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// streams/Optionals.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.*;

public class Optionals {

static void basics(Optional<String> optString) {

if(optString.isPresent())

System.out.println(optString.get());

else

System.out.println("Nothing inside!");

}

static void ifPresent(Optional<String> optString) {

optString.ifPresent(System.out::println);

}

static void orElse(Optional<String> optString) {

System.out.println(optString.orElse("Nada"));

}

static void orElseGet(Optional<String> optString) {

System.out.println(

optString.orElseGet(() -> "Generated"));

}

static void orElseThrow(Optional<String> optString) {

try {

System.out.println(optString.orElseThrow(

() -> new Exception("Supplied")));

} catch(Exception e) {

System.out.println("Caught " + e);

}

}

static void test(String testName,

Consumer<Optional<String>> cos) {

System.out.println(" === " + testName + " === ");

cos.accept(Stream.of("Epithets").findFirst());

cos.accept(Stream.<String>empty().findFirst());

}

public static void main(String[] args) {

test("basics", Optionals::basics);

test("ifPresent", Optionals::ifPresent);

test("orElse", Optionals::orElse);

test("orElseGet", Optionals::orElseGet);

test("orElseThrow", Optionals::orElseThrow);

}

}

/* Output:

=== basics ===

Epithets

Nothing inside!

=== ifPresent ===

Epithets

=== orElse ===

Epithets

Nada

=== orElseGet ===

Epithets

Generated

=== orElseThrow ===

Epithets

Caught java.lang.Exception: Supplied

*/