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package org.checkerframework.checker.nullness;

import java.util.NoSuchElementException;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
import org.checkerframework.checker.nullness.qual.EnsuresNonNullIf;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Utility class for the Nullness Checker, providing every method in {@link java.util.Optional}, but
 * written for possibly-null references rather than for the {@code Optional} type.
 *
 * 

To avoid the need to write the {@code Opt} class name at invocation sites, do: * *

import static org.checkerframework.checker.nullness.Opt.orElse;
* * or * *
import static org.checkerframework.checker.nullness.Opt.*;
* *

Runtime Dependency * *

Please note that using this class introduces a runtime dependency. This means that you need to * distribute (or link to) {@code checker-qual.jar}, along with your binaries. * *

To eliminate this dependency, you can simply copy this class into your own project. * * @see java.util.Optional */ public final class Opt { /** The Opt class cannot be instantiated. */ private Opt() { throw new AssertionError("shouldn't be instantiated"); } /** * If primary is non-null, returns it, otherwise throws NoSuchElementException. * * @param primary a non-null value to return * @return {@code primary} if it is non-null * @throws NoSuchElementException if primary is null * @see java.util.Optional#get() */ // `primary` is @NonNull; otherwise, the method could throw an exception. public static T get(T primary) { if (primary == null) { throw new NoSuchElementException("No value present"); } return primary; } /** * Returns true if primary is non-null, false if primary is null. * * @see java.util.Optional#isPresent() */ @EnsuresNonNullIf(expression = "#1", result = true) public static boolean isPresent(@Nullable Object primary) { return primary != null; } /** * If primary is non-null, invoke the specified consumer with the value, otherwise do nothing. * * @see java.util.Optional#ifPresent(Consumer) */ public static void ifPresent(T primary, Consumer<@NonNull ? super @NonNull T> consumer) { if (primary != null) { consumer.accept(primary); } } /** * If primary is non-null, and its value matches the given predicate, return the value. If * primary is null or its non-null value does not match the predicate, return null. * * @see java.util.Optional#filter(Predicate) */ public static @Nullable T filter( T primary, Predicate<@NonNull ? super @NonNull T> predicate) { if (primary == null) { return null; } else { return predicate.test(primary) ? primary : null; } } /** * If primary is non-null, apply the provided mapping function to it and return the result. If * primary is null, return null. * * @see java.util.Optional#map(Function) */ public static @Nullable U map( T primary, Function<@NonNull ? super @NonNull T, ? extends U> mapper) { if (primary == null) { return null; } else { return mapper.apply(primary); } } // flatMap would have the same signature and implementation as map /** * Return primary if it is non-null. If primary is null, return other. * * @see java.util.Optional#orElse(Object) */ public static @NonNull T orElse(T primary, @NonNull T other) { return primary != null ? primary : other; } /** * Return primary if it is non-null. If primary is null, invoke {@code other} and return the * result of that invocation. * * @see java.util.Optional#orElseGet(Supplier) */ public static @NonNull T orElseGet(T primary, Supplier other) { return primary != null ? primary : other.get(); } /** * Return primary if it is non-null. If primary is null, throw an exception to be created by the * provided supplier. * * @see java.util.Optional#orElseThrow(Supplier) */ // `primary` is @NonNull; otherwise, the method could throw an exception. public static T orElseThrow( T primary, Supplier exceptionSupplier) throws X { if (primary != null) { return primary; } else { throw exceptionSupplier.get(); } } }





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