Not able to remove substring that is variable from a string

Question

I want to remove everything except for Name. removeStart() and remove() don't seem to take variable as a parameter.

String tmpField  = '{!Contract.Name}';

String child = 'Contract';

tmpField = tmpField.removeStart('{!'); // Works

tmpField = tmpField.remove(child); // Doesn't seem to work - remove() or removeStart()

tmpField = tmpField.removeStart('.');

tmpField = tmpField.removeEnd('}');

Please let me know if any other ways to achieve that.

Answer 1

for this kind of task regex is the best instrument to use. Here is a link to test regex for your needs. You can also read an explanation for regex:

"(!Contract.)(.*)(?=})"
    1st Capturing Group (!Contract.)
        !Contract matches the characters !Contract literally (case sensitive)
        . matches any character (except for line terminators)
    2nd Capturing Group (.*)
        . matches any character (except for line terminators)
        * matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
    Positive Lookahead (?=})
Assert that the Regex below matches
    } matches the character } with index 12510 (7D16 or 1758) literally (case sensitive)

Apex:

String objectToMatch = 'Contract';
String stringToFind = '{!Contract.Name}';
Pattern pat = Pattern.compile('(!' + objectToMatch + '.)(.*)(?=})');
Matcher mat = pat.matcher(stringToFind);
if(mat.find()){
    System.debug(mat.group(2));
}

Debug:

|DEBUG|Name

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In this case, you can control for which object you need to parse a field from the input String.