look

public class Task04_1 {

    public static void main(String ... args){
        int r = 10;
        char[] line = new char[r*2+1];
        for(int i = 0; i< r;i++){
            int a = (int) Math.sqrt(r*r-(r-i)*(r-i));
            for(int j=0;j<r-a;j++){
                line[j]=line[r*2-j]='*';
            }
            for(int n=r-a;n<r+a+1;n++){
                line[n]='0';
            }
            System.out.println(line);
        }

        System.out.println(fillArray(line,0, 2*r,'0'));

        for(int i = r; i>0;i--){
            int a = (int) Math.sqrt(r*r-(r-i)*(r-i));
            for(int j=0;j<r-a;j++){
                line[j]=line[r*2-j]='*';
            }
            for(int n=r-a;n<r+a+1;n++){
                line[n]='0';
            }
            System.out.println(line);
        }

    }

    static char[] fillArray(char[] array, int startIndex, int endIndex, char simbol){
        for(int i=startIndex; i<=endIndex;i++) array[i] = simbol;
        return array;
    }
}