When launching the Minecraft game(I am using 1.8.9), on my dock on a Mac, I'll see two apps running related to it:
The grass block is labeled Minecraft, and it is the Minecraft launcher. The crafting table is labeled java, and it is the game itself.
I can right-click on Minecraft and quit it, and the game appears to be unaffected. I have launcher visibility in the profile unchecked, and the default is Close launcher when game starts. When I close java, Minecraft immediately closes too.
What is the purpose of running Minecraft while running java and what will quitting Minecraft affect?
Best Answer
Launchers are programs with usually a short interface which only influences some settings that may be not acessible on some situations during the actual game (Chosing DLCs to launch like in Crusader Kings II, Versions with Minecraft, or even visual settings). They generally also have a button (although the launcher may be automatic) which launches the game.
That is why you have two applications running, the launcher, which can launch the game, and the game, which is launched. They are not dependant of eachother, and as such, closing either the launcher or the game won't have influence over the other.
Java is a whole other subject. Java is a programming language, which can have a visual interface. Minecraft runs on Java. Closing Java is not a good idea, as it results on Minecraft losing its platform and closing. This can be useful if you can't exit minecraft (or you've opened several minecraft windows by mistake) and you wish to force a close on Minecraft.