StreamExample.java

import java.util.Arrays;
import java.util.stream.Stream;

public class StreamExample {
    public static void main(String... args){
        Stream.of("1", "Foo", "2", "Bar", "3")
                .filter(
                        str -> {
                            // To view stacktrace.
                            new Exception().printStackTrace();
                            return str.matches("\\d");
                        }
                )
                .forEach(System.out::println);
    }

}