You must use arrays for this task:

import java.util.Scanner;
 
public class GhettoNumeralSystem07 {
    public static void main(String[] args) {
        Scanner console = new Scanner(System.in);
 
        char[] input = console.nextLine().toCharArray();
 
        StringBuilder sb = new StringBuilder();
 
        for (int i = 0; i < input.length; i++) {
            if (input[i] == '0') {
                sb.append("Gee");
            }
            else if (input[i] == '1') {
                sb.append("Bro");
            }
            else if (input[i] == '2') {
                sb.append("Zuz");
            }
            else if (input[i] == '3') {
                sb.append("Ma");
            }
            else if (input[i] == '4') {
                sb.append("Duh");
            }
            else if (input[i] == '5') {
                sb.append("Yo");
            }
            else if (input[i] == '6') {
                sb.append("Dis");
            }
            else if (input[i] == '7') {
                sb.append("Hood");
            }
            else if (input[i] == '8') {
                sb.append("Jam");
            }
            else if (input[i] == '9') {
                sb.append("Mack");
            }
        }
        System.out.println(sb.toString());
    }
}