jdb has a default class filter for filtering out JDK library classes. This allows you to single step into a library call, and not have the single step complete until you are back in user code. This default class filter can be displayed and set using the jdb "exclude" command:

> exclude
java.*,javax.*,sun.*,com.sun.*,

The jdb Env.java file is where this default is setup:

    static private List<String> excludes() {
        if (excludes == null) {
            setExcludes("java.*, javax.*, sun.*, com.sun.*");
        }
        return excludes;
    }

JDK 9 added jdk.internal.*, and these classes currently do not get filtered by default. jdk.* should be added to the default filter to capture the jdk.internal package, an any others that fall under jdk.*.