import java.util.ArrayList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
class Ideone {
    public static void main(String args[]) {
        final String sample = "123 45 678b a90";
        final Pattern pattern = Pattern.compile("\\b\\d+\\b");
        final Matcher matcher = pattern.matcher(sample);
        final ArrayList<String> results = new ArrayList<>();
        while (matcher.find()) {
            results.add(matcher.group());
        }
        System.out.println(results);
    }
}

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