Adding some string before specific characters in Java

Question

I want to add "OB" before every vowel. Sample input: "THIS IS A TEST" Sample output: "THOBIS OBIS OBA TOBEST" I have no idea why my code doesn't work:

public static String obify(String test) {
    int x = 0;
    while (x != -1) {
        if (test.charAt(x) == 'A' || test.charAt(x) == 'E' || test.charAt(x) == 'I' || test.charAt(x) == 'O' || test.charAt(x) == 'U') {
            test = test.replace(test.substring(x, x+1), "ob" + test.substring(x, x+1));
            x += 3;
        } else {
            x++;
        }
        if (x >= test.length() - 1) {
            x = -1;
        }
    }
    return test;
}

[What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/q/25385173/5221149) — Andreas, Jul 26 '17 at 16:11
You could also just use `input.replaceAll("A", "OBA").replaceAll("E", "OBE")` and so on, or directly use regex `input.replaceAll("([AEIOU])", "OB$1")`. Also, what is the output of your current solution? — Zabuzard, Jul 26 '17 at 16:12
In what way is it not working? Does it fail with an error? If so, show us the stacktrace. Is the output incorrect? If so, show us what you get. — Andreas, Jul 26 '17 at 16:12
`replace` method replace all currencies of its first parameter. — talex, Jul 26 '17 at 16:23

score 4 · Answer 1 · answered Jul 26 '17 at 16:13

4

Perfect scenario for a simple regex

String foo = "hEllo what's up?";
String rep = foo.replaceAll("(?i)([aeiou])", "OB$1");
System.out.println(rep);

answered Jul 26 '17 at 16:13

baao

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2

While this solves the task OP tries to solve, it does not explain why his approach is not working as intended. – Zabuzard Jul 26 '17 at 16:15
also, wont this delete the vowel the OP intended on keeping? – Jason V Jul 26 '17 at 16:19
1

@Jason the $1 is the matched vowel – baao Jul 26 '17 at 16:21
Perfect, this was what I was going to answer as well. – Michael Hibay Jul 26 '17 at 16:53
thanks man. although i don't understand about it since i'm still new to this. but i'll get back to it later – Blah Blah Jul 29 '17 at 20:34
You’ll get additional information from reading the comments @BlahBlah also read about regex, it’s pretty helpful. Please mark the answer as accepted. – baao Jul 29 '17 at 20:40

score 0 · Answer 2 · answered Jul 26 '17 at 16:28

You should replace

test = test.replace(test.substring(x, x+1), "ob" + test.substring(x, x+1));

with

test = test.substring(0, x) +
        "ob" +
        test.substring(x, x + 1) +
        test.substring(x + 1);

Your problem is that replace act on all occurrences of its first parameter.

When you have "THobIS IS A TEST" and try to replace marked letter you replace both "I" letter. After it you index points to completely wrong position before second "I". Sooner or later you get to it again and situation repeats.

score 0 · Answer 3 · answered Jul 26 '17 at 16:36

Your problem is in replace call. Documentaion tells that it replaces each substring with new one. So your string grows infinitely: after first replace it is: "THobIS obIS A TEST" after next one is: "THobobIS obobIS A TEST" then "THobobobIS obobobIS A TEST" and so on...

If you change your line

test = test.replace(test.substring(x, x+1), "ob" + test.substring(x, x+1));

to

test = test.substring(0, x) + "ob" + test.substring(x);

it will do the work.

Also you can change while condition to x < test.length() and get rid of second if.

score 0 · Answer 4 · edited Jul 05 '18 at 13:35

I think it is easier this way: For the word "GTREIS": I basically take what was before and after the vowel(including the vowel) and attaching "OB"to the first part, attaching the remaining and finally replacing the original string with the modified one.

public static String  obify(String s)
{ 
    String inloc ="OB",aux="";
    String start="";
    int n=s.length();
    int i=0;

    while (i<n)
    {
        if(s.charAt(i)=='A'|| s.charAt(i)=='E' || s.charAt(i)=='I' ||     s.charAt(i)=='O'||s.charAt(i)=='U' ){
            inloc ="OB";
            start="";
            aux=s.substring(i);//EIS
            System.out.println(aux);
            start=s.substring(0,i);//GTR
            System.out.println(start);
            start=start+inloc;//GTROB
            System.out.println(start);
            start=start+aux;
            s=start;
            i+=3;// here you have to jump over OBE for example and search the next vowel 
            n+=2;
        } else {
            i++;
        }
    }
    return s;
}

Welcome to SO and thanks for answering. Please properly format and indent your code — Neuron, Jul 05 '18 at 13:18

Adding some string before specific characters in Java

4 Answers4