How is this Java project using the language reserved words as identifiers?

Question

I have de-compiled a Java project using JD-GUI, and was surprised when I saw that all identifiers are using Java reserved keywords such as int do throw extends etc..

Here is a snippet of the project:

public class try extends Thread {
  private int do;
  
  private JSONArray if;
  
  private int for;
  
  private String int;
  
  private String new;
}

I read on a another post about using when UTF-16 encoding, some characters might look the same, but are actually different, so I switched the encoding using Notepad++ but that had no effect on the display.

I also tried using a few de-obfuscators from Github, but no success.

I know that it is not really using the reserved keywords, but i can't figure it out, so what's the trick here?

EDIT:

Here is the smallest class in the project:

package tech.iresponse.break;

import org.apache.commons.lang.exception.ExceptionUtils;
import org.apache.log4j.Logger;

public class do {
  public static void do(Throwable paramThrowable) {
    Logger.getLogger("rootLogger").error(ExceptionUtils.getFullStackTrace(paramThrowable));
  }
}


/* Location:              C:\Users\User\Desktop\app.jar!\tech\iresponse\break\do.class
 * Java compiler version: 8 (52.0)
 * JD-Core Version:       1.1.3
 */

And here is the hexdump:

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00001490

Answer 1

While reserved words may not occur in Java source code, they are permitted in compiled Java code. Some code obfuscation tools can make use of this to make decompiling harder. For instance, ProGuard provides the following option:

-obfuscationdictionary filename

Specifies a text file from which all valid words are used as obfuscated field and method names. By default, short names like 'a', 'b', etc. are used as obfuscated names. With an obfuscation dictionary, you can specify a list of reserved key words, or identifiers with foreign characters, for instance. White space, punctuation characters, duplicate words, and comments after a# sign are ignored. Note that an obfuscation dictionary hardly improves the obfuscation. Decent compilers can automatically replace them, and the effect can fairly simply be undone by obfuscating again with simpler names. The most useful application is specifying strings that are typically already present in class files (such as 'Code'), thus reducing the class file sizes just a little bit more. Only applicable when obfuscating.

So if you feed this a list with Java identifiers (such as this one) you end up with a class file that causes syntax errors if decompiled. Of course, you can simply rename the variables to fix these compilation errors (for instance by using ProGuard yourself before decompiling), so this is only a minor inconvenience.