interface Upgrade {
    // common stuff for all upgrades
}

interface UniversalUpgrade {
    // marker interface, could also go with a boolean isUniversal() method in Upgrade
}

[abstract] class WeaponUpgrade implements Upgrade {
    // weapon specific stuff
}

[abstract] class ArmorUpgrade implements Upgrade {
    // armor specific stuff
}

class UpgradeManager {
    private Map<String, Upgrade> upgrades;

    public void registerUpgrade(String id, Upgrade upgrade) {
        upgrades.put(id, upgrade);
    }

    public Collection<UniversalUpgrade> universalUpgrades() {
        return upgrades.values().stream().filter(u -> u instanceof UniversalUpgrade).collect(Collectors.toList());
    }

    // or

    public Collection<Upgrade> universalUpgrades() {
        return upgrades.values().stream().filter(Upgrade::isUniversal).collect(Collectors.toList());
    }

    public Collection<WeaponUpgrade> weaponUpgrades() {
        return upgrades.values().stream().filter(u -> u instanceof WeaponUpgrade).collect(Collectors.toList());
    }

    public Collection<ArmorUpgrade > armorUpgrades() {
        return upgrades.values().stream().filter(u -> u instanceof ArmorUpgrade).collect(Collectors.toList());
    }

    public <U extends Upgrade> upgrades(Class<U> upgradeType) {
        return upgrades.values().stream().filter((u) -> upgradeType.isApplicableFrom(u.getClass())).collect(Collectors.toList());
    }
}