Jdec sometimes generates class names matching jcoder keywords or constant values, for example:

$ cat Method.java I.java z.java
// JcodTokens.ConstType.CONSTANT_METHOD
class Method {}

// Tables.StackMapType.ITEM_Integer
interface I {}

// JcodTokens.Token.ZEROINDEX
class z {}

$ javac Method.java I.java z.java
$ java -jar asmtools.jar jdec Method.class > Method.jcod
$ java -jar asmtools.jar jcoder Method.jcod
org.openjdk.asmtools.jcoder.SyntaxError
    [...]
Method.jcod:1: Name expected.
class Method {
     ^
1 error

$ java -jar asmtools.jar jdec I.class > I.jcod
$ java -jar asmtools.jar jcoder I.jcod
org.openjdk.asmtools.jcoder.SyntaxError
    [...]
I.jcod:1: Name expected.
class I {
     ^
1 error

$ java -jar asmtools.jar jdec z.class > z.jcod
$ java -jar asmtools.jar jcoder z.jcod
org.openjdk.asmtools.jcoder.SyntaxError
    [...]
z.jcod:1: Name expected.
class z {
     ^
1 error

A possible fix (in ClassData.decodeClass()) would be to make jdec print the file name instead of the class name when the latter matches a jcoder keyword or constant value.