This is a simple easy to do fix that allows you to add ls as a command simply open up your windows system32 folder.
This is normally C:\Windows\system32

Create a new file in this directory and name it “ls.bat” then right click and edit the file and add one single line.
dir

That simply calls the windows native dir command to list the contents of the current directory.

• Invoker
• Command

So what do they do and why are they usefull?

First there is a Command a command is any object that implements and interface.  That interface could be thought of as something as simple as follows:

// Command Interface
public interface Command {
     public void execute();
}

Now to explain the Invoker. The invoker looks for commands and then starts them that is all imagine a simple invoker as follows.

public void invoke(Command cmd){
     cmd.execute();
}

The function is simply passed a Command object and then executes it.

All that the invoker knows is that the object it receives is a command and that to “run” the command then it must call execute.

Think of a command line first, when you call a function say “ls” it looks for a “command” object named “ls” and then calls that objects “execute” function. This makes adding in new commands incredibly easy.

Command line example to hard? Think of it this way, A person(invoker) is executing a command. The command is “start car” the person calls “execute” on the “start car” command (like turning the key) and the car starts. What the car just physically accomplished to turn over and start is irrelevant to the person that turned the key all they knew is that they asked the command to run and it did.