Is there any method which reflects the names of classes of java?

Question

is there any method with which dynamically we can get all the packages's name along with their classes of java(specially core classes of java)?if not how can we do that?

Answer 1

The resource from which the Java VM loads the classes is considered to be implementation dependent. It may be class files or jar files contained in a file system hierarchy, or some kind of remote database. The now defunct Microsoft VM used a database repository that was able to reside on a remote class server within a network domain.
Unfortunately, Sun did not design a class resource service interface with a "list resources" function, only a "get resource" function. You can get the class resource for any named class, but you cannot list packages or classes within a package or at the root level.
This is further complicated by the fact that there is no such thing as an "installed package" as Java does not define any package installation system. The packages available to any runtime instance of the JVM is defined by the classpath properties passed from the OS. Different JVM instances can have completely different sets of available packages because they were passed different classpath values by the OS.
If you know the class resource of the runtime environment, then you could create a subclass of the sun.misc.URLClassPath class and add to it methods that will list packages and classes found within a package using the interface of that known class resource.
Most runtime environments use a standard hierarchical file system to hold jar and class files. A subclass of sun.misc.URLClassPath could use the java.io.File class to traverse the file system classpath paths in search of package directories and class files (Watch out for recursive directory links).
The root packages can be obtained from the three levels of classpath paths in the System properties used by the JVM:     "sun.boot.class.path"
     "java.ext.dirs"
     "java.class.path"The collection of file system paths obtained from these properties would be searched for the names of the root level package directory names. Just remember that this will only work in a runtime environment that only uses this kind of class resource. If you run this where some other resource is also used, you will not see all of the packages available to that JVM.
One note of caution: A single directory can hold package directories, jar files, and class files that belong to a specific package, but the package may include other package directories, jar files, and class files that are contained in other directories. Pieces of a single package may be strewn throughout the file system. The only way to find them all is to scan all of the classpath paths for that same package name. The directory does not define the package, it only provides more content for that package.
I hope you find this of some use.