Java How to Program Fourth Edition - DCC

Chapter 21 Collections 1229
public static method header
Collection unmodifiableCollection( Collection c )
List unmodifiableList( List aList )
Set unmodifiableSet( Set s )
SortedSet unmodifiableSortedSet( SortedSet s )
Map unmodifiableMap( Map m )
SortedMap unmodifiableSortedMap( SortedMap m )
Fig. Fig. 21.15 21.15 Unmodifiable wrapper methods.
Software Engineering Observation 21.9
You can use an unmodifiable wrapper to create a collection that offers read-only access to
others, while allowing read–write access to yourself. You do this simply by giving others a
reference to the unmodifiable wrapper while you also retain a reference to the wrapped collection
itself. 21.9
21.11 Abstract Implementations
The collections framework provides various abstract implementations (i.e., “bare bones”
implementations of collection interfaces from which the programmer can quickly “flesh
out” complete customized implementations). These abstract implementations are a thin
Collection implementation called an AbstractCollection, a thin List implementation
with random-access backing called an AbstractList, a thin Map implementation
called an AbstractMap, a thin List implementation with sequential-access
backing called an AbstractSequentialList and a thin Set implementation called
an AbstractSet.
To write a custom implementation, begin by selecting as a base the abstract-implementation
class that best meets your needs. Next, implement each of the class’s abstract
methods. Then, if your collection is to be modifiable, override any concrete methods that
prevent modification.
21.12 (Optional) Discovering Design Patterns: Design Patterns
Used in Package java.util
In this section, we use the material on data structures and collections discussed in Chapters
19, 20 and 21 to identify classes from package java.util that use design patterns. This
section concludes our treatment of design patterns.
21.12.1 Creational Design Patterns
We conclude the discussion of creational design patterns by discussing the Prototype design
pattern.
Prototype
Sometimes, a system must make a copy of an object but will not know that object’s class
until run time. For example, consider the drawing program design of Exercise 9.28—class-
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