Example of making TabAutoCompleat Commands bukkit&spigot

package org.golde.bukkit.tab; //name if your plugin (like a UUID but with words and dots)

import java.util.ArrayList;
import java.util.List;


import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;

import org.bukkit.plugin.java.JavaPlugin;

import org.bukkit.entity.*;

//Imports everything needed


public class MyPlugin extends JavaPlugin { //creates your plugin and tells the server to register your plugin as a bukkit plugin


	//when the server enables the plugin print a message in the console saying that it has been enabled

	public void onEnable() {
		getCommand("tab").setExecutor(this);   //tells bukkit to register a command
		getLogger().info("TAB plugin is starting."); //prints message
	}


	//when the server disables the plugin print a message in the console saying that it has been disabled
	public void onDisable() {
		getLogger().info("TAB plugin in stopping."); //prints message
	}


	//
	public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
		if(cmd.getName().equalsIgnoreCase("tab")){ // your command name
			if (! (sender instanceof Player)) //this makes sure its a player executing the command
				return true;

			//argument checker and definer
			//also prints the correct syntax if the user gets it wrong
			if(args.length < 2 ){
				sender.sendMessage("Incorrect Syntax!!"); //prints "incorrect syntax"
				sender.sendMessage("/tab <1-2> <a-b>"); // prints the correct syntax
				return true;
			}




			//Store which argument goes with which possibility
			String S12 = args[0]; //first argument
			String Sab = args[1]; //second argument





			if(S12.equalsIgnoreCase("1")){ //Retrieving and plugging in the arguments that are stored and running different commands depending on which arguments are were
				if(Sab.equalsIgnoreCase("A")) //Retrieving and plugging in the arguments that are stored and running different commands depending on which arguments are were
					sender.sendMessage("1 a"); //sends a message to the player who send the command depending what the arguments are
				else
					sender.sendMessage("1 b"); //sends a message to the player who send the command depending what the arguments are
			}
			else
			{
				if(Sab.equalsIgnoreCase("a")) //Retrieving and plugging in the arguments that are stored and running different commands depending on which arguments are were
					sender.sendMessage("2 a"); //sends a message to the player who send the command depending what the arguments are
				else
					sender.sendMessage("2 b"); //sends a message to the player who send the command depending what the arguments are
			}
		}
		return false; //this is a little confusing but just put it there
                     //it just returns false if nothing matches the arguments needed
	}





	//list all possible tab arguments

	public List<String> onTabComplete(CommandSender sender, //registers the auto tab completer
            Command command,
            String alias,
            String[] args){
		if(command.getName().equalsIgnoreCase("tab")){  //your command name
				List<String> l = new ArrayList<String>(); //makes a ArrayList


				//define the possible possibility's for argument 1
				if (args.length==1){
					l.add("1"); //Possibility #1
					l.add("2"); //Possibility #2


				}

				//define the possible possibility's for argument 2
				else if (args.length==2){
					l.add("a"); //Possibility #1
					l.add("b"); //Possibility #2


				}





				return l; //returns the possibility's to the client


            }
		return null; //this is a little confusing but just put it there
		             //it just returns NULL if absolutely nothing has happened
}}