When do we use Static and Dynamic class Loading?

Question

I know the difference between Static class loading and Dynamic class loading. In general,we always use Static class loading only.Can anyone tell, under which situations we use Dynamic class loading??

Answer 1

Dynamic Class Loading allows the loading of java code that is not known about before a program starts. The Java model loads classes as needed and need not know the name of all classes in a collection before any one of its classes can be loaded and run.

For example : Depending on user input you want to create only one object and there are hundreds of classes. Then you don't need load all classes. You can create object at run time by dynamic class loading.

Code:

try {
    InputStreamReader in = new InputStreamReader(System.in);
    BufferedReader reader = new BufferedReader(in);

    System.out.println("Enter Class Name: ");
    String whatClass = reader.readLine();

    Class exampleClass = Class.forName(whatClass);
    Object ob = exampleClass.newInstance();

} catch (ClassNotFoundException e) {
    e.printStackTrace();

} catch (Exception e) {
    e.printStackTrace();
}

Answer 2

DYNAMIC CLASS LOADING

It allows you to build your applications so that key external dependencies are not compiled into the application source-code.

APPLICATIONS

JDBC

For example, in the JDBC case, it allows you to switch between different driver implementations, and (in theory) different database vendors without changing your source code.

PLUG-INS

Another use-case is when some supplier develops a generic form of an application with extension points that allow customers to "plug in" their own custom classes. The custom classes are typically loaded using Class.forName(...).

FRAMEWORKS AND CONTAINERS

A third use-case is application frameworks and containers which typically use Class.forName(...) under the hood to dynamically load the classes for application-specific beans, servlets, and so on.

OTHERS

A fourth use-case is where the application (or more likely an application library) has modules that are not used in a typical application run. By using Class.forName(...) internally, the application or library can avoid the CPU and memory overhead of loading and initializing large numbers of unwanted classes. (The Sun Swing libraries apparently do this to reduce application startup times, and I'm sure there are other examples.)

Refer Dynamic Class Loading