replace String with another in java using regular Expression

Question

In Java, I have to wrap a string value to another using RegEx and function replace.

Example #1: What will replace "123C5" (5 characters) with "*****"?

Example #2: What will replace "12354CF5214" (11 characters) with "*******5214"? replace only the first 7 characters

Currently, i am using this function but i need to optimize it :

public  String getMaskedValue(String value) {

    String maskedRes = "";
    if (value!=null && !value.isEmpty()) {
        maskedRes = value.trim();
        if (maskedRes.length() <= 5) {
            return maskedRes.replaceAll(value, "$1*");
        } else if (value.length() == 11) {
            return maskedRes.replace(value.substring(0, 7), "$1*");
        }
    }
    return maskedRes;
}

can anyone help me please ? thank you for advanced

Why use regexp at all? Substring the text and prepend the "******". Also, you should really explain WHY you need to optimize it, and in which way (execution speed? lines of code?), as the current version is not that bad. — SJuan76
– SJuan76, Commented Apr 22, 2020 at 12:12

Wiktor Stribiżew · Accepted Answer · 2020-04-22 12:13:43Z

2

You may use a constrained-width lookbehind solution like

public static String getMaskedValue(String value) {
    return value.replaceAll("(?<=^.{0,6}).", "*");
}

See the Java demo online.

The (?<=^.{0,6}). pattern matches any char (but a line break char, with .) that is preceded with 0 to 6 chars at the start of the string.

A note on the use of lookbehinds in Java regexps:

✽ Java accepts quantifiers within lookbehind, as long as the length of the matching strings falls within a pre-determined range. For instance, (?<=cats?) is valid because it can only match strings of three or four characters. Likewise, (?<=A{1,10}) is valid.

answered Apr 22, 2020 at 12:13

Wiktor Stribiżew

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