ClassNotFoundException vs NoClassDefFoundError

	ClassNotFoundException	NoClassDefFoundError
Exception or Error?	It is of type java.lang.Exception.It is a Checked Exception.	It is of type java.lang.Error.
When it occurs?Explicit loading or Implicit loading?	It occurs when an application tries to load a class at run time which is not found in the classpath. Table of Contents Toggle Explicit loading:It is thrown when the code is directly trying to load a class, passing the String argument representing a Fully Qualified Name of the class. e.g. Class.forName(String), or ClassLoader.loadClass(String).	It occurs when java runtime system doesn’t find a class definition, which is present at compile time, but missing at run time. Implicit loading:It is thrown when the JVM is asked to load a class indirectly. e.g. when class A is using class B and class B is not on classpath, NoClassDefFoundError will be thrown.
Situations in which these are thrown?	It occurs if we try to load a class at run-time using with Class.forName() or ClassLoader.loadClass() or ClassLoader.findSystemClass() method and requested class is not available.	When JVM tries to load in the definition of a class (as part of a normal method call or as part of creating a new instance using the new expression) and no definition of the class could be found (bad format of the class, the version number of a class not matching, etc.). Class can’t be loaded on the following reasons: failure to load the dependent class; the dependent class has a bad format; the version number of the class is incorrect; the class been loaded already in a different classloader;exception from static block etc.
Thrown by?	It is thrown by the application itself.	It is thrown by the JVM.
Irrecoverable or Recoverable?	Irrecoverable:NoClassDefFoundError refers irrecoverable situation that are not being handled by try/catch/finally block.	Recoverable:ClassNotFoundException is checked exception, which requires handling using try/catch/finally block.

Example

ClassNotFoundException

package com.test;

public class TestClass {

public static void main(String[] args) throws ClassNotFoundException {
Class.forName(“com.test.TestClass1”);
}

}

Output

NoClassDefFoundError

Example1: Exception in static block

package com.test;

public class TestClass {

static{
int i=10/0;//Arithmetic Exception
}

public static void main(String[] args) throws ClassNotFoundException {
TestClass testclass = new TestClass();
}

}

 

 

 

Example2:

On deleting the .class file after successful compilation. It will throw NoClassDefFoundError.

package com.test;

public class TestClass {

public static void main(String[] args) throws ClassNotFoundException {

TestClass testclass = new TestClass();

}

}