My neighbour's dogs are always on a leash, but I understand how you feel about having a dog that jumps out at other dogs.
My dog likes to bark a lot. He barks at people, dogs, cars, loud noises etc. He really likes barking at people from the window too. When he's outside on a walk (on a leash) and he sees a car coming, or another dog or human, he'll jump at them and bark too. It is very difficult to correct.
From what I heard from a friend, pups at 4~7 months are supposed to be exposed to other dogs to get them used to them, but mine was not. My dog as a puppy, for about the first two years of his life, barely ever went outside and wasn't given proper training so I think he thinks he's the leader of the pack and doesn't behave properly, but I've been trying to correct his behaviour.
Anyway, this is getting long winded. What I've been doing with him is have him on his leash and whenever we go outside and see a person, car, or dog etc, I tell him "don't you dare" and hold onto his leash tightly, and if he barks or starts to jump, I tug his leash and make him sit or try to hold him down.
I've also tried getting him to play with other dogs, but he's very bad at socializing with them. My dog is also very very protective so I think that's why he barks at things near the house, or near his owners.
It is very very difficult to correct, but I've seen an improvement in him. He still lashes out at dogs, but is better with humans and barks a bit less. It takes a lot of persistence and dedication. It is more difficult to correct older dogs because it becomes a habit, but try to be more patient with them.
(My dog is almost 4 years old and is a maltese. My brother and his gf at the time were taking care of him for about the first 1 and a half years of his life and didn't train him properly. Due to circumstances, I took care of him for a year, and now my mother and I take care of him, but she undoes everything I do -.-)
Though, other people SHOULD have their dogs on leashes despite how well behaved the owners think their own dogs are.
"Even a broken clock is right twice a day."