How to resolve java.lang.NoClassDefFoundError in Java

Question

I was trying to compile my SPM-project then message displayed saying "Low memory". So my netbeans(8.0) projects are saved inside Documents,NetBeans Projects Folder.So i removed some unwanted Projects there.After that I tried to compile my project then this error message was displayed ,Please Give me a help to resolve this problem.The whole error message is shown below,

java.lang.NoClassDefFoundError: spm_project/Nonacademic
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
    at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
    at java.lang.Class.getMethod0(Class.java:3018)
    at java.lang.Class.getMethod(Class.java:1784)
    at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)   at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
    at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)
Caused by: java.lang.ClassNotFoundException: spm_project.Nonacademic
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 7 more
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" Java Result: 1
BUILD SUCCESSFUL (total time: 1 second)

Answer 1

Important to Keep Some Point Regarding this Error :

1. This is caused when there is a class file that your code depends on and it is present at compile time but not found at runtime. Look for differences in your build time and runtime classpaths.
2. This exception indicates that the class was not found on the classpath. This indicates that we were trying to load the class definition, and the class did not exist on the classpath.