Java类动态加载过程

Question

I am having an argument with my professor which I cant seem to find an answer to in google... My question is, when I use a method that is in another class, the JVM will try and find the class's .class file right? and the argument is this: if the .class file is not found will there be a search for the source file and if found it will be recompiled or will it throw an exception? Thanks!

UPDATE: I rephrased the question, I will be very grateful for your help!

Answer 1

It is not at all the standard behavior, and will not work in a normal environment.

However, I have heard of some commercial app server distributions that were able to do that... someone told me about older weblogic versions, configured in development mode, but maybe just an urban legend :P

I guess that you could write a tuned classloader that looked for .java files in the classpath and, given it runs on a JDK with a java compiler, do what you say.

Answer 2

The standard JRE does not even include a compiler for Java source code. To compile Java source code you need a JDK or an IDE which includes its own Java compiler. If you compile your source code using javac or the IDE's built-in compiler, these compilers will search for source files of the referenced classes and compile them if the .class file was not found or if the source file is newer than the class file. But if you, eg delete the class file of the referenced class afterwards and run your program, the JVM won't search for a source file. It will throw an NoClassDefFoundError .

Answer 3

JVM will not search for source file for the class whose method we are trying to invoke. JVM will throw a exception like:

    Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
    Employee cannot be resolved to a type
    Employee cannot be resolved to a type
    at com.test.TestIt.main(TestIt.java:7)

Employee is the class whose method we want to call(.class file is not created for Employee)