There are no compiler errors but it didn't change the string

Question

I'm trying to write a program that changes the case of two characters in a string (change uppercase to lowercase and vice versa).It compiled, but the string is the same.

String newChar1 = caseChanger("DcoderIsCool", 3); 
String newChar2 = caseChanger("DcoderIsCool", 8);

I think the problem is with the method i used:

public static String caseChanger (String s, int ind) {
    if(!(Character.isUpperCase(s.charAt(ind)))) { 
        //checking if the character is uppercase or lowercase
        return s.substring(ind, ind + 1).toLowerCase();
    } else {
        return s.substring(ind, ind + 1).toUpperCase();        
    }
}

The output should have been "DcoDerIscool", but it's "DcoderIsCool" (the original string).

https://stackoverflow.com/questions/1552301/immutability-of-strings-in-java — Murat Karagöz, Jul 15 '19 at 10:42
Also, assuming that by "errors" you mean "compiler errors", "There are no errors" is a rather low bar to clear. You also need to check for logical error, which the compiler can't know about. — Federico klez Culloca, Jul 15 '19 at 10:45
Check your condition: if character is *not* uppercase, you convert it to lower case. That doesn't seem right... — Federico klez Culloca, Jul 15 '19 at 10:47
it works now. thank you to all of you! i wasn't sure what the ! meant, i copied that from an answered question — BumbleBee, Jul 15 '19 at 10:50
As a general rule, don't use code you don't understand. This is just one way it could go wrong. But it could go much worse. Also, read some basic java tutorial. And good luck with your learning :) — Federico klez Culloca, Jul 15 '19 at 10:52
yeah, you're right. thank you! i'm still learning the basics :) — BumbleBee, Jul 15 '19 at 10:55

score 1 · Accepted Answer · answered Jul 15 '19 at 11:08

Hope I understood your question right.

below code will give you output DcoDerIsCool and DcoderIscool.

public static String caseChanger(String s, int ind) {

    char[] charArr = s.toCharArray();

    if (!(Character.isUpperCase(s.charAt(ind)))) {
        charArr[ind] = Character.toUpperCase(s.charAt(ind));
    } else {
        charArr[ind] = Character.toLowerCase(s.charAt(ind));
    }
    return String.valueOf(charArr);
}

jstuartmilne · Answer 2 · 2019-07-15T18:05:12.607

0

I Think this is what you are looking for

public static String caseChanger (String s, int ind) {
    if((Character.isUpperCase(s.charAt(ind)))) { //checking if the character is uppercase or lowercase

        return new StringBuilder(s).replace(ind,ind+1,s.substring(ind, ind + 1).toLowerCase()).toString();
    }
    else {
        return new StringBuilder(s).replace(ind,ind+1,s.substring(ind, ind + 1).toUpperCase()).toString();        }
}

So you are changing only n charecter and returning those changed charecteres beside the extra not ! you are adding meaning your if condition is the other way arround. But what you are looking for is to replace the chars at the position you want in the original String. if im not mistaken. Hope it helps

edited Jul 15 '19 at 18:05

answered Jul 15 '19 at 10:55

jstuartmilne

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thank you! as suggested, i removed the "!" and it works now, but your code is more straight-forward, so i will also change the return statements :) – BumbleBee Jul 15 '19 at 11:05
1

Use StringBuilder, not StringBuffer. StringBuffer forces synchronization overhead on every method, which has no benefit in single-threaded logic, and rarely has any benefit even in multi-threaded logic. – VGR Jul 15 '19 at 15:59

score 0 · Answer 3 · answered Jul 15 '19 at 11:42

You fetched the character from string but didn't placed back into string s.substring(ind, ind + 1).toLowerCase() is applied to single character

Instead doing return s.substring(ind, ind + 1).toLowerCase();

Replace the CaseChanged character back into the original string.

There are no compiler errors but it didn't change the string

3 Answers3