CODEWITHSUNDEEP
javaregexreplace
Thomas Nairn
Thomas Nairn

Reputation: 1226

Java String: Replacing string with multiple values

I'm currently building a config file that will replace a given string with multiple variables, I'm having a hard time explaining it so perhaps it would be best to show you what I mean:

The following method will be used with the String: Hello ~ and welcome to ~!

private static String REPLACE_CHAR = "~";

public static String parse(String key, String... inputs) {
    int cache = matchCache.get(key, -1);
    String value = customConfig.getString(key);
    if (cache == -1) {
        cache = StringUtils.countMatches(value, REPLACE_CHAR);
        matchCache.put(key, cache);
    }
    for (int i = 0; i < cache; i++) {
        value = value.replaceFirst(REPLACE_CHAR, inputs[i]);
    }
    return value;
}

what would be the fastest way to replace ~ with the first input, then move to the second ~ and so on...

Now the main reason I haven't used someone else's code: Ideally I'd like to create a List of different replaceable characters which will in turn replace the variable automatically, so in this same code I'm able to give it no inputs but it will check the List for replaceable characters and perform a method such as getYourName() This list does not need to be checked every time so a pattern may still be compiled?

I'm doing this to learn as much as for efficiency, I lack in ability when it comes to regex!

Upvotes: 4

Views: 2680

Answers (1)

Alex
Alex

Reputation: 25613

If you're looking for efficiency you can instantiate a Matcher using a regular expression, and then use the find() method to find occurrences, appending a replacement for each occurrence into a StringBuffer.

private Matcher matcher = Pattern.compile("([~])").matcher("");

public String parse(String key, String... inputs) {
    String value = customConfig.getString(key);
    matcher.reset(value);
    StringBuffer sb = new StringBuffer();
    int i = 0;
    while (matcher.find()) {
      String text = matcher.group(1);
      matcher.appendReplacement(sb, inputs[i++]);
    }
    matcher.appendTail(sb);
    return sb.toString();
}

System.out.println(parse("foo", "T F C", "James Bond"));
// prints "Hello T F C, my name is James Bond" 
// if customConfig.getString("foo") returns "Hello ~, my name is ~"

This way you avoid the finding from beginning of the string during each loop involved in String.replaceFirst. But you can still cache the number of ~ found if you want to verify that the length of input[] does equal to it.

The sample above does ignore the fact that the correct number of entries are stored in inputs[].

Runnable sample can be found here: http://ideone.com/QfE03a

Upvotes: 2

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