64 lines
2.1 KiB
Java
64 lines
2.1 KiB
Java
package optional;
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import java.io.*;
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import java.nio.charset.*;
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import java.nio.file.*;
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import java.util.*;
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public class OptionalTest
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{
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public static void main(String[] args) throws IOException
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{
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String contents = new String(Files.readAllBytes(
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Paths.get("../gutenberg/alice30.txt")), StandardCharsets.UTF_8);
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List<String> wordList = Arrays.asList(contents.split("\\PL+"));
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Optional<String> optionalValue = wordList.stream()
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.filter(s -> s.contains("fred"))
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.findFirst();
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System.out.println(optionalValue.orElse("No word") + " contains fred");
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Optional<String> optionalString = Optional.empty();
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String result = optionalString.orElse("N/A");
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System.out.println("result: " + result);
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result = optionalString.orElseGet(() -> Locale.getDefault().getDisplayName());
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System.out.println("result: " + result);
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try
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{
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result = optionalString.orElseThrow(IllegalStateException::new);
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System.out.println("result: " + result);
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}
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catch (Throwable t)
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{
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t.printStackTrace();
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}
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optionalValue = wordList.stream()
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.filter(s -> s.contains("red"))
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.findFirst();
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optionalValue.ifPresent(s -> System.out.println(s + " contains red"));
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Set<String> results = new HashSet<>();
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optionalValue.ifPresent(results::add);
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Optional<Boolean> added = optionalValue.map(results::add);
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System.out.println(added);
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System.out.println(inverse(4.0).flatMap(OptionalTest::squareRoot));
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System.out.println(inverse(-1.0).flatMap(OptionalTest::squareRoot));
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System.out.println(inverse(0.0).flatMap(OptionalTest::squareRoot));
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Optional<Double> result2 = Optional.of(-4.0)
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.flatMap(OptionalTest::inverse).flatMap(OptionalTest::squareRoot);
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System.out.println(result2);
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}
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public static Optional<Double> inverse(Double x)
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{
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return x == 0 ? Optional.empty() : Optional.of(1 / x);
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}
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public static Optional<Double> squareRoot(Double x)
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{
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return x < 0 ? Optional.empty() : Optional.of(Math.sqrt(x));
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}
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}
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