Explain the difference of isValid, isActive, isUsable

    }

    /**

     * Checks if the supplied subscription ID is valid.

     * Note: a valid subscription ID does not necessarily correspond to an active subscription.

     * Check if the supplied subscription ID is valid.

     *

     * <p>A valid subscription ID is not necessarily an active subscription ID

     * (see {@link #isActiveSubscriptionId(int)}) or an usable subscription ID

     * (see {@link #isUsableSubscriptionId(int)}). Unless specifically noted, subscription

     * APIs work with a valid subscription ID.

     *

     * @param subscriptionId The subscription ID.

     * @return true if the supplied subscriptionId is valid; false otherwise.

     * @return {@code true} if the supplied subscriptionId is valid; {@code false} otherwise.

     */

    public static boolean isValidSubscriptionId(int subscriptionId) {

        return subscriptionId > INVALID_SUBSCRIPTION_ID;

    }

    /**

     * Check if the subscription ID is usable.

     * Check if the supplied subscription ID is usable.

     *

     * A usable subscription ID has a valid value except some special values such as

     * {@link #DEFAULT_SUBSCRIPTION_ID}. It can be used for subscription functions.

     * <p>A usable subscription ID is a valid subscription ID, but not necessarily an active

     * subscription ID (see {@link #isActiveSubscriptionId(int)}). Some subscription APIs

     * require a usable subscription ID, and this is noted in their documentation; otherwise, a

     * subscription ID does not need to be usable for subscription functions, only valid.

     *

     * @param subscriptionId the subscription ID

     * @return {@code true} if the subscription ID is usable; {@code false} otherwise.

    }

    /**

     * Checks if the supplied subscription ID corresponds to an active subscription.

     * Checks if the supplied subscription ID corresponds to a subscription which is actively in

     * use on the device. An active subscription ID is a valid and usable subscription ID.

     *

     * @param subscriptionId the subscription ID.

     * @return {@code true} if the supplied subscription ID corresponds to an active subscription;