Java Reference
In-Depth Information
corresponding flight going the other way. Or, if there is, we may want to associate
different information with it, such as cost.
Like trees, graphs often are implemented using dynamic links, although they
can be implemented using arrays as well.
SELF-REVIEW QUESTIONS
(see answers in Appendix N)
SR 13.15
What do trees and graphs have in common?
SR 13.16
Which structure (a tree or a graph) would be a good choice to repre-
sent each of the following.
a. The directories and files on a computer system.
b. Airplane routes.
c. An “is a friend of” relationship among a group of people.
d. An “is a boss of” relationship in a company.
The Java standard class library contains several classes that represent collec-
tions of various types. These are often referred to as the
Java Collections API
(Application Programming Interface).
Most of the names of the classes in this set indicate both the col-
lection type and the underlying implementation. One example is the
ArrayList
class, which is discussed in some detail in Chapter 5. It
represents a list collection, implemented using an underlying array.
Similarly, the
LinkedList
class represents a list collection with a
dynamically linked internal implementation.
KEY CONCEPT
The Java Collections API defines sev-
eral collection classes implemented
in various ways.
The
Vector
class and the
Stack
class are carried over from earlier Java incarna-
tions, which is why their names aren't consistent with the newer collection classes.
Several interfaces are used to define the collection operations themselves. These
interfaces include
List
,
Set
,
SortedSet
,
Map
, and
SortedMap
. A
Set
is consistent
with its normal interpretation as a collection of elements without duplicates. A
Map
is a group of elements that can be referenced by a key value.
Generics
As we mentioned in Chapter 5 during the discussion of the
ArrayList
class, the
classes in the Java Collections API are implemented as
generic types
, meaning
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