How the class loader works

In this example we shall show you how the class loader works. To see how the class loader works we have performed the following steps:

  • We have created three classes, A, B and C, that each one uses a static block to print a message. The code in a static block is executed when the class is loaded by the class loader.
  • We create a new instance of A class, then we get an object of B class, using the forName(String className) API method of Class and then we create a new C object and see the printed messages from the static blocks,

as described in the code snippet below.  

package com.javacodegeeks.snippets.core;

class A {

    static {

  System.out.println("Loading A");

class B {

    static {

  System.out.println("Loading B");

class C {

    static {

  System.out.println("Loading C");

public class ClassLoader {

    public static void main(String[] args) {


  System.out.println("inside main");

  new A();

  System.out.println("inside main : After creating A");

  try {


  } catch (ClassNotFoundException e) {

System.out.println("inside main : Couldn't find B");


  System.out.println("inside main : After Class.forName("B")");

  new C();

  System.out.println("inside main : After creating C");



inside main
Loading A
inside main : After creating A
inside main : Couldn't find B
inside main : After Class.forName("B")
Loading C
inside main : After creating C

This was an example of how the class loader works in Java.

Byron Kiourtzoglou

Byron is a master software engineer working in the IT and Telecom domains. He is an applications developer in a wide variety of applications/services. He is currently acting as the team leader and technical architect for a proprietary service creation and integration platform for both the IT and Telecom industries in addition to a in-house big data real-time analytics solution. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.
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