If statement seems to skip though requirements are met

Question

I have a very simple question that I really can't understand.

I have a method that takes a string and determines what the first character of the string is, and then returns it.

public String deterFirstChar(String value){
    String keyValue;
    char res; 
    res = value.charAt(0);
    keyValue = Character.toString(res);
    if (keyValue == "C"){
        return keyValue;
    } else if (keyValue == "G") {
        return keyValue;
    }
    System.out.println("Error: Wrong keyParam");
    return "F";
}

However, intstead of returning, for an example keyValue = C, it skipps the if statement and returns "F" when I know for sure that keyValue is "C".

Why is this occurring?

Requirements are not met at all. See http://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java — Bart, Aug 06 '13 at 09:42
To compare two strings, you should use the equals method: if (keyValue.equals("C")) { — alfredaday, Aug 06 '13 at 09:43

score 7 · Accepted Answer · edited May 23 '17 at 12:20

7

First, check How do i compare string?

Secondly, you don't have to convert the char to String to check its value, you can do it like below

res = value.charAt(0);
//keyValue = Character.toString(res); NOT REQUIRED
if (res == 'C'){
    return Character.toString(res);
} else if (res == 'G') {

edited May 23 '17 at 12:20

Community

1
1

answered Aug 06 '13 at 09:42

sanbhat

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The method returns a String, so you'd either need to convert the char to string before returning or change the return type, too. – Rik Aug 06 '13 at 09:44
1

@sanbhat, upvote for the idea of converting character to String – Prasad Kharkar Aug 06 '13 at 09:55
Thanks for the answers, this works very well! I tried this at first, but I used "C" instead of 'C'. Is "" exclusive for strings? – Erik Soderstrom Aug 06 '13 at 10:04
Yes, `""` represents String and `''` represents character – sanbhat Aug 06 '13 at 10:10

Prasad Kharkar · Answer 2 · 2013-08-06T09:51:19.810

4

You should not compare strings using ==, use equals() method

 if (someString.equals("C")){
        return someString;
    } else if (someString.equals("G")) {
        return someString;
    }

== checks whether two variables refer to the same object.
equals() method checks whether the contents of the object are same or not.
so If == returns true, then equals() method also returns true because they are referring to the same object hence they are equal

You can find a great explanation for string comparison with equals and assignment If you want to use characters,

res = value.charAt(0);
if (res == 'C'){
    return Character.toString(res);
} else if (res == 'G') {
    return Character.toString(res);
 }

edited Aug 06 '13 at 09:51

answered Aug 06 '13 at 09:43

Prasad Kharkar

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May I please know the reason for downvote? so that I can correct myself? – Prasad Kharkar Aug 06 '13 at 09:47
Thanks, I didn't know this, now it works like a charm! However, it would work when comparing a, for example int like: if(int i = 1) {do stuff}? – Erik Soderstrom Aug 06 '13 at 09:53
This is because int is a primitive and comparison is different for object types and primitive types. – Prasad Kharkar Aug 06 '13 at 09:54

score 0 · Answer 3 · answered Aug 06 '13 at 10:16

0

Try this

public static char findFirstChar(String string){
    return string.charAt(0);
}
    char out = findFirstChar("Rakesh");
    System.out.println("First Character:"+out);

answered Aug 06 '13 at 10:16

Rakesh KR

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If statement seems to skip though requirements are met

3 Answers3