我面临java.lang.StringIndexOutOfBoundsException：

Question

我在运行此代码时收到java.lang.StringIndexOutOfBoundsException。我该如何解决这个问题？

import java.util.Scanner;

class C {
    static int Occurence = 0;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        StringBuilder sb = new StringBuilder();
        System.out.println(sb.deleteCharAt(3));
        for (int i = str.length() - 1; i > 0; i--) {
            Occurence = 1;
            for (int j = i - 1; j > 0; j--) {
                if (str.charAt(i) == str.charAt(j)) {
                    Occurence++;
                    sb.deleteCharAt(j);
                }
            }
            System.out.println(str.charAt(i) + " repeated " + Occurence);
        }
    }
}

Answer 1

// empty, current size 0    
StringBuilder sb = new StringBuilder();

// StringIndexOutOfBoundException bcoz current size is 0, and you are accessing index 3.
System.out.println(sb.deleteCharAt(3));