Skip to main content

What causes and what are the differences between NoClassDefFoundError and ClassNotFoundException?

The difference from the Java API Specifications is as follows.
Thrown when an application tries to load in a class through its string name using:
  • The forName method in class Class.
  • The findSystemClass method in class ClassLoader.
  • The loadClass method in class ClassLoader.
but no definition for the class with the specified name could be found.
This exception also occurs when you have two class loaders and if a ClassLoader tries to access a class which is loaded by another classloader in Java. You must be wondering that what actually is classloader in Java. Java ClassLoader is a part of Java Runtime Environment that dynamically loads Java classes in JVM(Java Virtual Machine). The Java Runtime System does not need to know about files and files system because of classloaders.


For NoClassDefFoundError:
Thrown if the Java Virtual Machine or a ClassLoader instance 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.
The searched-for class definition existed when the currently executing class was compiled, but the definition can no longer be found.
NoClassDefFoundError occurs when class was present during compile time and program was compiled and linked successfully but class was not present during runtime. It is error which is derived from LinkageError. Linkage error occurs when a class has some dependencies on another class and latter class changes after compilation of former class. NoClassFoundError is the result of implicit loading of class because of calling a method or accessing a variable from that class. This error is more difficult to debug and find the reason why this error occurred. So in this case you should always check the classes which are dependent on this class.
ClassNotFoundException
NoClassDefFoundError
It is an exception. It is of type java.lang.Exception.
It is an error. It is of type java.lang.Error.
It occurs when an application tries to load a class at run time which is not updated in the classpath.
It occurs when java runtime system doesn’t find a class definition, which is present at compile time, but missing at run time.
It is thrown by the application itself. It is thrown by the methods like Class.forName(), loadClass() and findSystemClass().
It is thrown by the Java Runtime System.
It occurs when classpath is not updated with required JAR files.
It occurs when required class definition is missing at runtime.

ClassNotFoundExceptionNoClassDefFoundError
It is an exception. It is of type java.lang.Exception.It is an error. It is of type java.lang.Error.
It occurs when an application tries to load a class at run time which is not updated in the classpath.It occurs when java runtime system doesn’t find a class definition, which is present at compile time, but missing at run time.
It is thrown by the application itself. It is thrown by the methods like Class.forName(), loadClass() and findSystemClass().It is thrown by the Java Runtime System.
It occurs when classpath is not updated with required JAR files.It occurs when required class definition is missing at run time

Comments

Post a Comment

Popular posts from this blog

Yahoo! Calendar "Add Event" Seed URL Parameters

I can't seem to find any official documentation on this, so here are my notes. Some information gathered from  http://richmarr.wordpress.com/tag/calendar/ Other information gathered through trial and error, and close examination of the "Add Event" form on Yahoo!'s site. Yahoo! Calendar URL Parameters Parameter Required Example Value Notes v Required 60 Must be  60 . Possibly a version number? TITLE Required Event title Line feeds will appear in the confirmation screen, but will not be saved. May not contain HTML. ST Required 20090514T180000Z Event start time in UTC. Will be converted to the user's time zone. 20090514T180000 Event start time in user's local time 20090514 Event start time for an all day event. DUR value is ignored if this form is used. DUR 0200 Duration of the event. Format is HHMM, zero-padded. MM may range up to 99, and is converted into hours appropriately. HH values over 24 hours appear to be modulated by 24. Durations t...
1 comment
Read more

HTML5 30-Day Course Outline

  🗓️ Week 1: HTML5 Fundamentals and Structure 🎯 Goal: Understand the structure of HTML5 and core elements. Day 1: Introduction to HTML5 ✅ Concepts What is HTML5 and its role in web development <!DOCTYPE html> declaration Basic HTML structure ( <html> , <head> , <body> ) Character encoding ( UTF-8 ) ✅ Example Code html <!DOCTYPE html > < html lang = "en" > < head > < meta charset = "UTF-8" > < title >My First HTML5 Page </ title > </ head > < body > < h1 >Hello World! </ h1 > </ body > </ html > ✅ Task: 👉 Create a basic HTML page with a title and h1 element. Day 2: HTML Elements and Semantics ✅ Concepts Block vs Inline Elements <div> , <span> , <article> , <section> , <aside> , <main> , <footer> Importance of semantic HTML for SEO ✅ Example Code html < article > < header > ...
Post a Comment
Read more

Java KeyWords

Java Keywords Some identifiers are reserved in Java which has separate functionality and meaning such type of reserved identifiers are called reserved words. Java has 54 reserved keywords. We can divide them into the following categories. Primitive types and void : 9 keywords boolean : creates a boolean variable. The only possible values are true and false and the default value is false. byte : creates a byte variable. A byte takes 8-bits and ranges from -128 to 127. char : used to create a character variable. It takes 2-bytes and it’s unsigned. The value ranges from 0 to 65,536. short : create a short variable of 2-bytes. The value ranges from -32,768 to 32,767. int : create an integer variable, takes 4-bytes and the range is from -2,147,483,648 to 2,147,483,647 long : creates a long variable, takes 8-bytes and the range is from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807. float : creates a signed floating point variable using 4-bytes. double ...
Post a Comment
Read more