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up vote 30 down vote favorite
9

I'm new to Java and I'm trying to replace a character at a specific index in a string. What I'm doing is:

String myName = "domanokz";
myName.charAt(4) = 'x';

this gives me error. It seems like charAt is readOnly. Is there any method to do this?

Thanks in advance!

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1  
I realize this has been answered to death, but it's worth noting that it is never allowed to assign the result of a function call in java. There are no such things as the references of C(?) and C++. – ValekHalfHeart Apr 14 at 0:11

7 Answers

up vote 58 down vote accepted

String are immutable in Java. You can't change them.

You need to create a new string with the character replaced.

String myName = "domanokz";
String newName = myName.substring(0,4)+'x'+myName.substring(5);

Or you can use a StringBuilder:

StringBuilder myName = new StringBuilder("domanokz");
myName.setCharAt(4, 'x');

System.out.println(myName);
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Ah, you mean like the replace method which will not modify the string but will just return a new string? – dpp Aug 5 '11 at 6:39
That's kinda complicated Mr.Petar. Is that the best way you to do it? Ah, I heard of StringBuilder before, does that make any difference? Will it give me an easier method? – dpp Aug 5 '11 at 6:41
yes, StringBuilder is mutable – Petar Ivanov Aug 5 '11 at 6:43
I know this is out of my original question, but can you please give me the solution in StringBuilder? Please, please? :D – dpp Aug 5 '11 at 6:44
Great! Thank you Sir! :D – dpp Aug 5 '11 at 6:47
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up vote 5 down vote

String is an immutable class in java any methods which seem to modify it always return a new string object with modification. if you want to manipulate a string consider StringBuilder or StringBuffer in case you require thread safety

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up vote 2 down vote

Turn the String into a char[], replace the letter by index, then convert the array back into a String.

String myName = "domanokz";
char[] myNameChars = myName.toCharArray();
myNameChars[4] = 'x';
myName = String.valueOf(myNameChars);
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up vote 0 down vote

I agree with Petar Ivanov but it is best if we implement in following way:

public String replace(String str, int index, char replace){     
    if(str==null){
        return str;
    }else if(index<0 || index>=str.length()){
        return str;
    }
    char[] chars = str.toCharArray();
    chars[index] = replace;
    return String.valueOf(chars);       
}
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4  
and what makes your solution better? – dpp May 3 '12 at 1:43
up vote 0 down vote

First thing I should have noticed is that charAt is a method and assigning value to it using equal sign won't do anything. If a string is immutable, charAt method, to make change to the string object must receive an argument containing the new character. Unfortunately, string is immutable. To modify the string, I needed to use StringBuilder as suggested by Mr. Petar Ivanov.

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up vote 0 down vote

I know this is an old post, but I am replying for the people who come to this from the search engines.

You can over-write a string, as follows: 

String myName = "halftime";
myName = myName.substring(0,4)+'x'+myName.substring(5);

Note that the string myName occurs on both lines, and on both sides of the second line.

Therefore, even though strings may technically be immutable, in practice, you can treat them as editable by over-writing them.

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up vote -3 down vote

this will work

   String myName="domanokz";
   String p=myName.replace(myName.charAt(4),'x');
   System.out.println(p);

Output : domaxokz

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yeah.. thanks.. – Diabolus Infernalis Aug 23 '12 at 16:37
1  
although i strongly detest this method of being allowed "editability" of other's work on this StackOverFlow site. thoroughly unfair :/ – Diabolus Infernalis Aug 23 '12 at 16:39
Syntax error. And even if corrected, say I want to replace the first 'o' with 'x', the second 'o' will be replaced too. – dpp Sep 7 '12 at 4:46

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