Security - My solution to the SoloLearn "Security" code coach, allows for more than one thief

Security.java

import java.util.Random;
import java.util.Scanner;

public class Security {
    public static void main(String[] args) {
        //runServerTests();
        randomFloor();
    }

    /**
     * In a casino, given one money location, any number of thieves, and any number of guards,
     * returns "ALARM" if there is no guard between a thief and the money.
     * @param floorLayout A string of characters that includes $ (money), T (thief), and G (guard),
     *     that represents the layout of the casino floor.
     *     Space on the casino floor that is not occupied by either money, the thief, or a guard
     *     is represented by the character x.<br>
     *     example: xxxxx$xxGxxxT
     * @return A string that says 'ALARM' if there is no guard between the money and a thief,
     *     or 'quiet' if the money is safe.
     * @throws IllegalArgumentException if the input string is invalid.
     */
    public static String security(String floorLayout) throws IllegalArgumentException {

        checkInput(floorLayout);
        int money = floorLayout.indexOf('$');
        int thief = floorLayout.indexOf('T');
        String[] denOfThieves = {"G","G"}; //initializes to "G"; If there is no thief method will return "quiet".

        if ((thief < money) && (thief != -1)) {
            thief = floorLayout.substring(0,money).lastIndexOf('T');
            denOfThieves[0] = floorLayout.substring(thief, money);
        }


        if(floorLayout.substring(money).contains("T")){
            thief = floorLayout.substring(money).indexOf('T');
            denOfThieves[1] = floorLayout.substring(money,money + thief);
        }

        for(String thieve : denOfThieves){
            if (!thieve.contains("G")) {
                return "ALARM";
            }
        }

        return "quiet";
    }

    /**
     * Checks if casino floor layout input is valid for this program
     * @param floorLayout A string of characters that includes $ (money), T (thief), and G (guard).
     */
    private static void checkInput(String floorLayout){
        if(!floorLayout.matches("^[xGT$]+$"))
            throw new IllegalArgumentException("Invalid casino floor layout");
        int money = floorLayout.indexOf('$');
        if ((money == -1) || (floorLayout.substring(money+1).contains("$")))
            throw new IllegalArgumentException("Too much or too little money to guard");
    }

    /**
     * Creates a random floor layout and uses security() to see if the money is in danger,
     * then outputs the layout and result to the console.
     */
    static void randomFloor(){
        Random random = new Random();
        StringBuilder floorLayout = new StringBuilder();
        int floorLayoutLength = random.nextInt(11) + 11;
        //System.out.println(floorLayoutLength);
        for(int i = 1; i <= floorLayoutLength; i++){
            int thiefOrGuard = random.nextInt(11) + 1;
            if(thiefOrGuard < 2) {
                floorLayout.append("G");
            } else if(thiefOrGuard == 11) {
                floorLayout.append("T");
            } else floorLayout.append("x");
        }
        int theMoney = random.nextInt(floorLayoutLength-1);
        floorLayout.replace(theMoney,theMoney,"$");
        System.out.println(floorLayout);
        System.out.println(security(String.valueOf(floorLayout)));
    }

    /**
     * Uses Scanner to accept input from test case servers and
     * uses System.out to output the result of security(input).
     */
    static void runServerTests(){
        Scanner scanner = new Scanner(System.in);
        String floorLayout = scanner.nextLine();
        System.out.println(security(floorLayout));
    }

    /**
     * Runs a series of String literal test cases on security().
     */
    static void testCases(){
        //TEST CASES
        System.out.print("\nTest Case: " + "xxTxx$xxGxx" + "\nExpect: " + "ALARM" + "\nActual: ");
        System.out.print(security("xxTxx$xxGxx")); //ALARM

        System.out.print("\n\nTest Case: " + "xxGxx$xxTxx" + "\nExpect: " + "ALARM" + "\nActual: ");
        System.out.print(security("xxGxx$xxTxx")); //ALARM

        System.out.print("\n\nTest Case: " + "xTxGx$xTxGx" + "\nExpect: " + "ALARM" + "\nActual: ");
        System.out.print(security("xTxGx$xTxGx")); //ALARM

        System.out.print("\n\nTest Case: " + "x$xTxxGxxTx" + "\nExpect: " + "ALARM" + "\nActual: ");
        System.out.print(security("x$xTxxGxxTx")); //ALARM

        System.out.print("\n\nTest Case: " + "xTxxGxxTx$x" + "\nExpect: " + "ALARM" + "\nActual: ");
        System.out.print(security("xTxxGxxTx$x")); //ALARM

        System.out.print("\n\nTest Case: " + "GTxxx$xxxGx" + "\nExpect: " + "ALARM" + "\nActual: ");
        System.out.print(security("GTxxx$xxxGx")); //ALARM

        System.out.print("\n\nTest Case: " + "xxxxxxxGTx$" + "\nExpect: " + "ALARM" + "\nActual: ");
        System.out.print(security("xxxxxxxGTx$")); //ALARM

        System.out.print("\n\nTest Case: " + "$xxxxxxTGxx" + "\nExpect: " + "ALARM" + "\nActual: ");
        System.out.print(security("$xxxxxxTGxx")); //ALARM

        System.out.print("\n\nTest Case: " + "Txxxxxxxxx$" + "\nExpect: " + "ALARM" + "\nActual: ");
        System.out.print(security("Txxxxxxxxx$")); //ALARM

        System.out.print("\n\nTest Case: " + "$xxxxxxxxxT" + "\nExpect: " + "ALARM" + "\nActual: ");
        System.out.print(security("$xxxxxxxxxT")); //ALARM

        System.out.print("\n\nTest Case: " + "xxTxxGxx$xx" + "\nExpect: " + "quiet" + "\nActual: ");
        System.out.print(security("xxTxxGxx$xx")); //quiet

        System.out.print("\n\nTest Case: " + "xx$xxGxxTxx" + "\nExpect: " + "quiet" + "\nActual: ");
        System.out.print(security("xx$xxGxxTxx")); //quiet

        System.out.print("\n\nTest Case: " + "xTxGx$xGxTx" + "\nExpect: " + "quiet" + "\nActual: ");
        System.out.print(security("xTxGx$xGxTx")); //quiet

        System.out.print("\n\nTest Case: " + "x$xGxxGxxTx" + "\nExpect: " + "quiet" + "\nActual: ");
        System.out.print(security("x$xGxxGxxTx")); //quiet

        System.out.print("\n\nTest Case: " + "xxGxx$xxGxx" + "\nExpect: " + "quiet" + "\nActual: ");
        System.out.print(security("xxGxx$xxGxx")); //quiet
    }
}