Sometimes it's necessary to see the Java source code corresponding to a .jar file. Here's how:

In a command shell:

java -cp "C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.2.3\plugins\java-decompiler\lib\java-decompiler.jar" org.jetbrains.java.decompiler.main.decompiler.ConsoleDecompiler -hdc=0 -dgs=1 -rsy=1 -rbr=1 -lit=1 -nls=1 -mpm=60 {.class or .jar file to decompile} {folder into which to write results}

For example:

java -cp "C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.2.3\plugins\java-decompiler\lib\java-decompiler.jar" org.jetbrains.java.decompiler.main.decompiler.ConsoleDecompiler -hdc=0 -dgs=1 -rsy=1 -rbr=1 -lit=1 -nls=1 -mpm=60 "C:\Program Files\Vault 3\vault_win.jar" c:\temp\decomp

The above command will write a .java source file if the input is a .class file. If the input is a .jar file, it will write a .jar file containing sources. You can easily navigate through the .jar file by adding ".zip" to its file name, and then navigating it with the Windows File Explorer.