NoClassDefFoundError and classnotfoundexception exceptions

1. brief introduction ClassNotFoundException and NoClassDefFoundError When JVM Unable to find classpath The requested class occurred .

2.ClassNotFoundException ClassNotFoundException It's a checked exception , An exception that occurs when an application attempts to load a class with its fully qualified name and cannot find it on the classpath . Mainly occurs when trying to use Class.forName()、ClassLoader.loadClass()、ClassLoader.findSystemClass() When loading a class . for example ： Load a class that doesn't exist

Class.forName("acb.s.sad")

3.NoClassDefFoundError Happen when NoClassDefFoundError ( java  fhadmin.cn), The system does not work properly , And it can't be recovered . When JVM Try the following ：

Use new Instantiate a class Use method calls to load classes When the compiler can successfully compile classes , but java The runtime cannot find the class file , Errors will occur . It usually occurs when an exception occurs when executing a static block or initializing a static field of a class , So class initialization failed 4. Solution The main reason is that the runtime class file （ Class path ） Unavailable . resolvent ：

Ensure that the class containing the class or... Can be used in the classpath jar. without , You need to add it manually . If available on the classpath , Then it is possible that the path is covered . At this time, you need to find the exact path of the class . 5. summary ClassNotFoundException and NoClassDefFoundError It's all because of java The runtime could not find the class related . ClassNotFoundException yes java Exception thrown when loading class at runtime (Exception), And the name is provided at run time . NoClassDefFoundError Is that this class exists at compile time , but java The runtime cannot find... On the path .