Error in conversion of upper and lower cases

Below code is to convert upper case to lower case and vice vers?

if(s1.charAt(i)>=97 && s1.charAt(i)<=122){
s1.charAt(i)=s1.charAt(i)-32;
}
else if(s1.charAt(i)>=65 && s1.charAt(i)<=90){
s1.charAt(i)=s1.charAt(i)+32;
}


Please refer above and help what is the issue with this program?

Possible duplicate of Replace character in StringBuilder
– Shubhendu Pramanik
Jun 29 at 10:08

what is s1? a String? String is immutable, cannot be changed; anyway charAt is a method that returns a char, you cannot assign a new value to that returned value.
– Carlos Heuberger
Jun 29 at 10:15

s1

String

charAt

2 Answers
2

You have a problem here :

s1.charAt(i) = s1.charAt(i) - 32;
------------ -----------------
1 2


Here there are two problems :

Instead I would use :

String s1 = "AbCd";
//create a char array
char array = s1.toCharArray();
//loop over this array, and work just with it
for (int i = 0; i < array.length; i++) {
if (array[i] >= 'a' && array[i] <= 'z') {
array[i] = (char) (s1.charAt(i) - 32);//<--------------------------note this
} else if (s1.charAt(i) >= 'A' && s1.charAt(i) <= 'Z') {
array[i] = (char) (s1.charAt(i) + 32);
}
}

//when you end, convert that array to the String
s1 = String.valueOf(array);//output of AbCd is aBcD


Beside I would like to use :

String result = "";
for (int i = 0; i < array.length; i++) {
if (Character.isLowerCase(array[i])) {
result += Character.toUpperCase(s1.charAt(i));
} else {
result += Character.toLowerCase(s1.charAt(i));
}
}


would it be more readable to use 'a', 'z', ... instead of the integer values?
– Carlos Heuberger
Jun 29 at 10:20

'a'

'z'

exactly @CarlosHeuberger edit it thank you
– YCF_L
Jun 29 at 10:23

eventually32 = 'A' - 'a' + 1 (no so sure if that improves that much... it also needs casting, and may be confusing)
– Carlos Heuberger
Jun 29 at 10:28

32 = 'A' - 'a' + 1

this is true @CarlosHeuberger but instead I would like to use my second solution
– YCF_L
Jun 29 at 10:33

agreed, the second solution is much easier to understand
– Carlos Heuberger
Jun 29 at 11:24

Your code doesn't even compile, you can't do s1.charAt(i) = 'x', because s1.charAt is not a variable, you can't just assign anything to it.

s1.charAt(i) = 'x'

s1.charAt

To replace a character by index in a String, do:

new StringBuilder(yourString).setCharAt(characterIndex, 'x')

new StringBuilder(yourString).setCharAt(characterIndex, 'x')

I suggest using some IDE like Intellij or Eclipse, it will tell you about compile errors like those.

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