Not able to access Minecraft.jar

There is a problem where when you try to open minecraft.jar in the bin folder, a message from Java Virtual Machine Launcher comes up and says "A Java Exception has occurred."

What I expected to happen was that when I pressed Minecraft.jar to open it to download mods it would open easily since I had 7-zip.
I though that I would be able to open it and delete the Meta-inf folder to download the mod optifine.

What actually happened was that a message from Java Virtual Machine Launcher came up and said "A Java Exception has occurred." This makes it impossible to download mods. I went to see If i had Java and I had. Now I had stuff like the magic launcher, but it did nothing to help.

Steps to see this happen
1. go to .minecraft
2. open bin folder
3. press the minecraft.jar