java - Add a new class to an existing JAR File(which contains source code) -

i'll try illustrate problem simple can.

i have jar file, extracted using winrar. (the jar file contains open source android library).
want modify jar file adding new class library.

so here steps:
first, created class using eclipse , set package name same android's library package name.
second, copied java file folder of other java files in library.
third, tried compile java file via cmd using javac.

the path of new java file , other .java , .class files of library is: c:\com\example\core\
name of new java file be: "mynewclass.java"
command run via cmd is: javac c:\com\example\core\mynewclass.java

but, during compilation many errors saying: cannot find symbols.

i've been looking solution of problem couldn't figure how solve , make new jar file having class created seperately.

what missing?

as per earlier comments:

rather trying modify jar, can access full source code of universal image loader library cloning repository using git or hitting "download zip" on righthand side of page linked.

once have source, import library in ide. there on you'll able build whole thing scratch, make adjustments/modifications like, etc.