先不管用不用String.split()

    public void evaluateCourse() {
//        Res res = new Res();
//        Connection con = null;
        String total = "1,2,33,53";
        String temp = "";
        for(int i = 0;i < total.length() ; i ++){
            temp += total.charAt(i);
            if(total.charAt(i) == ','){
                System.out.println(temp);
                temp = "";
            }
        }
    }

再看看用split的

public void evaluateCourse() {
//        Res res = new Res();
//        Connection con = null;
        String total = "1,2,33,53";
        String[] temp = aa.split(",");
        for(String s : temp) {
            System.out.println(s);
        }
    }

为什么不用String.split()？

Stream.of(total.split(",")).forEach(System.out::println);