If you ever use Eclipse trying to debug into Java’s system APIs, such as java.lang.String or java.math.BigInteger, you may find that even you can step over or step in, or have the correct source file open and the correct line of codes highlighted, you still could not see the local variables’ value and method’s parameters are shown in pattern of “arg0”, “arg1” and so on.
Yes, you are already using JDK instead of JRE. But you still have the above problem. What’s wrong? It’s not a bug of Eclipse. It is all about the rt.jar along with the JDK (1.5 or 1.6). In Sun’s official JDK release, debug symbols are already packed into the rt.jar. But local variables’ debug information is not packed. Sun may consider that it is not OK to includes those local variables’ debugging information. That is the source of problem.
To solve this problem, you may need to upgrade to JDK 1.6. Download DEBUG jar file from
Double click it to install a new JDK. And configure your Eclipse to use the new JDK.
For JDK 1.5, recompiling rt.jar by yourself, or other information, please visit
for a detailed discussion.