关于字符串数组中的String_Index_Out_Of_Bounds_Exception错误

Question

String array

I am new to Java and the issue here is not with the total code, it's with array size and out of boundaries issue. This code is supposed to simulate the hashing in Java but this is not the main issue though

Error : Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 2

//import org.w3c.dom.NameList;

public class hash {


  public static void main(String[] args) {

    int tablesize = 4;

    String[] Name = {
      "ALY",
      "om",
      "j",
      "l"
    };

    long Out = calc_hash(Name, tablesize);
    System.out.println(Out);
  }

  public static long calc_hash(String[] key, int table_size) {

    int i, l = key.length;
    long hash = 0;
    for (i = 0; i < l; i++) {

      hash += Character.getNumericValue(key[i].charAt(i));
      hash += (hash << 10);
      hash ^= (hash >> 6);
    }
    hash += (hash << 3);
    hash ^= (hash >> 11);
    hash += (hash << 15);
    if (hash > 0) return hash % table_size;
    else return -hash % table_size;
  }
}

Answer 1

I don't use Java, but looking at your code I notice this:

l = key.length

key is the string array, so its length is 4, therefore l = 4 . Then you use l as a limit for your loop, you increment i until l - 1 and you use i as an index for both elements in the array and char position in the string ( key[i].charAt(i) ). This means that if the second string doesn't have at least 2 chars, the 3rd doesn't have at least 3 and the 4th doesn't have at least 4, you will get the error you are getting.

Which value from each string do you want to use in each for cycle?

Answer 2

Problem seems to be in your logic. All the value in array Name are not of same length. Once value of i in for loop reach 2, key found is "j" which is of only length 1 and there will be no charAt(2). Not sure what you are trying to do here but if you have all the elements in array of lenght 4, problem will go away, try with.

        String[] Name = {
            "ABCD",
            "ABCD",
            "ABCD",
            "ABCD"
    };

Or maybe it's a typo, and should instead

hash += Character.getNumericValue(key[i].charAt(0));