Java Reference
In-Depth Information
System.out.print(s+" ");
System.out.println();
}
}
The
List<String> ls = new ArrayList<>();
assignment reveals a
couple of items to note:
• I've declared variable
ls
to be of
List<String>
interface type, and have
assigned to this variable a reference to an instance of the
ArrayList
class
thatimplementsthisinterface.WhenworkingwiththeCollectionsFramework,
it is common practice to declare variables to be of interface type. Doing so
eliminates extensive code changes when you need to work with a different
implementation class; for example,
List<String> ls = new
LinkedList<>();
. Check out
Chapter 2
's “Why Use Interfaces?” section
for more information about this practice.
• The
diamond operator
<>
(whichisnewinJava7)reducesverbositybyforcing
the compiler to infer actual type arguments for the constructors of generic
classes. Without this operator, I would need to specify
String
as the actu-
al type argument passed to
ArrayList<E>
, resulting in the more verbose
List<String> ls = new ArrayList<String>();
instead of the
shorter
List<String> ls = new ArrayList<>();
.(Idon'tregardthe
diamondoperatorasatrueoperator,whichiswhyIdon'tincludeitin
Chapter
The
dump()
method's enhanced for statement uses
iterator()
,
hasNext()
,
and
next()
behind the scenes.
When you run this application, it generates the following output:
ls: Sun Mon Tue Wed Thu Fri Sat
ls: Sun Mon Tue Wednesday Thu Fri Sat
ls: Sun Mon Tue Wednesday Thu Sat
LinkedList
The
LinkedList
class provides a list implementation that is based onlinked nodes.
Becauselinksmustbetraversed,accesstothelist'selementsisslow.However,because
onlynodereferencesneedtobechanged,insertionsanddeletionsofelementsisfast.(I
will introduce you to nodes later in this chapter.)
LinkedList
supplies two constructors:
