我不断收到此错误：线程“main”中的异常 java.lang.StringIndexOutOfBoundsException: String index out of range: 28

Question

This is my code :

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        String tweet = scan.nextLine();

        int link = 0;
        int tag = 0;
        int at = 0;
        int c = 0;
        int l = tweet.length();

        if (l <= 140) {
            while (c < tweet.length()) {
                char let = tweet.charAt(c);
                if (let == '#') {
                    tag++;
                    String hash = tweet.substring(c, c + 2);
                    if (hash.equals("# ")) {
                        tag--;
                    }

                } else if (let == '@') {
                    at++;
                    String to = tweet.substring(c, c + 2);
                    if (to.equals("@ ")) {
                        at--;
                    }
                } else if (let == 'h') {
                    String http = tweet.substring(c, c + 7);
                    if (http.equals("http://")) {
                        link++;
                    }
                }
                c++;
            }
            System.out.println("Number of Hashtags: " + tag);
            System.out.println("Number of Attributions: " + at);
            System.out.println("Number of Links: " + link);
        } else if (l > 140) {
            int difference = tweet.length() - 140;
            System.out.print("Excess Characters: " + difference);
        }

    }
}

Every time i run it I get the error:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 28
    at java.lang.String.substring(String.java:1951)
    at Main.main(Main.java:268)
    at Ideone.assertRegex(Main.java:110)

I was just wondering if there is a way to fix it?

Answer 1

Add a range check before your do subString because tweet.substring(c, c + 2); might cause index out of bound error when, for example, the tweet length is 7, c is currently 6, c+2 is 8, which exceeds the length.

if (let == '#') {
                tag++;
                if (c < tweet.length() - 2) { // make sure c+2 is in range for the substring function
                    String hash = tweet.substring(c, c + 2);
                    if (hash.equals("# ")) {
                        tag--;
                    }
                }

            } else if (let == '@') {
                at++;
                if (c < tweet.length() - 2) {// make sure c+2 is in range for the substring function
                    String to = tweet.substring(c, c + 2);
                    if (to.equals("@ ")) {
                        at--;
                    }
                }
            } else if (let == 'h') {
                if (c < tweet.length() - 7) {// make sure c+7 is in range for the substring function
                    String http = tweet.substring(c, c + 7);
                    if (http.equals("http://")) {
                        link++;
                    }
                }
            }