java - 返回 hi 出现的次数

Question

我正在做一些编码 bat 练习，但我不太明白 for 循环内部发生了什么。

    public static int countHi(String str){
    int count = 0;

    // While i is less than the length of string increase the index by one
    // Checking the char at each index
    for(int i = 0; i < str.length()-1; i++){
        // Do i + 2 because hi has two letters
        // i = index 0 and add 2 so 0,1,2-- but 2 is exlcuded so check to see if index 0,1 equals "hi"
        if(str.substring(i, i+2).equals("hi")){
            count++;
        }
    }
    System.out.println("Hi appears: " + count + " times.");
    return count;
}

为什么是str.length()-1？如果我将其更改为 str.Length，则会出现错误: Exception in thread "main"java.lang.StringIndexOutOfBoundsException: String index out of range: 5

Answer 1

思考这一部分:

str.substring(i, i+2)

当i等于字符串长度时，i + 2将超出字符串末尾1，从而产生越界错误。