I think I kind of fixed my problem. Here's my code:

Code:
public class Card {

    int suit, rank;
    int index = 0;
    Card[] deck = new Card [52];
        
    public Card () {
        this.suit = 0; this.rank = 0;
    }

    public Card (int suit, int rank) {
        this.suit = suit; this.rank = rank;
    }

    public void main(String[] args) {
        for (suit = 0; suit <= 3; suit++) {
            for (rank = 1; rank <= 13; rank++) {
                deck[index] = new Card (suit, rank);
                index++;
            }
        }
        isFlush(deck,6);
    }

    public boolean isFlush(Card[] x, int y) {
        int count = 0;
        for(index = 0; index < y; index++){
            boolean comp = compareCard(x[index], x[index + 1]);
            if (comp = true){
                count++;
            }
        }
        if (count >= 5){
            System.out.println("Congratulations! You have a flush!");
            return true;
        }
        else{
            System.out.println("Sorry, you do not have a flush.");
            return false;
        }
    }

    public boolean compareCard(Card c1, Card c2){
        if (c1.suit != c2.suit){
            return false;
        }
        return true;
    }

}
But now I'm getting this error:

java.lang.NoSuchMethodError: main
Exception in thread "main"
Exception in thread "main" Java Result: 1

I know I have to make my main method static but how can I reference my non static variables from main? Or what other workaround can I use to get this to work? Any help is appreciated.