container
Interface Decorable

All Known Subinterfaces:

DirectedEdge, Vertex

All Known Implementing Classes:

HashDecorable, StoredDirectedEdge, StoredVertex

public interface Decorable

In addition to storing its usual data, a class might allow users to "decorate" it with some extra temporary data. For example, we might say that a vertex of a graph is colored red or black, or that it is marked as visited, or that it stores a level number or a back pointer.

A Decorable object can store any number of extra temporary fields. Each is like a temporary instance variable, called an "attribute," that we can add or remove from the object. For example, the object's COLOR attribute could be "red" or "black," or the object might not have a COLOR attribute right now.

To make a new attribute, COLOR, use the constructor for the Attribute class. Now you can do p.put(COLOR,RED) and p.get(COLOR) for a position p. Here RED would be an object of class Color, or perhaps just the string "red" if you are too lazy to make such a class.

The textbook discusses decorations (section 12.3) and gives examples (e.g., code fragment 12.4), but it does not use an Attribute class as we do. See Attribute.java for discussion. Also, the textbook sticks to decorable positions, whereas any object could implement Decorable interface given here.

Method Summary

java.lang.Object	get(container.Attribute a)
boolean	has(container.Attribute a) Does this object currently have any value for this attribute?
java.lang.Object	put(container.Attribute a, java.lang.Object o) Makes this object store o as the value of attribute a.
java.lang.Object	remove(container.Attribute a) Removes attribute a and its associated value from this object.

Method Detail

get

public java.lang.Object get(container.Attribute a)

Returns:

this object's value for attribute a, or null if no such value is currently stored.

has

public boolean has(container.Attribute a)

Does this object currently have any value for this attribute? (Asking has(a) is clearer than asking get(a)!=null, and it distinguishes between no value and a value that happens to be null.)

put

public java.lang.Object put(container.Attribute a,
                            java.lang.Object o)

Makes this object store o as the value of attribute a.

Returns:

previous value, or null if there was none

remove

public java.lang.Object remove(container.Attribute a)

Removes attribute a and its associated value from this object.

Returns:

previous value, or null if there was none