Java Reference
In-Depth Information
element in the class to occur more than once. Classes that implement the
List<T>
interface have their elements ordered on a list, so there is a zeroth element, a first
element, a second element, and so forth. A class that implements the
List<T>
interface
allows elements to occur more than once. The
ArrayList<T>
class implements the
List<T>
interface.
The
Set<T>
interface has the same method headings as the
Collection<T>
interface, but in some cases the semantics (intended meanings) are different. For
example, the semantics of adding new elements to the set do not allow duplicates. The
add methods are described in Display 16.3. A complete list of the
Set<T>
interface is
given in Appendix 5 .
Display 16.3
Adding Elements in the
Set<T>
Interface
The
Set<T>
interface is in the
java.util
package.
The
Set<T>
interface extends the
Collection<T>
interface and has all the same method headings
given in Display 16.2. However, the semantics of the add methods vary as described below.
public boolean
add(T element)
(Optional)
If
element
is not already in the calling object,
element
is added to the calling object and
true
is
returned. If
element
is in the calling object, the calling object is unchanged and
false
is returned.
public boolean
addAll(Collection<? extends > collectionToAdd)
(Optional)
Ensures that the calling object contains all the elements in
collectionToAdd
. Returns
true
if the
calling object changed as a result of the call; returns
false
otherwise. Thus, if
collectionToAdd
is a
Set<T>
, then the calling object is changed to the union of itself with
collectionToAdd
.
The
List<T>
interface has more method headings than the
Collection<T>
interface,
and some of the methods inherited from the
Collection<T>
interface receive somewhat
different semantics. For example, the semantics of adding new elements to the set allow
duplicates, and rules must be made about which element should be removed when there
are duplicates. These methods, along with new method definitions, are described in
Display 16.4 . A complete list of the
List<T>
interface is given in Appendix 5 .
Display 16.4
Selected Methods in the
List<T>
Interface
(part 1 of 3)
The
List<T>
interface is in the
java.util
package.
The
List<T>
interface extends the
Collection<T>
interface.
ADDING AND REMOVING ELEMENTS
public boolean
add(T element)
(Optional)
Adds element to the end of the calling object's list. Normally returns
true
. Returns
false
if the
operation failed, but if the operation failed, something is seriously wrong and you will probably
get a run-time error anyway.
