Filter Integers From List of Strings

Filter only the integer values from a List and return them as a new list.

 List<String> list = Arrays.asList("10", "abc", "25", "xyz", "100", "-123");

 public static List<Integer> getIntegersFromList(List<String> list){

     return list.stream()
             .filter(s -> s.matches("-?\\d+"))
             .map(Integer::valueOf)
             .collect(Collectors.toList());
 }

 // Result:  [10, 25, 100, -123]

Explanation

1. stream() → converts list into stream
2. filter() → keeps only numeric strings
3. matches("-?\\d+") → regex for integer numbers
4. map(Integer::valueOf) → converts String → Integer
5. collect() → converts stream back to list

Regex meaning:

Pattern	Meaning
-?	optional negative sign
\d+	one or more digits

---

Using Try-Catch

Regex sometimes fails with edge cases.
A safer approach is try parsing.

public static List<Integer> getIntegersFromListUsingParseInt(List<String> list) {

    return list.stream().map(s -> {
        try {
            return Integer.parseInt(s);
        } catch (NumberFormatException e) {
            return null;
        }
    }).filter(Objects::nonNull).toList();
}

Why this approach is better

• Handles parsing exactly like Java does
• Avoids regex mistakes
• Preferred in backend systems