substring - get a substring of a string

package homework;
//2、取出所有人的姓
public class practice_02 {
    public static void main(String[] args) {
        String str = "张飞,刘备,关羽,曹操,关平,貂蝉";
        //先将字符串分割然后存储进数组names
        String[] names = str.split(",");
        //循环遍历数组
        for (String name : names){
            //substring(起始下标,结束下标)取出字符串0-1（包含0不包含1）的子字符串
            String surname = name.substring(0,1);
            System.out.println(surname);
        }
    }
}