2 class in 1 file ?

Question

How can I get classes names from a java file. like
A.java
public class B {
class C {
java ClassChecker A.java
B
Cthank u.

Answer 1

As BIJ001 mentioned, if you actually compile A.java you'll end up with an A.class and a B.class.
If you really want some program you can run which analyzes the source file... well, you need a program which analyzes the source file. This is actually a pretty complicated problem.
If you're looking for simple solutions, you might try running the java compiler and seeing what comes out. That's kind of hackish though. What you really want is some sort of customized Java parser. Use something like ANTLR (http://www.antlr.org/) to generate a language recognizer that parses the .java file and extract the names of all the classes within.
This is actually easier than it first sounds. There are several grammar files available on ATNLR's website for the Java language. If we pick one like this:
http://www.antlr.org/grammar/1090713067533/index.html
then make some minor modifications to the ClassDefinition clause to print out the class's identifier as we parse the class:
// Definition of a Java class
classDefinition![AST modifiers]
     :     "class" id:IDENT  {System.out.println(id.getText());}
          // it _might_ have type paramaters
          (tp:typeParameters)?
          // it _might_ have a superclass...
          sc:superClassClause
          // it might implement some interfaces...
          ic:implementsClause
          // now parse the body of the class
          cb:classBlock
          {#classDefinition = #(#[CLASS_DEF,"CLASS_DEF"],
                                        modifiers,id,tp,sc,ic,cb);}
     ;then we just need to run the grammar file through ANTLR and we have exactly what you're looking for. (This is also actually a little hackish; purists would tell you to build an abstract syntax tree and then walk the syntax tree looking for class definitions. That would be a more flexible solution, depending on what you intend to do.)
Here; here's a netbeans project that does it all:
http://www.thedreaming.org/~quartz/JavaParser.zip
To recompile, install ANTLR (I was using 2.7.5), then go to the "antlr" directory in that zip file and edit and run "rebuild.cmd" to rebuild the grammar files. Then, load the project into netbeans, add the antlr library, and run. Or, if you just want to try it out, go to the dist directory and run:
java -jar JavaParser.jar ..\src\A.java
Hope that helps!