java中的String和StringBuffered

public class String_Problem {
    public static void main(String[] args) {
        String s = null;
        s = s.toString() + 1;

//s = s+1;
此语句可以解释为
        //StringBuilder sb = new StringBuilder();
        //sb.append(s);
        //sb.append(1);
        //s = sb.toString();

        System.out.println(s);
    }
}