返回hi出现的次数

Question

I'm doing some coding bat exercises and I don't quite understand what's going on inside the for-loop.

    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;
}

Why is it str.length()-1? If I changed that to just str.Length I get an error: Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 5

Answer 1

Think about this part:

str.substring(i, i+2)

When i is equal to the length of the string, i + 2 will overshoot the end of the string by 1, giving you an out of bounds error.

Answer 2

这是因为您在str.substring（i，i + 2）中使用了i + 2，这会导致超出范围的异常。

Answer 3

When you use str.length() it gives you the length of the string, while the max index of string that is accessible is given by str.length() - 1 . For example, "String" will have length of 6. So, when you try to do this str.substring(5 , (5+ 2)) it will try to access the index which is out of the bound and hence it throw the exception.