This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You can indeed do that using a decompiler, but don't expect that the output will be exactly the same as the original source code. Some information, like names of local variables, is lost in the compilation process, so it's impossible to get those names back by decompiling.