how to map char to int in java

Question

I'm very new to programming and can't resolve the following problem.

I have a list of coordinates in type char that I need to transfer to numbers (type int). So for example char a should be int 0, char b - int 1 etc. So I build the following code using a switch statement. I want to call it as a method but I keep getting the following error: this method must return a result of type int. Could somebody please explain what I'm doing wrong? I've also tried using return instead of int .. = 0; but that didn't help either.

    int x () {
        char ch = 'c';
        switch (ch)
        { 
        case 'a': 
            int a = 0;
            break; 
        case 'b': 
            int b = 1;
            break; 
        case 'c': 
            int c = 2;
            System.out.println(c); 
            break; 
        case 'd': 
            int d = 3;
            break; 
        case 'e': 
            int e = 4;
            break; 
        case 'f': 
            int f = 5;
            break; 
        case 'g': 
            int g = 6;
            break; 
        case 'h': 
            int h = 7;
            break; 
        }   
}

Instead of writing int a = 0, int b = 1 etc. You should just write return 0;, return 1; etc. And you don't need the breaks. — Sweeper
– Sweeper, Commented Oct 13, 2019 at 9:51
Then you don't need the breaks, as he/she/whatever does it, it's necessary. — Curiosa Globunznik
– Curiosa Globunznik, Commented Oct 13, 2019 at 10:45

Curiosa Globunznik · Accepted Answer · 2019-10-13 10:34:55Z

2

If your chars are just the same you mentioned you can use something like this.

static int toNumber(char chr) {
        return (chr - 97);
    }

The concept is this: a char is encoded as a byte, which is a number. Check out a related ASCII table where you can see that 'a' has the value 97 (decimal), 'b' has 98... So if we subtract 97 from all our chars we can reach the desired values.

    char   byte(decimal)   char value -97
    a        97                  0
    b        98                  1
    ...      ...                ...
    z        122                 24

But the problem with your function is the fact that the return statement was missing. You can make it work by changing it to this

int x() {
    char ch = 'c';
    int value = 0;
    switch (ch) {
        case 'a':
            value = 0;
            break;
        case 'b':
            value = 1;
            break;
        case 'c':
            value = 2;
            System.out.println(c);
            break;
        case 'd':
            value = 3;
            break;
        case 'e':
            value = 4;
            break;
        case 'f':
            value = 5;
            break;
        case 'g':
            value = 6;
            break;
        case 'h':
            value = 7;
            break;
    }
    return value;
}

edited Oct 13, 2019 at 10:34

Curiosa Globunznik

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answered Oct 13, 2019 at 9:58

Hadi Moloodi

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2 Comments

Curiosa Globunznik Over a year ago

A somehow related assignemt one can frequently see is is this one, also deals with char/byte tricks, which I tried to make as transparent as possible in the very looong answer at the end.

Curiosa Globunznik Over a year ago

Under the hood a number of implicit type conversions take place, from char 'a' to byte 97 to byte (97-97=0) to int for the return value 0(byte) -> 0(int) if I'm not mistaken. You can find more info and examples here and the complete oracle documentation here.

Sanower Tamjit · Accepted Answer · 2019-10-13 09:57:28Z

0

You can get it different ways.

int x = Character.getNumericValue('a');

or,

char a = 'a';
int x = a;

or,

int x = Integer.parseInt(String.valueOf('a'));

answered Oct 13, 2019 at 9:57

Sanower Tamjit

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