Why in Java, we get ClassNotFoundException when the class exists?

Whenever we try to load a class, if the class loader cannot find the class at the specified path, a ClassNotFoundException will be generated.

This may happen when executing a java program, using the forName() method of the class named Class or the loadClass()## of the ClassLoader class # Method to explicitly load the class. These two classes accept a string value representing the class name and load the specified class.

When passing class names to these methods, you need to ensure that -

The class names passed to these methods should be accurate.
• The specified class (along with the package) should be located in the current directory or its path should be listed in the environment variable classpath.

Example

Suppose we create a file named

Sample in the directory D:// and compile as follows -

package myPackage.example;
public class Sample {
   static {
      System.out.println("The class named Sample loaded successfully.........");
   }
}

Compile

D:\>javac -d . Sample.java

This will create a package in the current directory myPackage.example and build ## in it

.class file of the #Sample class. So when loading this class you need to put it in the same directory and pass the absolute class name to Class.forName() or loadClass()Example p>

Live Demonstration

public class ClassNotFoundExample {
   public static void main(String args[]) {
      try {
         Class.forName("myPackage.exampl.Sample");
      }catch (ClassNotFoundException ex) {
         ex.printStackTrace();
      }
   }
}

Exception

While executing the above program, you will get the following exception due to the misspelling of the name of the package.

D:\>java ClassNotFoundExample
java.lang.ClassNotFoundException: myPackage.exampl.Sample
   at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(Unknown Source)
   at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(Unknown Source)
   at java.base/java.lang.ClassLoader.loadClass(Unknown Source)
   at java.base/java.lang.Class.forName0(Native Method)
   at java.base/java.lang.Class.forName(Unknown Source)
   at ClassNotFoundExample.main(ClassNotFoundExample.java:4)

If you are trying to access a specific class from another directory, you need to set the classpath -

A folder containing the following content (the outermost package) .class document.

• Or,

The jar file containing the class.
Assume we have corrected the spelling problem and try to load the class from a Java file in the E:// directory

Example

Live demonstration

public class ClassNotFoundExample {
   public static void main(String args[]) {
      try {
         Class.forName("myPackage.example.Sample");
      }catch (ClassNotFoundException ex) {
         ex.printStackTrace();
      }
   }
}

Exception

You will still encounter the same exception because the package containing the .class file for the specified class (or the jar file containing it) is neither in the current directory nor in the path list environment variable classpath.

E:\>java ClassNotFoundExample
java.lang.ClassNotFoundException: myPackage.example.Sample
   at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(Unknown Source)
   at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(Unknown Source)
   at java.base/java.lang.ClassLoader.loadClass(Unknown Source)
   at java.base/java.lang.Class.forName0(Native Method)
   at java.base/java.lang.Class.forName(Unknown Source)
   at ClassNotFoundExample.main(ClassNotFoundExample.java:4)

In the current scenario, set the classpath to the directory containing the package of the required class, i.e. "

D://

" and execute the above java program to make it work.

E:\>javac ClassNotFoundExample.java
E:\>java ClassNotFoundExample
The class named Sample loaded successfully.........

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