Java tutorial
/* * Copyright (c) 2016 Gridtec. All rights reserved. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package at.gridtec.lambda4j.function.bi; import at.gridtec.lambda4j.Lambda; import at.gridtec.lambda4j.consumer.ThrowableConsumer; import at.gridtec.lambda4j.consumer.bi.ThrowableBiConsumer; import at.gridtec.lambda4j.core.exception.ThrownByFunctionalInterfaceException; import at.gridtec.lambda4j.core.util.ThrowableUtils; import at.gridtec.lambda4j.function.ThrowableFunction; import org.apache.commons.lang3.tuple.Pair; import javax.annotation.Nonnegative; import javax.annotation.Nonnull; import javax.annotation.Nullable; import java.util.Map; import java.util.Objects; import java.util.Optional; import java.util.concurrent.ConcurrentHashMap; import java.util.function.BiFunction; import java.util.function.Function; /** * Represents an operation that accepts two input arguments and produces a * result which is able to throw any {@link Throwable}. * <p> * This is a {@link FunctionalInterface} whose functional method is {@link #applyThrows(Object, Object)}. * * @param <T> The type of the first argument to the function * @param <U> The type of the second argument to the function * @param <R> The type of return value from the function * @param <X> The type of the throwable to be thrown by this function * @apiNote This is a throwable JDK lambda. * @see ThrowableBiFunction */ @SuppressWarnings("unused") @FunctionalInterface public interface ThrowableBiFunction<T, U, R, X extends Throwable> extends Lambda, BiFunction<T, U, R> { /** * Constructs a {@link ThrowableBiFunction} based on a lambda expression or a method reference. Thereby the given * lambda expression or method reference is returned on an as-is basis to implicitly transform it to the desired * type. With this method, it is possible to ensure that correct type is used from lambda expression or method * reference. * * @param <T> The type of the first argument to the function * @param <U> The type of the second argument to the function * @param <R> The type of return value from the function * @param <X> The type of the throwable to be thrown by this function * @param expression A lambda expression or (typically) a method reference, e.g. {@code this::method} * @return A {@code ThrowableBiFunction} from given lambda expression or method reference. * @implNote This implementation allows the given argument to be {@code null}, but only if {@code null} given, * {@code null} will be returned. * @see <a href="https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html#syntax">Lambda * Expression</a> * @see <a href="https://docs.oracle.com/javase/tutorial/java/javaOO/methodreferences.html">Method Reference</a> */ static <T, U, R, X extends Throwable> ThrowableBiFunction<T, U, R, X> of( @Nullable final ThrowableBiFunction<T, U, R, X> expression) { return expression; } /** * Lifts a partial {@link ThrowableBiFunction} into a total {@link ThrowableBiFunction} that returns an {@link * Optional} result. * * @param <T> The type of the first argument to the function * @param <U> The type of the second argument to the function * @param <R> The type of return value from the function * @param <X> The type of the throwable to be thrown by this function * @param partial A function that is only defined for some values in its domain * @return A partial {@code ThrowableBiFunction} lifted into a total {@code ThrowableBiFunction} that returns an * {@code Optional} result. * @throws NullPointerException If given argument is {@code null} */ @Nonnull static <T, U, R, X extends Throwable> ThrowableBiFunction<T, U, Optional<R>, X> lift( @Nonnull final ThrowableBiFunction<? super T, ? super U, ? extends R, ? extends X> partial) { Objects.requireNonNull(partial); return (t, u) -> Optional.ofNullable(partial.applyThrows(t, u)); } /** * Calls the given {@link ThrowableBiFunction} with the given arguments and returns its result. * * @param <T> The type of the first argument to the function * @param <U> The type of the second argument to the function * @param <R> The type of return value from the function * @param <X> The type of the throwable to be thrown by this function * @param function The function to be called * @param t The first argument to the function * @param u The second argument to the function * @return The result from the given {@code ThrowableBiFunction}. * @throws NullPointerException If given argument is {@code null} * @throws X Any throwable from this functions action */ static <T, U, R, X extends Throwable> R call( @Nonnull final ThrowableBiFunction<? super T, ? super U, ? extends R, ? extends X> function, T t, U u) throws X { Objects.requireNonNull(function); return function.applyThrows(t, u); } /** * Creates a {@link ThrowableBiFunction} which uses the {@code first} parameter of this one as argument for the * given {@link ThrowableFunction}. * * @param <T> The type of the first argument to the function * @param <U> The type of the second argument to the function * @param <R> The type of return value from the function * @param <X> The type of the throwable to be thrown by this function * @param function The function which accepts the {@code first} parameter of this one * @return Creates a {@code ThrowableBiFunction} which uses the {@code first} parameter of this one as argument for * the given {@code ThrowableFunction}. * @throws NullPointerException If given argument is {@code null} */ @Nonnull static <T, U, R, X extends Throwable> ThrowableBiFunction<T, U, R, X> onlyFirst( @Nonnull final ThrowableFunction<? super T, ? extends R, ? extends X> function) { Objects.requireNonNull(function); return (t, u) -> function.applyThrows(t); } /** * Creates a {@link ThrowableBiFunction} which uses the {@code second} parameter of this one as argument for the * given {@link ThrowableFunction}. * * @param <T> The type of the first argument to the function * @param <U> The type of the second argument to the function * @param <R> The type of return value from the function * @param <X> The type of the throwable to be thrown by this function * @param function The function which accepts the {@code second} parameter of this one * @return Creates a {@code ThrowableBiFunction} which uses the {@code second} parameter of this one as argument for * the given {@code ThrowableFunction}. * @throws NullPointerException If given argument is {@code null} */ @Nonnull static <T, U, R, X extends Throwable> ThrowableBiFunction<T, U, R, X> onlySecond( @Nonnull final ThrowableFunction<? super U, ? extends R, ? extends X> function) { Objects.requireNonNull(function); return (t, u) -> function.applyThrows(u); } /** * Creates a {@link ThrowableBiFunction} which always returns a given value. * * @param <T> The type of the first argument to the function * @param <U> The type of the second argument to the function * @param <R> The type of return value from the function * @param <X> The type of the throwable to be thrown by this function * @param ret The return value for the constant * @return A {@code ThrowableBiFunction} which always returns a given value. */ @Nonnull static <T, U, R, X extends Throwable> ThrowableBiFunction<T, U, R, X> constant(R ret) { return (t, u) -> ret; } /** * Applies this function to the given arguments. * * @param t The first argument to the function * @param u The second argument to the function * @return The return value from the function, which is its result. * @throws X Any throwable from this functions action */ R applyThrows(T t, U u) throws X; /** * Applies this function to the given arguments. * * @param t The first argument to the function * @param u The second argument to the function * @return The return value from the function, which is its result. * @apiNote This method mainly exists to use this {@link ThrowableBiFunction} in JRE specific methods only accepting * {@link BiFunction}. If this function should be applied, then the {@link #applyThrows(Object, Object)} method * should be used. * @apiNote Overrides the {@link BiFunction#apply(Object, Object)} method by using a redefinition as default method. * This implementation calls the {@link #applyThrows(Object, Object)} method of this function and catches the * eventually thrown {@link Throwable} from it. If it is of type {@link RuntimeException} or {@link Error} it is * rethrown as is. Other {@code Throwable} types are wrapped in a {@link ThrownByFunctionalInterfaceException}. */ @Override default R apply(T t, U u) { // TODO: Remove commented code below /*try { return this.applyThrows(t, u); } catch (RuntimeException | Error e) { throw e; } catch (Throwable throwable) { throw new ThrownByFunctionalInterfaceException(throwable.getMessage(), throwable); }*/ return nest().apply(t, u); } /** * Applies this function to the given tuple. * * @param tuple The tuple to be applied to the function * @return The return value from the function, which is its result. * @throws NullPointerException If given argument is {@code null} * @throws X Any throwable from this functions action * @see org.apache.commons.lang3.tuple.Pair */ default R applyThrows(@Nonnull Pair<T, U> tuple) throws X { Objects.requireNonNull(tuple); return applyThrows(tuple.getLeft(), tuple.getRight()); } /** * Applies this function partially to some arguments of this one, producing a {@link ThrowableFunction} as result. * * @param t The first argument to this function used to partially apply this function * @return A {@code ThrowableFunction} that represents this function partially applied the some arguments. */ @Nonnull default ThrowableFunction<U, R, X> papplyThrows(T t) { return (u) -> this.applyThrows(t, u); } /** * Returns the number of arguments for this function. * * @return The number of arguments for this function. * @implSpec The default implementation always returns {@code 2}. */ @Nonnegative default int arity() { return 2; } /** * Returns a composed {@link ThrowableBiFunction} that first applies the {@code before} functions to its input, and * then applies this function to the result. * * @param <A> The type of the argument to the first given function, and of composed function * @param <B> The type of the argument to the second given function, and of composed function * @param before1 The first function to apply before this function is applied * @param before2 The second function to apply before this function is applied * @return A composed {@code ThrowableBiFunction} that first applies the {@code before} functions to its input, and * then applies this function to the result. * @throws NullPointerException If given argument is {@code null} * @implSpec The input argument of this method is able to handle every type. */ @Nonnull default <A, B> ThrowableBiFunction<A, B, R, X> compose( @Nonnull final ThrowableFunction<? super A, ? extends T, ? extends X> before1, @Nonnull final ThrowableFunction<? super B, ? extends U, ? extends X> before2) { Objects.requireNonNull(before1); Objects.requireNonNull(before2); return (a, b) -> applyThrows(before1.applyThrows(a), before2.applyThrows(b)); } /** * Returns a composed {@link ThrowableBiFunction} that first applies this function to its input, and then applies * the {@code after} function to the result. * * @param <S> The type of return value from the {@code after} function, and of the composed function * @param after The function to apply after this function is applied * @return A composed {@code ThrowableBiFunction} that first applies this function to its input, and then applies * the {@code after} function to the result. * @throws NullPointerException If given argument is {@code null} * @implSpec The input argument of this method is able to return every type. */ @Nonnull default <S> ThrowableBiFunction<T, U, S, X> andThen( @Nonnull final ThrowableFunction<? super R, ? extends S, ? extends X> after) { Objects.requireNonNull(after); return (t, u) -> after.applyThrows(applyThrows(t, u)); } /** * Returns a composed {@link ThrowableBiConsumer} that fist applies this function to its input, and then consumes * the result using the given {@link ThrowableConsumer}. * * @param consumer The operation which consumes the result from this operation * @return A composed {@code ThrowableBiConsumer} that first applies this function to its input, and then consumes * the result using the given {@code ThrowableConsumer}. * @throws NullPointerException If given argument is {@code null} */ @Nonnull default ThrowableBiConsumer<T, U, X> consume( @Nonnull final ThrowableConsumer<? super R, ? extends X> consumer) { Objects.requireNonNull(consumer); return (t, u) -> consumer.acceptThrows(applyThrows(t, u)); } /** * Returns a curried version of this function. * * @return A curried version of this function. */ @Nonnull default ThrowableFunction<T, ThrowableFunction<U, R, X>, X> curried() { return t -> u -> applyThrows(t, u); } /** * Returns a tupled version of this function. * * @return A tupled version of this function. */ @Nonnull default ThrowableFunction<Pair<T, U>, R, X> tupled() { return this::applyThrows; } /** * Returns a reversed version of this function. This may be useful in recursive context. * * @return A reversed version of this function. */ @Nonnull default ThrowableBiFunction<U, T, R, X> reversed() { return (u, t) -> applyThrows(t, u); } /** * Returns a memoized (caching) version of this {@link ThrowableBiFunction}. Whenever it is called, the mapping * between the input parameters and the return value is preserved in a cache, making subsequent calls returning the * memoized value instead of computing the return value again. * <p> * Unless the function and therefore the used cache will be garbage-collected, it will keep all memoized values * forever. * * @return A memoized (caching) version of this {@code ThrowableBiFunction}. * @implSpec This implementation does not allow the input parameters or return value to be {@code null} for the * resulting memoized function, as the cache used internally does not permit {@code null} keys or values. * @implNote The returned memoized function can be safely used concurrently from multiple threads which makes it * thread-safe. */ @Nonnull default ThrowableBiFunction<T, U, R, X> memoized() { if (isMemoized()) { return this; } else { final Map<Pair<T, U>, R> cache = new ConcurrentHashMap<>(); final Object lock = new Object(); return (ThrowableBiFunction<T, U, R, X> & Memoized) (t, u) -> { final R returnValue; synchronized (lock) { returnValue = cache.computeIfAbsent(Pair.of(t, u), ThrowableFunction.of(key -> applyThrows(key.getLeft(), key.getRight()))); } return returnValue; }; } } /** * Converts this function to an equal function, which ensures that its result is not * {@code null} using {@link Optional}. This method mainly exists to avoid unnecessary {@code NullPointerException}s * through referencing {@code null} from this function. * * @return An equal function, which ensures that its result is not {@code null}. * @deprecated Use {@code lift} method for lifting this function. */ @Deprecated @Nonnull default ThrowableBiFunction<T, U, Optional<R>, X> nonNull() { return (t, u) -> Optional.ofNullable(applyThrows(t, u)); } /** * Returns a composed {@link BiFunction2} that applies this function to its input and nests the thrown {@link * Throwable} from it. The {@code Throwable} is nested (wrapped) in a {@link ThrownByFunctionalInterfaceException}, * which is constructed from the thrown {@code Throwable}s message and the thrown {@code Throwable} itself. * * @return A composed {@link BiFunction2} that applies this function to its input and nests the thrown {@code * Throwable} from it. * @implNote If thrown {@code Throwable} is of type {@link Error} it is thrown as-is and thus not nested. * @see #nestWith(Function) * @see ThrownByFunctionalInterfaceException */ @Nonnull default BiFunction2<T, U, R> nest() { return nestWith(throwable -> new ThrownByFunctionalInterfaceException(throwable.getMessage(), throwable)); } /** * Returns a composed {@link BiFunction2} that applies this function to its input and nests the thrown {@link * Throwable} from it using {@code mapper} operation. Thereby {@code mapper} may modify the thrown {@code * Throwable}, regarding its implementation, and returns it nested (wrapped) in a {@link RuntimeException}. * * @param mapper The operation to map the thrown {@code Throwable} to {@code RuntimeException} * @return A composed {@link BiFunction2} that applies this function to its input and nests the thrown {@code * Throwable} from it using {@code mapper} operation. * @throws NullPointerException If given argument is {@code null} * @implNote If thrown {@code Throwable} is of type {@link Error} it is thrown as-is and thus not nested. * @see #nest() */ @Nonnull default BiFunction2<T, U, R> nestWith( @Nonnull final Function<? super Throwable, ? extends RuntimeException> mapper) { return recover(throwable -> { throw mapper.apply(throwable); }); } /** * Returns a composed {@link BiFunction2} that applies this function to its input and sneakily throws the * thrown {@link Throwable} from it, if it is not of type {@link RuntimeException} or {@link Error}. This means that * each throwable thrown from the returned composed function behaves exactly the same as an <em>unchecked</em> * throwable does. As a result, there is no need to handle the throwable of this function in the returned composed * function by either wrapping it in an <em>unchecked</em> throwable or to declare it in the {@code throws} clause, * as it would be done in a non sneaky throwing function. * <p> * What sneaky throwing simply does, is to fake out the compiler and thus it bypasses the principle of * <em>checked</em> throwables. On the JVM (class file) level, all throwables, checked or not, can be thrown * regardless of the {@code throws} clause of methods, which is why this works at all. * <p> * However, when using this method to get a sneaky throwing function variant of this throwable function, the * following advantages, disadvantages and limitations will apply: * <p> * If the calling-code is to handle the sneakily thrown throwable, it is required to add it to the {@code throws} * clause of the method that applies the returned composed function. The compiler will not force the declaration in * the {@code throws} clause anymore. * <p> * If the calling-code already handles the sneakily thrown throwable, the compiler requires it to be added to the * {@code throws} clause of the method that applies the returned composed function. If not added, the compiler will * error that the caught throwable is never thrown in the corresponding {@code try} block. * <p> * If the returned composed function is directly surrounded by a {@code try}-{@code catch} block to catch the * sneakily thrown throwable from it, the compiler will error that the caught throwable is never thrown in the * corresponding {@code try} block. * <p> * In any case, if the throwable is not added to the to the {@code throws} clause of the method that applies the * returned composed function, the calling-code won't be able to catch the throwable by name. It will bubble and * probably be caught in some {@code catch} statement, catching a base type such as {@code try { ... } * catch(RuntimeException e) { ... }} or {@code try { ... } catch(Exception e) { ... }}, but perhaps this is * intended. * <p> * When the called code never throws the specific throwable that it declares, it should obviously be omitted. For * example: {@code new String(byteArr, "UTF-8") throws UnsupportedEncodingException}, but {@code UTF-8} is * guaranteed by the Java specification to be always present. Here, the {@code throws} declaration is a nuisance and * any solution to silence it with minimal boilerplate is welcome. The throwable should therefore be omitted in the * {@code throws} clause of the method that applies the returned composed function. * <p> * With all that mentioned, the following example will demonstrate this methods correct use: * <pre>{@code * // when called with illegal value ClassNotFoundException is thrown * public Class<?> sneakyThrowingFunctionalInterface(final String className) throws ClassNotFoundException { * return ThrowableFunction.of(Class::forName) // create the correct throwable functional interface * .sneakyThrow() // create a non-throwable variant which is able to sneaky throw (this method) * .apply(className); // apply non-throwable variant -> may sneaky throw a throwable * } * * // call the the method which surround the sneaky throwing functional interface * public void callingMethod() { * try { * final Class<?> clazz = sneakyThrowingFunctionalInterface("some illegal class name"); * // ... do something with clazz ... * } catch(ClassNotFoundException e) { * // ... do something with e ... * } * } * }</pre> * In conclusion, this somewhat contentious ability should be used carefully, of course, with the advantages, * disadvantages and limitations described above kept in mind. * * @return A composed {@link BiFunction2} that applies this function to its input and sneakily throws the thrown * {@link Throwable} from it, unless it is of type {@link RuntimeException} or {@link Error}. * @implNote If thrown {@link Throwable} is of type {@link RuntimeException} or {@link Error}, it is thrown as-is * and thus not sneakily thrown. */ @Nonnull default BiFunction2<T, U, R> sneakyThrow() { return (t, u) -> { try { return this.applyThrows(t, u); } catch (RuntimeException | Error e) { throw e; } catch (Throwable throwable) { throw ThrowableUtils.sneakyThrow(throwable); } }; } /** * Returns a composed {@link BiFunction2} that first applies this function to its input, and then applies the {@code * recover} operation if a {@link Throwable} is thrown from this one. The {@code recover} operation is represented * by a curried operation which is called with throwable information and same arguments of this function. * * @param recover The operation to apply if this function throws a {@code Throwable} * @return A composed {@link BiFunction2} that first applies this function to its input, and then applies the {@code * recover} operation if a {@code Throwable} is thrown from this one. * @throws NullPointerException If given argument or the returned enclosing function is {@code null} * @implSpec The implementation checks that the returned enclosing function from {@code recover} operation is not * {@code null}. If it is, then a {@link NullPointerException} with appropriate message is thrown. * @implNote If thrown {@code Throwable} is of type {@link Error}, it is thrown as-is and thus not passed to {@code * recover} operation. */ @Nonnull default BiFunction2<T, U, R> recover( @Nonnull final Function<? super Throwable, ? extends BiFunction<? super T, ? super U, ? extends R>> recover) { Objects.requireNonNull(recover); return (t, u) -> { try { return this.applyThrows(t, u); } catch (Error e) { throw e; } catch (Throwable throwable) { final BiFunction<? super T, ? super U, ? extends R> function = recover.apply(throwable); Objects.requireNonNull(function, () -> "recover returned null for " + throwable.getClass() + ": " + throwable.getMessage()); return function.apply(t, u); } }; } }