Java Reference
In-Depth Information
Theframework's implementation classes alsoinclude theabstract AbstractCol-
lection , AbstractList , AbstractSequentialList , AbstractSet , Ab-
stractQueue ,and AbstractMap classes.Theseclassesofferskeletalimplementa-
tions of the core interfaces to facilitate the creation of concrete implementation classes.
Finally, the framework provides two utility classes: Arrays and Collections .
Comparable Versus Comparator
Acollectionimplementationstoresitselementsinsome order (arrangement).Thisorder
numerical, or chronological).
natural ordering .Forexample,thenaturalorderingof String objectsis lexicographic
or dictionary (also known as alphabetical) order.
Acollectioncannotrelyon equals() todictatenaturalorderingbecausethismeth-
plement the java.lang.Comparable<T> interface andits int compareTo(T
o) method.
Note Accordingto Comparable 'sJavadocumentation,thisinterfaceisconsidered
to be part of the Collections Framework, even though it is a member of the
java.lang package.
A sorted collection uses compareTo() to determine the natural ordering of this
method's element argument o in a collection. compareTo() compares argument o
with the current element (which is the element on which compareTo() was called)
and does the following:
• It returns a negative value when the current element should precede o .
• It returns a zero value when the current element and o are the same.
• It returns a positive value when the current element should succeed o .
When you need to implement Comparable 's compareTo() method, there are
Chapter 2 for implementing the equals() method:
compareTo() must be reflexive :Foranynonnullreferencevalue x , x .com-
pareTo( x ) must return 0.
compareTo() must be symmetric :Foranynonnullreferencevalues x and y ,
x .compareTo( y ) == -y.compareTo(x) must hold.
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