How to replace two characters in a String with replace/regex?

Question

I want to modify two characters in the string, for example change each 'i' into 'e', and each 'e' into 'i' so text like "This is a test" will become "Thes es a tist".

I've made a solution that works, but it is boring and inelegant:

String input = "This is a test";
char a = 'i';
char b = 'e';

char[] chars = input.toCharArray();
for(int i = 0; i < chars.length; i++) {
    if(chars[i] == a) {
        chars[i] = b;
    }else if(chars[i] == b) {
        chars[i] = a;
    }
}

input = new String(chars);

How can this be accomplished with regex?

@feelingunwelcome that duplicate is about swapping two characters (changing their positions), while this is about changing characters with different ones while replacement characters doesn't even need to exist in original string at all. — Pshemo
– Pshemo, Commented Sep 22, 2018 at 11:50

Pshemo · Accepted Answer · 2018-09-21 14:51:51Z

5

Since Java 9 we can use Matcher#replaceAll(Function<MatchResult,String>). So you can create regex which will search for either i or e, and when it finds it let function pick replacement based on found value (like from map)

Demo

Map<String, String> replacements = Map.ofEntries(
        Map.entry("i", "e"), 
        Map.entry("e", "i")
);
String replaced = Pattern.compile("[ie]")
                         .matcher(yourString)
                         .replaceAll((match) -> replacements.get(match.group()));

But to be honest your solution doesn't look bad, especially if it is used for searching for single characters.

answered Sep 21, 2018 at 14:51

Pshemo

125k26 gold badges194 silver badges280 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Muhammad Yojer Over a year ago

That's a really cool solution, but I'm on Java 8, unfortunately.

Pshemo Over a year ago

I would like to remind that Java 11 will be released in this month. Anyway using map to pick replacement can be also applied in your own solution instead of ifs.

Mena · Accepted Answer · 2018-09-21 14:57:42Z

2

A less elegant solution than Pschemo's but usable since Java 8:

static String swap(String source, String a, String b) {
    // TODO null/empty checks and length checks on a/b
    return Arrays
        // streams single characters as strings
        .stream(source.split(""))
        // maps characters to their replacement if applicable
        .map(s -> {
            if (s.equals(a)) {
                return b;
            }
            else if (s.equals(b)) {
                return a;
            }
            else {
                return s;
            }
        })
        // rejoins as single string
        .collect(Collectors.joining());
}

Invoked on "This is a test", it returns:

Thes es a tist

Note

As mentioned by others, your solution is fine as is for single characters.

answered Sep 21, 2018 at 14:57

Mena

48.6k11 gold badges90 silver badges109 bronze badges

1 Comment

Pshemo Over a year ago

We can also use instead of ifs Map<String, String> replacements and map(s->replacements.getOrDefault(s,s)) to let s be returned in case when replacement doesn't have s key.

Collectives™ on Stack Overflow

How to replace two characters in a String with replace/regex?

2 Answers 2

2 Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related