I accidently opened a java file with something else, How do I change it back?

A few months ago I recently got Minecraft for PC and I was doing al these things with forge and mods when I accidently opened the java file thing with something else. By java file thing its when you download a mod and it shows the java symbol. So if anyone knows how to turn it back please help me it didn't bother me at first, but now its important and I need to change it.

Minecraft randomly got laggy when using shaders?

Ok, so right off of the bat, I'm going to list my pc's specs: Dell Inspiron 560, Windows 10, Intel Core i3, 6GB of Ram. Two weeks ago I was using a GTX 460 for a GPU. With that setup, I would get about 30-40 fps while using a shaders mod, SEUS specifically. Yesterday, my oldest bro came over with his wife and two little kids and he sold me his old GPU, a GTX 660, which I installed on my pc immediately. My nephew, who I just mentioned came with him, always likes to play Minecraft while over at my house. So opened minecraft and saw it was running just as smooth as before, about 50 fps or so.

Now, the next day, or today to be more precise, I decide to get on minecraft myself. When I get on any world, whether it be local or online, I only get 10 to 15 fps with shaders on. With them off, I'm getting 80 fps. It's not the GPU as other games run great on it. What in the world would cause Minecraft to run great one day, but terribly the next? I've checked all of the settings and nothing has been changed at all from what I can see…

Will a dell optiplex 780 be good for?

Light gaming like left 4 dead 2. Minecraft. Roblox. Garrys mod? Please Help I been looking at cheap pc for gaming for over 8 hours my budget is 100$

Getting Forge 1.9 to work with Optifine HD 1.9?

For the love of everything that is good and holy… Here's the situation… So I'm trying to get Forge 1.9 (using the installer) to play nice with 1.9 Optifine… (and if I ever get those to work together, I also need to tack on Liteloader). So there are 7 billion versions of Optifine I see, but no real clarifications on what the dumb letters mean at the end of the name. So I downloaded Optifine 1.9 HD. I followed what every tutorial on the internet says of installing forge and then install Optifine, but it crashes every time.
So I'm really new to modding… But I've gotten other mods to work… Just not stupid Optifine. Please help? Am I missing something obvious?

If I ever get this working, I will also need to add liteloader onto it too… But the liteloader 1.9 beta installer works like a dream so I don't think there will be many problems? Maybe?

Minecraft forge 1.9 problem?

I'm updating my mod to 1.9 today, but i've soon noticed an issue with fluids. They are considered as solid blocks, therefore i can't "dive" in them, i can literaly walk on water.

Can't install optifine for Minecraft?

Whenever I download Optifine, it-and all my other mods- have the WinRAR symbol instead of java, I've renamed them but they stay the same and Optifine gives me an error. How can I fix this?

Added (1). I'm using Windows 10

How To Make A Beach In A Superflat World? (Minecraft)?

So superflat worlds in Minecraft have no scenery whatsoever.Is it possible to use any mods or anything to make a beach without spending ages digging out land and filling it with water from a bucket?

What programming language is best for me?

I want to be able to make mods for games, such as minecraft, or civilization 5 or skyrim, and to be able to make miniature anti virus programs and something that is modern and will not be obsolete for years to come. Something that will also be considered a real world skill. Would would the best choice be? It doesn't have to meet all of the goals, i want it to be modern for sure