Swap two substring in a string in java

Question

I'm trying to analyze some text and I need to swap two substring in a string, for example in the following text I wanna swap "nice to see you" and "how are you"

Hi nice to see you? I'm fine Nice! how are you some other text

so the result should be :

Hi how are you? I'm fine Nice! nice to see you some other text

First I wrote this method and works fine for this simple example:

    public static String Swap(String source, String str1, String str2) {

    source=source.replace(str1, str2);
    source=source.replaceFirst(str2, str1);

    return source;
}

I need to use this method for more complex texts like the following one but as replaceFirst uses regex it cannot swap using my method.

        f(f(x))*g(g(x))

I wanna swap f(x) and g(x), but it won't word.

is there any other way to do this?

Answer 1

Try this:

source=source.replace(str1, str2);

// handle things like "f(f(x))*g(g(x))"
source=source.replaceFirst(Pattern.quote​(str2), Matcher.quoteReplacement(str1));

See the documentation for Pattern.quote here.

See the documentation for Matcher.quoteReplacement here.

Warning: This approach you have chosen has two big assumptions!

• Assumption #1: str2 must appear in the source before str1, and
• Assumption #2: str2 must only appear one time in the source string
• Furthermore: if one of the strings is a substring of the other, you will get unexpected results

A more general solution would be needed to eliminate those problems.

For example:

String longer = str1;
String shorter = str2;
if(str2.length() > str1.length()) {
    longer = str2;
    shorter = str1;
}
Pattern p = Pattern.compile(Pattern.quote(longer) + "|" + Pattern.quote(shorter));
Matcher m = p.matcher(source);
StringBuffer sb = new StringBuffer();
while (m.find()) {
    String replacement = str1;
    if(m.group(0).equals(str1)) {
        replacement = str2;
    }
    m.appendReplacement(sb, Matcher.quoteReplacement(replacement));
}
m.appendTail(sb);
System.out.println(sb.toString());