How Can I Implement an SQL-LIKE 'LIKE' Operator in Java Using Regular Expressions?

Implementing an SQL-Like 'LIKE' Operator in Java

In Java, implementing a comparator with the same semantics as the SQL 'LIKE' operator can be achieved using regular expressions. Regular expressions provide a powerful way to match character patterns.

Creating a Comparator Using Regular Expressions

To create a comparator that behaves like the 'LIKE' operator, we can use the following syntax:

public static boolean like(String str, String pattern) {
  Pattern p = Pattern.compile(pattern);
  Matcher m = p.matcher(str);
  return m.matches();
}

Here's how the regular expressions work for your specified examples:

• %ital% matches any string containing "ital" anywhere in it.
• %gi?a% matches any string containing "gi" followed by any single character, followed by "a", anywhere in it.
• digi% matches any string starting with "digi".

Evaluation Examples

Using the like method, you can evaluate your specified conditions as follows:

• like("digital", "%ital%") evaluates to true because "digital" contains "ital".
• like("digital", "%gi?a%") evaluates to true because "digital" contains "gia".
• like("digital", "digi%") evaluates to true because "digital" starts with "digi".
• like("digital", "�m%") evaluates to false because "digital" does not contain "cam".
• like("digital", "tal%") evaluates to false because "digital" does not start with "tal".

Matching Characters and Dot

For regular expressions:

• .* matches any number of any characters.
• . matches a single character.
• To match an actual dot, escape it as ..

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