Tech Tips

A note on Design patterns Many times we can see ourselves looking for design patterns to fit the design of a requirement. Of course if the requirement is simple enough to apply any existing design pattern we should do so. This will save us valuable time. In my opinion it is better not to worry about which pattern to apply.But concentrate on the three basic Object oriented principles. 1) Encapsulate what varies 2) Prefer composition over inheritance 3) Program to an interface not to an implementation. If we approach the design with these principles in mind , we don't have to search for patterns. Pattern will emerge itself. Once we apply these principles, we can definitely look whether any of the existing patterns can solve the issue better than the way we thought of. This way our thinking process will improve tremendously and at times we may end up creating a solution which may be better than any available design patterns.

It is interesting and important to understand how strings are handled in Java. The way Java handles or manages strings is little different from other objects. Case1 : String a = "java"; String b= "java"; Does these two strings represent the same object reference ?. The answer is yes they do. Case 2: String c=new String("java"); String d =new String("java"); Does c and d point to the same object reference. The answer is NO . They don't. Now let us see how all these work out. First thing: Java maintains a pool of string constants called literal pool. Infact this pool contains references to string instances in heap. Since Strings are also objects they are also created in the heap. Whenever you put a literal ( example to this is what the variable a represents) in the code, this gets special treatment. When the JVM loads your class where there is a string literal, the VM checks whether there is an existing entry in the string pool for this string ...

Every programmer would have encountered a ClassNotfoundException somewhere in the development lifecycle. Many times we search for reasons why this is happening and i have seen many times people spending long hours to find why this is happening. This is particularly seen with web applications which are deployed in a webserver like tomcat or an app server like Weblogic or JBoss.In the case of a normal desktop java application, this can be fixed by adding the required class or the library that contains the class to the classpath. This way with Java 1.2, classpath classloader will load the class and the issue is fixed. For a web application this may not be as staightforward. Some times i have seen people adding the class to the classpath of the webserver and still getting the error again. Now to identify and fix these issues we need to understand that java supports many types of classloaders. The main one being bootstrap classloader responsible for loading Java API. The other one is the c...