUp() MachineComposite??

Machine ??

stopAll() MachineComposite??

(^) Machine ??
getOwners() MachineComposite??
Machine ??
getMaterial() MachineComposite??
Machine^ ??

Trees in Graph Theory................................................................................................................................

In a composite structure, we can say that a node that holds references to other nodes is a tree.
However, this definition is a bit loose. To be more precise, we can apply a few terms from
graph theory to object modeling. We can start by drawing an object model as
a graph—a collection of nodes and edges—with objects as nodes and object references as
edges.

Consider an object model of an assay, or analysis, of a batch of a chemical. The Assay class
has a batch attribute of type Batch, and the Batch class has a chemical attribute of type
Chemical. Suppose that a particular Assay object a has a batch attribute that refers to
a Batch object b. Suppose too that the chemical attribute of the Batch object b refers to
a Chemical c. Figure 5.3 shows two alternative diagrams for this object model.

Figure 5.3. The two UML diagrams here show alternative representations of the same

information: Object a refers to object b, and object b refers to object c.