Java Programming Tips

Java Virtual Machine maintains an internal list of references for interned Strings ( pool of unique Strings) to avoid duplicate String objects in heap memory. Whenever the JVM loads String literal from class file and executes, it checks whether that String exists in the internal list or not. If it already exists in the list, then it does not create a new String and it uses reference to the existing String Object. JVM does this type of checking internally for String literal but not for String object which it creates through 'new' keyword. You can explicitly force JVM to do this type of checking for String objects which are created through 'new' keyword using String.intern() method. This forces JVM to check the internal list and use the existing String object if it is already present. e.g. String obj1 = "hello"; String obj2 = "hello"; String obj3 = "hello"; Here we are declaring three String reference variables and in heap one obj...

Every java program has at least three class loaders. - The bootstrap class loader - The extension class loader. - The system class loader. The bootstrap class loader loads the system classes from the JAR Fle rt.jar(part of JRE System Library) . It is an integral part of the virtual machine and is usually implemented in C. There is no Class loader object corresponding to the bootstrap class loader. For example. String.class.getClassLoade r() will return null since String class is loader by bootstrap loader. The extension class loaders loads "standard extensions "from the jre/lib/ext directory. The system class loader loads the application classes. It locates the classes in the directories and JAR/ZIP files on the class path. The System class loader also called application class loader. In Sun's java implementation , the extension adn system class loaders are implemented in java. Both are instances of URLClass loader. You can just go through the source code of URLCla...