how to fix: Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException" for boolean array of random numbers in java

I am making a program where I get how many random numbers they want and the highest number they want to go up to, but when I run the code it does not give me the amount of numbers they asked for. it either gives me 1 number or none. Then it says "Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 9 at practice4.practice4.main(practice4.java:38)" in red.

double randomNum;
        int highestNumber, numsInLottery, display;
        boolean[] numberUsed;

        System.out.println("Welcome to the Lottery Number Generator!");

        System.out.println("How many numbers are in your lottery?");
        numsInLottery = TextIO.getInt();

        System.out.println("What is the highest possible number?");
        highestNumber = TextIO.getInt();


        numberUsed= new boolean [numsInLottery];

        for (int index = 0; index < numsInLottery; index++)
        {
        numberUsed [index]= false;

        while(index < highestNumber)
        {
            do
            {

                randomNum = Math.random() * highestNumber + 1;
                display = (int) randomNum ;

            } while (numberUsed [display - 1 ] ); 

        System.out.print(display + " ");
        numberUsed [display + ] = true;

        }   
        }
        }   
        }

before I had numberUsed= new boolean [numsInLottery]; I accidentally put highestNumber where numsInLottery is. when I had that it would give me all the numbers. but now that I have changed it it does not work any more this is what I get now

Welcome to the Lottery Number Generator!
How many numbers are in your lottery?
6
What is the highest possible number?
? 30
1 Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 21
    at practice4.practice4.main(practice4.java:35)