49 lines
1.4 KiB
Java
49 lines
1.4 KiB
Java
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// enumerations/SealedPatternMatch.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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// {NewFeature} Preview in JDK 17
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// Compile with javac flags:
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// --enable-preview --source 17
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// Run with java flag: --enable-preview
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import java.util.*;
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sealed interface Transport {};
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record Bicycle(String id) implements Transport {};
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record Glider(int size) implements Transport {};
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record Surfboard(double weight) implements Transport {};
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// If you uncomment this:
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// record Skis(int length) implements Transport {};
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// You get an error: "the switch expression
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// does not cover all possible input values"
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public class SealedPatternMatch {
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static String exhaustive(Transport t) {
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return switch(t) {
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case Bicycle b -> "Bicycle " + b.id();
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case Glider g -> "Glider " + g.size();
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case Surfboard s -> "Surfboard " + s.weight();
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};
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}
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public static void main(String[] args) {
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List.of(
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new Bicycle("Bob"),
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new Glider(65),
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new Surfboard(6.4)
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).forEach(
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t -> System.out.println(exhaustive(t))
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);
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try {
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exhaustive(null); // Always possible! // [1]
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} catch(NullPointerException e) {
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System.out.println("Not exhaustive: " + e);
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}
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}
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}
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/* Output:
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Bicycle Bob
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Glider 65
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Surfboard 6.4
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Not exhaustive: java.lang.NullPointerException
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*/
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