src/main/java/org/plumelib/bcelutil/BcelUtil.java
public static boolean inJdkInternalform(@InternalForm String classname) {
    return classname.startsWith("java/")
        || classname.startsWith("com/oracle/")
        || classname.startsWith("com/sun/")
        || classname.startsWith("javax/")
        || classname.startsWith("jdk/")
        || classname.startsWith("org/ietj/")
        || classname.startsWith("org/jcp/")
        || classname.startsWith("org/omg/")
        || classname.startsWith("org/w3c/")
        || classname.startsWith("org/xml/")
        || classname.startsWith("sun/")
        || classname.startsWith("sunw/");
  }
public static boolean inJdkInternalform(@InternalForm String classname) {
    return classname.startsWith("java/")
        || classname.startsWith("com/oracle/")
        || classname.startsWith("com/sun/")
        || classname.startsWith("javax/")
        || classname.startsWith("jdk/")
        || classname.startsWith("org/ietj/")
        || classname.startsWith("org/jcp/")
        || classname.startsWith("org/omg/")
        || classname.startsWith("org/w3c/")
        || classname.startsWith("org/xml/")
        || classname.startsWith("sun/")
        || classname.startsWith("sunw/");
  }
Returns whether or not the class is part of the JDK (rt.jar).

@param classname the class to test, in internal form
@return true iff the class is part of the JDK (rt.jar)