How can I replace two strings in a way that one does not end up replacing the other?

Let's say that I have the following code:

String word1 = "bar";
String word2 = "foo";
String story = "Once upon a time, there was a foo and a bar."
story = story.replace("foo", word1);
story = story.replace("bar", word2);

After this code runs, the value of story will be "Once upon a time, there was a foo and a foo."

A similar issue occurs if I replaced them in the opposite order:

String word1 = "bar";
String word2 = "foo";
String story = "Once upon a time, there was a foo and a bar."
story = story.replace("bar", word2);
story = story.replace("foo", word1);

The value of story will be "Once upon a time, there was a bar and a bar."

My goal is to turn story into "Once upon a time, there was a bar and a foo." How could I accomplish that?

Solution 1:

Use the replaceEach() method from Apache Commons StringUtils:

StringUtils.replaceEach(story, new String[]{"foo", "bar"}, new String[]{"bar", "foo"})

Solution 2:

You use an intermediate value (which is not yet present in the sentence).

story = story.replace("foo", "lala");
story = story.replace("bar", "foo");
story = story.replace("lala", "bar");

As a response to criticism: if you use a large enough uncommon string like zq515sqdqs5d5sq1dqs4d1q5dqqé"&é5d4sqjshsjddjhodfqsqc, nvùq^µù;d&€sdq: d: ;)àçàçlala and use that, it is unlikely to the point where I won't even debate it that a user will ever enter this. The only way to know whether a user will is by knowing the source code and at that point you're with a whole other level of worries.

Yes, maybe there are fancy regex ways. I prefer something readable that I know will not break out on me either.

Also reiterating the excellent advise given by @David Conrad in the comments:

Don't use some string cleverly (stupidly) chosen to be unlikely. Use characters from the Unicode Private Use Area, U+E000..U+F8FF. Remove any such characters first, since they shouldn't legitimately be in the input (they only have application-specific meaning within some application), then use them as placeholders when replacing.

Solution 3:

You can try something like this, using Matcher#appendReplacement and Matcher#appendTail:

String word1 = "bar";
String word2 = "foo";
String story = "Once upon a time, there was a foo and a bar.";

Pattern p = Pattern.compile("foo|bar");
Matcher m = p.matcher(story);
StringBuffer sb = new StringBuffer();
while (m.find()) {
    /* do the swap... */
    switch (m.group()) {
    case "foo":
        m.appendReplacement(sb, word1);
        break;
    case "bar":
        m.appendReplacement(sb, word2);
        break;
    default:
        /* error */
        break;
    }
}
m.appendTail(sb);

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

Once upon a time, there was a bar and a foo.