Java: getting the subscript of an array item

Question

In Java, I need to be able to get the subscript value of an array item. Say in a sting array, letters[25] stores the letter Z. If my user inputs a Z, I need to get that subscript value 25 as an integer (so I can plug it in later in another array that contains other correlated data).

My array letters[] has 26 elements, basically A through Z such that letters[0] = A and so on. I have another array containing integer values (also 26 total elements). Trying to convert letters to number values.

Possible duplicate of Java - how to convert letters in a string to a number? — OneCricketeer
– OneCricketeer, Commented Jun 18, 2017 at 13:32
Class java.util.Arrays has a lot of binarySearch methods. — Thomas Fritsch
– Thomas Fritsch, Commented Jun 18, 2017 at 13:33
Yeah... I was thinking the binarySearch methods might hold the key. Still working on it. As to why I am using basically a hash, well, I need to calculate based on the number value of letters that themselves can change depending on another part of the program. Thus making an array for just the letters and another for the variable integer values sort of made sense. I looked at hat other thread and the map option looks interesting but I am still thinking two arrays gives me the flexibility I need. — GDearth
– GDearth, Commented Jun 18, 2017 at 14:27

mrida · Accepted Answer · 2017-06-18 13:37:16Z

1

A character can be converted to a number by getting its ASCII code.

int ascii = (int) character;

Assume your characters are in lowercase, you need then to subtract 97 from the result integer which will give you the index of the character in your letters array.

answered Jun 18, 2017 at 13:37

mrida

1,1672 gold badges10 silver badges16 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

ernest_k · Accepted Answer · 2017-06-18 13:32:45Z

0

To find an index of an element in an array, you can use a binary search:

//First, sort the array:
java.util.Arrays.sort(letters);
int indexOfZ = java.util.Arrays.binarySearch(letters, "Z");

Please check the JavaDocs to see what to expect when the value is not found (it will be a negative int).

answered Jun 18, 2017 at 13:32

ernest_k

45.5k5 gold badges58 silver badges107 bronze badges

3 Comments

glglgl Over a year ago

But then you don't have the index in the original array unless the sort method would give you an index map array.

ernest_k Over a year ago

True. But sorting should not be necessary, as the array is already sorted as per the question. It's just a note that the array must be sorted to use binary search.

GDearth Over a year ago

Well... That was an abundance of options! Thanks I think I can figure it out from here. Basically taking a 'word' and then taking each letter thereof as a separate variable. Got most of the code done using an if loop and feeding an incrementing charAt into an array up to that 'word' length(). Sort of doing an analogy for genetics (hard to explain). Trying to work only off the standard libraries. Good point about converting to lowercase first too to avoid negative number errors from invalid references to my limited array. That would have otherwise lead to some bizarre calculation results.

fxrbfg · Accepted Answer · 2017-06-18 13:58:37Z

0

Simplest way (one of many) to do this is use String, it already have internal array. You need to have this code:

 public int indexOfLetter(String letter) {
    String alphabet = "abcdefghijklmnopqrstuvwxyz";
    int index = alphabet.indexOf(letter.toLowerCase());
    if (index == -1) {
        throw new RuntimeException("letter not found");
    }
    return index;
}

example:

System.out.println(indexOfLetter("z")); // 25
System.out.println(indexOfLetter("Z")); // 25

edited Jun 18, 2017 at 13:58

answered Jun 18, 2017 at 13:36

fxrbfg

1,7861 gold badge12 silver badges18 bronze badges

3 Comments

glglgl Over a year ago

What is the + 1 for?

fxrbfg Over a year ago

@glglgl array indexation from 0, and letter indexation in alphabet starts from 1, if we select "a" letter we get 0 index instead expected 1

glglgl Over a year ago

The OP states "If my user inputs a Z, I need to get that subscript value 25 as an integer". No word about that 1 is expected for A.

Collectives™ on Stack Overflow

Java: getting the subscript of an array item

3 Answers 3

Comments

3 Comments

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

3 Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related