CODEWITHSUNDEEP
java
car
car

Reputation: 3

How to return a value from a matrix in java

I was reading about matrx in java and I found this method in my course page :

public int getSeatStatus(int row, char ch) { // Returns the status of the seat (row, ch)
return seats[row][(ch - ’A’)].getStatus();
 }

I do not understand how the method works .. as you can see that ch is not an index so why do they use it as an index ?

Can we rewrite this code in another simple way ? for example I tried to rewrite it like this : 

public int getSeatStatus(int row, char ch){
    int col = 0;
    if (ch == 'A') {
        col=0;
    } else if (ch == 'B') {
        col=1;
    }
    return s[row][col].getStatus();

}

Am I doing right ? Thanks

Upvotes: 0

Views: 353

Answers (4)

Abylay Sabirgaliyev
Abylay Sabirgaliyev

Reputation: 726

In Java, char is a numeric type. When you do char - ’A’, you operate with unicode code point. In case of 'A' - 'A', result is 0, when 'B' - 'A' result is 1, etc. It gives array indexes.

Upvotes: 1

tobi6
tobi6

Reputation: 8239

According to the ASCII standard the letter A has an integer value of 65 and Z of 90.

So, if you subtract A from the value of the given parameter, you get a value:

('B' - 'A') = (66 - 65) = 1
('F' - 'A') = (70 - 65) = 5

If you wanted to rewrite the rule for the whole alphabet, you would have to write 26 cases of recurring code.

Upvotes: 1

CloudPotato
CloudPotato

Reputation: 1275

You can convert a Character into an Integer. So you can also use it as an index. For example the output for System.out.println(0 + 'A') is 65.

Upvotes: 1

JohannisK
JohannisK

Reputation: 537

I wouldn't do it like that... If you have two 'ch' objects it's managable with if statements, but what if you have a 100? It would mean a unmaintable amount of if statements.

If you cast char 'A' to an int, the value is 65. By doing ch - 'A' you get 65 - 65 corresponding with index 0. If you cast char 'B' to an int, the value is 66. By doing ch - 'A' you get 66 - 65 corresponding with 1.

Your first example is in fact a better way to do this, and will work, even if the seats are "numbered" A till Z.

Upvotes: 2

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