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// streams/OptionalMap.java

// (c)2021 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 OptionalMap {

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

static Stream<String> testStream() {

return Arrays.stream(elements);

}

static void

test(String descr, Function<String, String> func) {

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

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

System.out.println(

testStream()

.skip(i)

.findFirst() // Produces an Optional

.map(func));

}

}

public static void main(String[] args) {

// If Optional is not empty, map() first extracts

// the contents which it then passes

// to the function:

test("Add brackets", s -> "[" + s + "]");

test("Increment", s -> {

try {

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

} catch(NumberFormatException e) {

return s;

}

});

test("Replace", s -> s.replace("2", "9"));

test("Take last digit", s -> s.length() > 0 ?

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

}

// After the function is finished, map() wraps the

// result in an Optional before returning it:

}

/* 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

*/