my german shepherd pup.. is nearly 4 months..
i dont know whether all this is my imagination or not but it makes me worry..

he's having real problems meeting with other dogs.. he never passes another dog without barking and growling at it. thats why i have real problems taking him out for a walk.. there'll be at least another 7 dogs on the road.. when he starts barking at them they pull their owners to come and give him a bite. he's already got attacked once and pounced on twice.even our neighbours dog which he sees everyday and barks at for hours continuosly... he doesnt drop it. i have no idea what to do. i'll be glad for some help.

he's 4 months old but he still eats rubbish like plastics , paper, mud, and not to forget his favorite- cement!!!!!

Firstly, stop worrying - your tension will be travelling down the lead and making your pup worse :(  It also sounds to me as if the other owners have a worse problem than you if they are being dragged by their own dog :(

I'd suggest taking your pup to a responsible trainer for puppy classes to start with, so he can learn appropriate behaviour with pups his own age, and then perhaps group pet obedience lessons so you can teach him not all dogs are like that, although you may have an uphil struggle if there are agressive dogs in the neighbourhood that he meets repeatedly.

Can you walk your pup at other times, so you don't meet the nasty dogs?

At 4 months he's teething AND exploring his world with the only thing he has - his teeth.  If you find him chewing something you think he shouldn't - distract him, call him to you and ask him to do something you've already trained him to do (like 'sit'), then give him a quick game, this way he will eventually forget those things were such fun....