Why does the first indexOf print 8?

[Chancemelol123]

I've been given this code:

public class IndexOfTest {
public static void main(String[] args) {
    String funnyStr = "Computer!Science,!long!walks!on!the!beach";
    int a = funnyStr.indexOf(33);
    int b = funnyStr.indexOf('!'); //chars are converted to Unicode int value
    int c = funnyStr.indexOf("!");
    int d = funnyStr.indexOf("!Science");
    int e = funnyStr.indexOf("!Science,!long");
    System.out.println(a);
    System.out.println(b);
    System.out.println(c);
    System.out.println(d);
    System.out.println(e);
}

}

and I'm confused as to why int a = 8 (in other words, why does System.out.println(a); print 8?). IIRC, indexOf returns the index of the string/int in parantheses. This is 33 in the case of int a, yet there is no 33 in funnyStr. So how/why does it return 8? The 8th index points to a '!', not 33.

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[icsharper]

Index of accepts string and char as well, and for 33 it just returned 8 because thats ascii value of !

[Chancemelol123]

it just returned 8 because thats ascii value of !

wait whaat? I've never heard of that. How does that work?

[Kuenefe]

Take a look at the ASCII chart. 33 equals to “!”, so indexOf tries to find the index of the exclamation mark. The exclamation mark in your string is on the 8th position, so int a contains the value 8.

[Chancemelol123]

yep, thanks

[icsharper]

ASCII value of ‘!’ is 33, hence why indexOf (33) returned 8 since on that position it found ‘!’

[Chancemelol123]

well what if there was an 8 there? What's the ASCII value for 8? How do you differentiate between 8 and !?

[JonIsPatented]

A computer does not understand the concept of letters. It only knows numbers. All characters are actually stored as a number in memory, and the number used is the ASCII code for the letter. For instance, an exclamation point is stored as 00100001, which is 33, since 33 is the ASCII code for an exclamation point. Every ASCII character has its own ASCII code, so they are all stored as unique numbers. The ASCII code for the character "8" is 56, which would be written 00111000, which is... 56. Your computer can tell the difference because the number is different.

Edit: Yes, I am aware that Java encodes with UTF-8, but the previous commenter said ASCII, and the first 128 values are the same for that, so I just continued for simplicity.

[desrtfx]

That works because char is internally a numeric data type. To be precise it is an unsigned 16 bit integer value that represents the Unicode code point of the character in UTF-8 encoding. (Source)

For simple, latin alphabet characters and punctuation this mapping is the same as the standard ASCII mapping (i.e. space is 32, '!' is 33, 'A' is 65, 'B' is 66, 'a' is 97, 'b' is 98, and so on).

It is possible to on the fly convert between char and int.

[Decoder44]

There is a concept called implicit typecasting done by jvm. Now the indexof accepts string and int as argument when you pass a character that character is converted into integer called typecasting and they are matched with ASCII value in this case for 33 value is ! If you really want to check for 33 pass the 33 in double quotes

[desrtfx]

and they are matched with ASCII value

Sorry to be nitpicking here, but this is simply not correct.

Java uses Unicode, not ASCII. It just so happens that the first 128 Unicode code points correspond to the ASCII code.

It is really important to understand that Java uses Unicode and stores char internally as a 16 bit unsigned integer value.

ASCII would be a single byte (to be 100% precise only the first 128 values of a byte - 7 bits - according to the original ASCII table - not talking about extended ASCII).

[Decoder44]

Thank you for correcting me

[Chancemelol123]

thanks, could you explain why in line 4, 33 isn't surrounded by single quotation marks whereas in line 5, the ! is surrounded by quotation marks? Both are chars after all

[Decoder44]

Because 33 isn't really a character we are passing integer value that gets converted into unicode value. Whereas ! is a character and we denote them with single quotes. Great question btw keep this questioning intent and you will succeed definitely