In Java, you cannot directly write the executable statements in class. You need to move your code in a method. Only variables declaration is allowed outside the method/blocks. Just for the sake of testing, ,move everthing to main method. Try this:
public class Orders {
public static void main(String argsp[]) {
String alphabet = "abc";
ArrayList<String> list = new ArrayList<String>();
int n = alphabet.length();
Random rand = new Random();
for (int i = 0; i < 10000; i++){
char a = alphabet.charAt(rand.nextInt(n));
char b = alphabet.charAt(rand.nextInt(n));
char c = alphabet.charAt(rand.nextInt(n));
String s = Character.toString(a) + Character.toString(b) + Character.toString(c);
if(list.indexOf(s) == -1){
list.add(s);
}
}
System.out.println(list);
}
}
Note: system.out.println(arrayList); will throw an error because there is no varaible called arrayList, i think it should be replaced with variable list. Also system should be System.