Java utilities - JavaTech: An Introduction to Scientific and Technical Computing with Java - page 329

// Error: the object returned is of the Date type, not a
// String object.
String date = (String) list.lastElement ();
Yo u can use the operator instanceof to query the object for what type of object
it is:
Object o = list.lastElement ();
if (o instanceof String)
String date = (String) o;
else if (o instanceof Date)
Date aDate = (Date) o;
The Vector class has a number of other methods, such as a search for the index
number of a particular object in the vector, as in
int i = list.indexOf ("Yet another string");
A Vector can also return an Enumeration .An Enumeration provides for
a one-time scan through a list of Objects .(We note that an Enumeration has
no relationship at all with the enumerated type of J2SE 5.0, which is explained
in Section 10.9.)
Enumeration e = list.elements ();
while (e.hasMoreElements ()) {
System.out.println (e.nextElement ().toString ());
}
After hasMoreElements() returns false , the Enumeration cannot be used
again.
With the Java 1.2 Collections Framework (see Section 10.6) came a pre-
ferred alternative to Enumeration called Iterator . The Iterator class
differs from Enumeration in that the iterator permits removing one or more
elements from the Vector without damaging the Iterator .Inaddition,
the iterator methods hasNext() and next() have more concise names than
the corresponding methods hasMoreElements() and nextElement() in
Enumeration .Weexplain more about the Iterator interface in Section 10.6.
10.4 Hashtable , Properties , and HashMap
The Hashtable class provides associative arrays with key-value pairings. Pre-
sentation of the key retrieves the value. The keys and values must be objects,
not primitive type values. If you want to include numerical values, then use the
corresponding wrapper classes such as Integer for an int value (or rely on
the autoboxing support in J2SE 5.0 as explained in Chapter 3).