Causes of ClassNotFoundException in Java

To load a class, java.lang.ClassNotFoundException uses 3 methods:

• Class.forName(): Used to load the JDBC Driver
• ClassLoader.findSystemClass(): Used to load the class through SystemClass loader.
• ClassLoader.loadClass(): Used to load the class

From the above image, we can see that many jar files are present. They are absolutely necessary if the java code wants to interact with MySQL, MongoDB, etc., kind of databases, and also few functionalities need these jar files to be present in the build path. If they are not added, first editors show the errors themselves and provide the option of corrections too.

In Java, java.lang.ClassNotFoundException is a checked exception and occurs when the Java Virtual Machine (JVM) tries to load a particular class and the specified class cannot be found in the classpath. ClassNotFoundException should be handled with a try-catch block or using the throw keyword.

In older days, there are no editors like Eclipse are available. Even in Notepad, people have done Java coding by using the “javac” command to compile the Java files, and they will create a ‘.class’ file. Sometimes accidentally the generated class files might be lost or set in different locations and hence there are a lot of chances of ClassNotFoundException occurring. After the existence of editors like Eclipse, Netbeans, etc., IDE creates a ClassPath file kind of entry.