How to type unknown number of char element here(short program)

Question

public static GPA() {
int grades;
int numgrades=0;
char i;
ArrayList<Character> niz= new ArrayList<Character>();
Scanner s=new Scanner(System.in);
System.out.println("add char");

(HOW TO ADD CHAR ARRAY)
}

Answer 1

while((i=s.next().charAt(0))<0 ){
niz.add(i);
System.out.println(niz);

CAN I USE THIS?

Answer 2

there is problem how to stop input of chars

//this reads separate char<enter> and ends if user enters empty line
String str;
while( ! (str = s.nextLine()).isEmpty() )
niz.add(str.charAt(0));

// or you can get it as one String<enter>
for (char c: s.nextLine() .toCharArray() )
niz.add(c);