74 lines
1.6 KiB
Java
74 lines
1.6 KiB
Java
// streams/OptionalFlatMap.java
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// (c)2021 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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import java.util.*;
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import java.util.stream.*;
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import java.util.function.*;
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class OptionalFlatMap {
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static String[] elements = { "12", "", "23", "45" };
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static Stream<String> testStream() {
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return Arrays.stream(elements);
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}
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static void test(String descr,
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Function<String, Optional<String>> func) {
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System.out.println(" ---( " + descr + " )---");
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for(int i = 0; i <= elements.length; i++) {
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System.out.println(
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testStream()
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.skip(i)
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.findFirst()
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.flatMap(func));
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}
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}
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public static void main(String[] args) {
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test("Add brackets",
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s -> Optional.of("[" + s + "]"));
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test("Increment", s -> {
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try {
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return Optional.of(
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Integer.parseInt(s) + 1 + "");
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} catch(NumberFormatException e) {
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return Optional.of(s);
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}
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});
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test("Replace",
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s -> Optional.of(s.replace("2", "9")));
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test("Take last digit",
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s -> Optional.of(s.length() > 0 ?
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s.charAt(s.length() - 1) + ""
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: s));
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}
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}
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/* Output:
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---( Add brackets )---
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Optional[[12]]
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Optional[[]]
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Optional[[23]]
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Optional[[45]]
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Optional.empty
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---( Increment )---
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Optional[13]
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Optional[]
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Optional[24]
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Optional[46]
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Optional.empty
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---( Replace )---
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Optional[19]
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Optional[]
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Optional[93]
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Optional[45]
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Optional.empty
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---( Take last digit )---
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Optional[2]
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Optional[]
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Optional[3]
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Optional[5]
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Optional.empty
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*/
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