I have some .class files that I need to convert to .java so I did:
javap -c ClassName.class
and all the time I have the same error
javap to read the bytecodeThe javap command takes class-names without the .class extension. Try
javap -c ClassName
javap will however not give you the implementations of the methods in java-syntax. It will at most give it to you in JVM bytecode format.
To actually decompile (i.e., do the reverse of javac) you will have to use proper decompiler. See for instance the following related question: