[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: String interning (WAS: SAX2/Java: Towards a final form)
Miles Sabin wrote: > Tyler Baker wrote, > > For most documents, making a call to String.intern() > > 50-100 times in a 100KB document is a lot less expensive than > > doing: > > > > if (x.equals("foo") { > > > > } > > else if (x.equals("bar") { > > > > } > > etc... > > > > As opposed to: > > > > if (x == "foo") { > > > > } > > else if (x == "bar) { > > > >} > > etc. > > > > Calling the equals method can get expensive for large case > > statements. > > Sure ... so Don't Do That (tm) ... > > If you've got what's effectively a huge case statement then > use a lookup table ... a HashMap or a trie of some sort or > another. Either of those will outperform a large number of > chained String.equals() calls or == tests. If you are using interned strings, a HashMap becomes much faster anyways. But that will not outperform a bunch of identity tests as they are one of the fastest operations in Java. As someone who has written an XML Parser before, I can tell you and so can many of the other people on this list, that at the application level it is much faster to deal with interned strings in case logic, than otherwise. Even if you choose not to do identity tests in your case logic, using a HashMap or just using String.equals() will be much faster because the implementation of the String.equals() method goes like this: public boolean equals(Object anObject) { if (this == anObject) { return true; } if ((anObject != null) && (anObject instanceof String)) { String anotherString = (String)anObject; int n = count; if (n == anotherString.count) { char v1[] = value; char v2[] = anotherString.value; int i = offset; int j = anotherString.offset; while (n-- != 0) { if (v1[i++] != v2[j++]) { return false; } } return true; } } return false; } As you can see an identity test is done right off the bat so if you make a call like this: if (foo.equals("x")) { } And foo == "x", then your only additional overhead to a straight identity test is the dynamic method invocation of String.equals(). Tyler xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ or CD-ROM/ISBN 981-02-3594-1 Please note: New list subscriptions now closed in preparation for transfer to OASIS.
|
PURCHASE STYLUS STUDIO ONLINE TODAY!Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced! Download The World's Best XML IDE!Accelerate XML development with our award-winning XML IDE - Download a free trial today! Subscribe in XML format
|