Java String ReplaceFirst

Question

I am reading in a string

Is Mississippi a State where there are many systems.

I would like to replace the 1st "s" or "S" in each word with "t" or "T" (i.e keeping the same case)...so that the output is:

It Mitsissippi a Ttate where there are many tystems.

I have tried

s= s.replaceFirst("(?i)S", "t"); [which of course didn't work]

and have experimented trying to split the string using a string [] .split(Pattern.quote("\\s")) then trying to figure out how to replaceFirst() each element of the array and then return the values back to a string [but couldn't figure out the right way of doing it].

I thought \\G might help to restart at the next word but have gotten no where. Any help using these 3 methods is appreciated.

Why do you replace 'Is' to 'It' if you only need to replace the 1st 's' or 'S' in each work ? Can you correct the layout and give one or more clear example ? — Benoit Vanalderweireldt
– Benoit Vanalderweireldt, Commented Mar 31, 2016 at 4:42
@Hedgebox I hope you have got your answer. But have provided a different approach to solve your problem. See my answer. — mmuzahid
– mmuzahid, Commented Mar 31, 2016 at 5:36
One liner in JavaScript: .replace(/(\S*?)([sS])(\S*)/g, (_, $1, $2, $3) => $1 + ($2 == 's' ? 't' : 'T') + $3) — nhahtdh
– nhahtdh, Commented Mar 31, 2016 at 11:00

Tim Biegeleisen · Accepted Answer · 2016-03-31 08:20:06Z

10

One option would be to split the string into words, and then use String.replaceFirst() on each word to replace the first occurrence of s with t (or any other letter you want):

Update:

I refactored my solution to find the first occurrence of any s (upper or lower case), and to apply the appropriate conversion on it.

String input = "Is Mississippi a State where there are many systems.";
String[] parts = input.split(" ");
StringBuilder sb = new StringBuilder("");

for (int i=0; i < parts.length; ++i) {
    if (i > 0) {
        sb.append(" ");
    }
    int index = parts[i].toLowerCase().indexOf('s');
    if (index >= 0 && parts[i].charAt(index) == 's') {
        sb.append(parts[i].replaceFirst("s", "t"));
    }
    else {
        sb.append(parts[i].replaceFirst("S", "T"));
    }
}

System.out.println(sb.toString());

Output:

It Mitsissippi a Ttate where there are many tystems.

edited Mar 31, 2016 at 8:20

answered Mar 31, 2016 at 4:50

Tim Biegeleisen

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8 Comments

Thush-Fdo Over a year ago

@im-biegeleisen your solution is perfect with some adjustments. Check my post

clstrfsck Over a year ago

This gets the wrong result for a word like "Systems" with a capital "S" and lower case "s" (at least as I understood the question).

Tim Biegeleisen Over a year ago

Systems -> Tyttems ... what is the problem?

Hedgebox Over a year ago

@Tim Biegeleisen : msandiford seems to be correct... I just tried it...I would want "Systems" to become "Tystems"... only the 1st occurance of either "S" or "s" to "T" or "t"

Tim Biegeleisen Over a year ago

@BDCoder Sorry, I had a couple of typos in there. I have fixed them and I verified that the actual output matches what is expected.

|

mmuzahid · Accepted Answer · 2016-03-31 09:48:27Z

4

Approach-1: Without using replace and split method for better performance.

String str = "Is Mississippi a State where there are many systems.";
System.out.println(str);

char[] cArray = str.toCharArray();
boolean isFirstS = true;
for (int i = 0; i < cArray.length; i++) {
    if ((cArray[i] == 's' || cArray[i] == 'S') && isFirstS) {
        cArray[i] = (cArray[i] == 's' ? 't' : 'T');
        isFirstS = false;
    } else if (Character.isWhitespace(cArray[i])) {
        isFirstS = true;
    }
}
str = new String(cArray);

System.out.println(str);

EDIT: Approach2: As you need to use replaceFirst method and you dont want to use StringBuilder here is an option for you:

String input = "Is Mississippi a State where there are many Systems.";
String[] parts = input.split(" ");
String output = "";

 for (int i = 0; i < parts.length; ++i) {
     int smallSIndx = parts[i].indexOf("s");
     int capSIndx = parts[i].indexOf("S");

     if (smallSIndx != -1 && (capSIndx == -1 || smallSIndx < capSIndx))
         output += parts[i].replaceFirst("s", "t") + " ";
     else
         output += parts[i].replaceFirst("S", "T") + " ";
 }

System.out.println(output); //It Mitsissippi a Ttate where there are many Tystems.

Note: I prefer approach 1 because it has no overhead for the method replaceFisrt and split , String append or concat

edited Mar 31, 2016 at 9:48

answered Mar 31, 2016 at 4:47

mmuzahid

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8 Comments

mmuzahid Over a year ago

@cricket_007 edited by going to different approach :)

OneCricketeer Over a year ago

ASCII shifting... It'll work, but it is very specific to this one problem

mmuzahid Over a year ago

@cricket_007 yes.... but I hope this will provide a faster solution than other answer.

Hedgebox Over a year ago

@mmuzahid: tks for your solution but I am trying to get a better understanding of the uses of replaceFirst...without the use of StringBuilder at this point.

mmuzahid Over a year ago

@Hedgebox , Plz see EDIT part , May be it serve your purpose using replaceFirst

|

Thush-Fdo · Accepted Answer · 2016-04-01 07:19:07Z

3

Use below amendment to Tim Biegeleisen's answer (before editing his post)

String input = "Is Mississippi a State where there are many systems.";
String[] parts = input.split(" ");
StringBuilder sb = new StringBuilder("");

for (String part : parts) {
    sb.append(part.replaceFirst("s", "t").replaceFirst("S", "T"));
    sb.append(" ");
}

System.out.println(sb.toString());

Edit - You can use concat()

String input = "Is Mississippi a State where there are many systems.";
String[] parts = input.split(" ");

String output = "";

for (String part : parts) {
    output = output.concat(part.replaceFirst("s", "t").replaceFirst("S", "T") + " ");
}

    System.out.println(output);

Update

    String input = "Is Mississippi a State where there are many Systems.";
    String[] parts = input.split(" ");
    //StringBuilder sb = new StringBuilder("");

    String output = "";

    for (String part : parts) {
        output = output.concat(part.replaceFirst("s", "t") + " ");
    }

    String[] parts2 = output.split(" ");

    output = "";

    for (String part : parts2) {
        output = output.concat(part.replaceFirst("S", "T") + " ");
    }
    System.out.println(output);

edited Apr 1, 2016 at 7:19

answered Mar 31, 2016 at 4:56

Thush-Fdo

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8 Comments

Hedgebox Over a year ago

I do want to use String methods...is there a way to do it without using StringBuilder?

mmuzahid Over a year ago

@Hedgebox FYI StringBuilder provides better performance than +

Hedgebox Over a year ago

@Thush-Fdo: msandiford in his comment below...seems to be correct... I just tried it...I would want "Systems" to become "Tystems"... only the 1st occurance of either "S" or "s" to "T" or "t". When I changes "systems" to "Systems" the code produced "Tyttems" not "Tystems".

Thush-Fdo Over a year ago

@Hedgebox : Another solution to come up with this by using two loops as I've update my answer. But this cost your performance. Feel free to use any of the suggestions.

user5961012 Over a year ago

@Thush-Fdo dont take it other-wise, too many EDIT in your answer confused some people to understand.

|

Bilesh Ganguly · Accepted Answer · 2016-09-20 10:57:58Z

I've created a method that -

is general purpose,
doesn't use replace or split, and
only uses one loop.

The following is my code snippet:

public static String replaceFirstOccurance(String sentence, char toChange, char changeWith) {
    StringBuilder temp = new StringBuilder();

    boolean changed = false;
    for (int i = 0; i < sentence.length(); i++) {
        if (!changed) {
            if (sentence.charAt(i) == toChange) {
                temp.append(changeWith);
                changed = true;
            } else if (sentence.charAt(i) == Character.toUpperCase(toChange)) {
                temp.append(Character.toUpperCase(changeWith));
                changed = true;
            } else {
                temp.append(sentence.charAt(i));
            }
        } else {
            if (sentence.charAt(i) == ' ') {
                changed = false;
            }
            temp.append(sentence.charAt(i));
        }
    }

    return temp.toString();
}

Michael · Accepted Answer · 2016-03-31 04:48:11Z

1

My method would be less dependent on those string methods you've mentioned.

String phrase;
String [] parts = phrase.split(" ");

for (int i = 0; i < parts.length; i++ ) {
    for (int j = 0; j < parts[i].length(); j++) {
        if (parts[i].charAt(j) == 's') {
            parts[i] = "t" + parts[i].substring(1);
            break;
        } else if (parts[i].charAt(0) == 'S') {
            parts[i] = "T" + parts[i].substring(1);
            break;
        }
    }
}

String modifiedPhrase = "";

for (int i = 0; i < parts.length; i++ ) {
    modifiedPhrase += parts[i] + " ";
}

answered Mar 31, 2016 at 4:48

Michael

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Comments

Marco13 · Accepted Answer · 2016-03-31 13:03:46Z

1

There is also a nice, compact, stream-based solution for that:

String result = Stream.of(s.split(" "))
    .map(t -> t.replaceFirst("s", "t"))
    .map(t -> t.replaceFirst("S", "T"))
    .collect(Collectors.joining(" "));

answered Mar 31, 2016 at 13:03

Marco13

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Comments

score 0 · Accepted Answer · 2016-04-04 07:23:42Z

0

String ss = "Is Mississippi a State where there are many systems.";

String out = "";//replaced string
for (String s : ss.split(" ")) {
    int index = s.toUpperCase().indexOf('S');
    out += (s.replaceFirst("[s,S]", index!= -1 && s.charAt(index) == 'S' 
               ? "T" : "t")) + " ";
}

System.out.println(out);

edited Apr 4, 2016 at 7:23

answered Apr 3, 2016 at 7:00

user5896972

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