// streams/OptionalFlatMap.java

// (c)2017 MindView LLC: see Copyright.txt

// We make no guarantees that this code is fit for any purpose.

// Visit http://OnJava8.com for more book information.

import java.util.*;

import java.util.stream.*;

import java.util.function.*;

class OptionalFlatMap {

static String[] elements = { "12", "", "23", "45" };

static Stream<String> testStream() {

return Arrays.stream(elements);

}

static void test(String descr,

Function<String, Optional<String>> func) {

System.out.println(" ---( " + descr + " )---");

for(int i = 0; i <= elements.length; i++) {

System.out.println(

testStream()

.skip(i)

.findFirst()

.flatMap(func));

}

}

public static void main(String[] args) {

test("Add brackets",

s -> Optional.of("[" + s + "]"));

test("Increment", s -> {

try {

return Optional.of(

Integer.parseInt(s) + 1 + "");

} catch(NumberFormatException e) {

return Optional.of(s);

}

});

test("Replace",

s -> Optional.of(s.replace("2", "9")));

test("Take last digit",

s -> Optional.of(s.length() > 0 ?

s.charAt(s.length() - 1) + ""

: s));

}

}

/* Output:

---( Add brackets )---

Optional[[12]]

Optional[[]]

Optional[[23]]

Optional[[45]]

Optional.empty

---( Increment )---

Optional[13]

Optional[]

Optional[24]

Optional[46]

Optional.empty

---( Replace )---

Optional[19]

Optional[]

Optional[93]

Optional[45]

Optional.empty

---( Take last digit )---

Optional[2]

Optional[]

Optional[3]

Optional[5]

Optional.empty

*/