5 Examples of Enhanced for loop in Java.How to join two threads in Java? Thread.join() exa.How to recursive copy directory in Java with sub-d.Difference between Daemon Thread vs User Thread in.Can you join two unrelated tables in SQL? Cross Jo.How to Convert a List of String to Comma Separated. ![]() How to combine two Map in Java? Example Tutorial.The Ultimate Guide of String in Java - Examples.Difference between OCAJP and OCPJP Certification E.5 ways to redirect a web page using JavaScript and.10 Example of jQuery Selectors for Beginners.Difference between OCAJP7, OCAJP8, and OCAJP11 Cer.3 ways to create random numbers in a range in Java.Difference between Type 1, 2, 3 and 4 JDBC Driver.How to Create Java Project with Maven in Eclipse.How to Implement Thread-Safe Bounded Buffer in Jav.To start with, you can read Java Puzzlers by Joshua Bloch. To deal with, two most important things, is knowledge of Classpath and ClassLoader in Java. Most of the time, it's just a missing JAR file that causes this problem, but sometimes it can be a nightmare to solve, like in case your application is picking classpath from the manifest file, and you are checking classpath entry somewhere else. That's all on NoClassDefFoundError in Java and the common reason which causes Exceptions in thread "main" in Java. That is the root cause of the NoClassDefFoundError you were seeing. So next time, if you see the NoClassDefFound error in your Java application, make sure you search for static initializer error, i.e., in your log file. In that case, when class B will be loaded, it will throw "Exception in thread "main" " because it will not be able to find it's a dependency which is class A. I suppose class A throws Exception from the static initializer block, and class B uses class A. This is the block of code that is declared using static keywords and executed when a class is loaded. One of the most common reasons for "Exception in thread "main" " is the error in the static initializer block. See here to learn more about how to add multiple JAR files in the classpath. Instead, you should define the classpath with a list of JAR files in the start script and start your Java application using the java -classpath command. For example, in Java classloader works by delegation and visibility. Sometimes in complex environments, e.g., Java EE container, the offender cases may be available in classpath but not visible to the classLoader trying to load that particular class. Due to the Visibility issues between multiple Classloaders See here to learn more useful Eclipse shortcuts for Java developers.Ģ. In Eclipse, you can use shortcuts like search resource (Ctrl + R) or search type (Ctrl + T) to find which JAR file that particular class belongs to and then check if that JAR is available in the classpath or not. In short, the first step to solving "Exception in thread "main" " is to check if the offender class is available in classpath or not. ![]() Similarly, you might have seen : org/apache/xmlbeans/XmlObject which comes if you are using XMLbeans but xmlbeans-2.60.jar is not present in your classpath (see here).Īnother common one is : org/dom4j/DocumentException, which comes due to missing dom4j.jar file (see here). See here to learn more about troubleshooting this particular issue. As soon as you add that JAR into the classpath, the error goes away. The simplest reasons for this error are the missing log4j.jar file in the classpath. If the static initializer block of a class throws an Exception during loading, the class will not be available for others to use. On the other hand, NoClassDefFoundError comes when the class was available at compile time but somehow not available at runtime. For example, when you load JDBC driver using Class.forName(String classname), you will get j instead of NoClassDefFoundError. The ClassNotFoundException comes when Java tries to load a class by its binary name during runtime, and Class is not available at that time. N oClassDefFoundError in Java is also related to class loading in Java but there is a slight difference between NoClassDefFoundError and ClassNotFoundException in Java. Java Programmers often confuse between java.lang. This could be due to a missing JAR file, any permission issue, or an incorrect classpath on runtime, depending upon your environment. It's denoted by j and comes when that particular class is present during compile time but somehow not available during runtime.
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