Flow of class loading for a simple program

by

You will run your Sample class as follows

> java Sample

for little magic, check out the output of-verbose:class option and you see tons of following lines..

[Opened C:\jdk1.6.0_14\jre\lib\rt.jar]
[Loaded java.lang.Object from C:\jdk1.6.0_14\jre\lib\rt.jar]
[Loaded java.io.Serializable from C:\jdk1.6.0_14\jre\lib\rt.jar]
[Loaded java.lang.Comparable from C:\jdk1.6.0_14\jre\lib\rt.jar]
.
.
.
.
.
.
[Loaded java.security.cert.Certificate from C:\jdk1.6.0_14\jre\lib\rt.jar]
[Loaded Sample from file:/D:/tmp/]
[Loaded java.lang.Shutdown from C:\jdk1.6.0_14\jre\lib\rt.jar]
[Loaded java.lang.Shutdown$Lock from C:\jdk1.6.0_14\jre\lib\rt.jar]

You see a bunch of classes from \jre\lib\rt.jar are loaded, much before your class is loaded by Bootstrap class loader (or Primordial ). These are the pre-requisite for running any Java program hence loaded by Bootstrap.

Another set of jars is loaded by Extension class loader. In this particular example, there was no need of any classes from the lib \jre\lib\ext hence its not loaded. But Extension class loader are specifically assigned the task of loading the classes from the extension lib.

EDIT: Apart from the standard platform java classes Sun/Oracle also provide a set of jars which are used to extend the platform’s core API. The jars placed in the extension lib folder are automatically placed in the classpath and hence not needed to be included in classpath explicitly. Here is nice official article on the same topic.

Finally, your class Sample is loaded by Application class loader after Bootstrap and Extension have finished loading.

More Related Contents:

  1. What is the difference between Class.getResource() and ClassLoader.getResource()?
  2. Java, Classpath, Classloading => Multiple Versions of the same jar/project
  3. How to load a jar file at runtime [duplicate]
  4. Java resource as File
  5. URL to load resources from the classpath in Java
  6. Dealing with “Xerces hell” in Java/Maven?
  7. Difference between thread’s context class loader and normal classloader
  8. Determine which JAR file a class is from
  9. What does JVM flag CMSClassUnloadingEnabled actually do?
  10. Singleton class with several different classloaders
  11. How to load a Java class dynamically on android/dalvik?
  12. Java – how to load different versions of the same class?
  13. When is the static block of a class executed?
  14. Load properties file in JAR?
  15. How can I list all classes loaded in a specific class loader
  16. In Java, is it possible to know whether a class has already been loaded?
  17. How to access resource using class loader in Java 9
  18. Class.forName() vs ClassLoader.loadClass() – which to use for dynamic loading? [duplicate]
  19. Preloading java classes/libraries at jar startup?
  20. Java verbose class loading
  21. Replacement System Classloader for Classes In Jars containing Jars
  22. ClassCastException because of classloaders?
  23. What is a Java ClassLoader?
  24. How to deal with LinkageErrors in Java?
  25. CompletableFuture / ForkJoinPool Set Class Loader
  26. Check if class exists in Java classpath without running its static initializer?
  27. ClassLoader getResourceAsStream returns null
  28. Static references are cleared–does Android unload classes at runtime if unused?
  29. How to replace classes in a running application in java ?
  30. Java : in what order are static final fields initialized?

Leave a Comment