Aug 24

Is Implementing Equals and HashCode Enough ?

Basic, Java, performance 4 Comments »

As per Joshua Bloch Effective Java Second Edition, Item 9 Always override hashCode when you override equals.

“You must override hashCode in every class that overrides equals. Failure to do so
will result in a violation of the general contract for Object.hashCode, which will
prevent your class from functioning properly in conjunction with all hash-based
collections, including HashMap, HashSet, and Hashtable.”

Another Important Line from the Effective Java “In hashCode method you must exclude any fields that are not used in equals comparisons,
or you risk violating the second provision of the hashCode contract”(To refer to contract look into Object.java (javadoc))

I want to add to this and say :

Always compareTo method should reflect same logic as you have in equals. Continue reading »

Jul 07

Querying it jQuery way: getElementsByClassName

Web 2.0, performance 8 Comments »

I have got a JSP page which after being rendered needs to call an onload event to look for all divs (believe me there are many of them) having some style class assigned to them and hide them from view. This is one of those kitchen sink problem that came back to haunt me making me realize that JS DOM API doesn’t give me anything to fetch elements containing a class as one of its style attributes.

I came across one of the implementation which goes like this: Continue reading »

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Jun 19

J2EE Applications and Clusters

performance 4 Comments »

Issues in porting existing Applications on Clustered Environments

The ideas mentioned below are based on the practical experience of porting an existing application over a clustered environment. The work around and the solutions mentioned below should not be taken as “best practice guidelines” but possible quick fixes which may be needed to make sure that the application can run in a stable fashion without causing serious issues though with some trade off on scalability.

Environmental Setup of Cluster

The typical cluster being discussed here is not application severs cluster where the App servers are started in a clustered mode. Here multiple instances of App servers were started on different machines connecting to the same DB and a load balancer was placed in front of them for receiving requests and forwarding it to one of the App Server instances. Continue reading »

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May 05

String Concatenation and Optimizations

performance No Comments »

A smarter brain than mine at work, pointed out this interesting article to me.
Java String Performance testing
It talks about string performance testing. I could make sense of most of the observations made in this test and thought of sharing it.

In short the test compares string operations like “+”, “new String” and then “+”, “+” with fields and then StringBuffer append. One of the conclusions of the test is

the ‘+’ operator is not evil when used with Strings

I agree with this statement and a look at the generate byte code pretty much convinces us of so. But, a word of caution here, it always makes sense to check this on our target compiler before committing to it. Continue reading »

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