Judo, or any martial art, is a great self defense tool when you really know it. Most martial arts take at least four years to learn at a basic level. Before that, you may be able to use a trick or two and run away as fast as you can. I always tell my students that the best self defense is Run Quan Do. The moment you smell any possibility of danger, get away as fast as you can.
People often get a false sense of self confidence when they start training in a martial art. As long as you are aware of this, then learning a martial art can be so much more than learning to defend yourself.
Karate and Kung Fu also have many tripping and trapping techniques that, once dominated, can help you fight without hurting your opponent.