src/main/java/org/plumelib/bcelutil/BcelUtil.java
public static boolean inJdk(@ClassGetName String classname) {
    return classname.startsWith("java.")
        || classname.startsWith("com.oracle.")
        || classname.startsWith("com.sun.")
        || classname.startsWith("javax.")
        || classname.startsWith("jdk.")
        || classname.startsWith("org.ietf.")
        || 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 inJdk(@ClassGetName String classname) {
    return classname.startsWith("java.")
        || classname.startsWith("com.oracle.")
        || classname.startsWith("com.sun.")
        || classname.startsWith("javax.")
        || classname.startsWith("jdk.")
        || classname.startsWith("org.ietf.")
        || 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 the format of Class.getName(); the class should not be
an array
@return true iff the class is in a package that is in the JDK (rt.jar)