com.hartveld.queryable.optional.None.java Source code

Introduction

Here is the source code for com.hartveld.queryable.optional.None.java

Source

/*
 * Copyright (c) 2013 David Hartveld
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package com.hartveld.queryable.optional;

import static com.google.common.base.Preconditions.checkNotNull;

import com.hartveld.queryable.Monad;
import com.hartveld.queryable.interactive.Enumerables;
import com.hartveld.queryable.interactive.Enumerator;
import com.hartveld.queryable.reactive.Observable;
import com.hartveld.queryable.reactive.Observables;
import java.util.NoSuchElementException;
import java.util.function.BinaryOperator;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;

public class None<T> implements Optional<T> {

    private static final None<?> SINGLETON = new None();

    static <T> None<T> instance() {
        return (None<T>) SINGLETON;
    }

    private None() {
    }

    @Override
    public boolean hasValue() {
        return false;
    }

    @Override
    public T getValue() throws NoSuchElementException {
        throw new NoSuchElementException("None has no value");
    }

    @Override
    public <R> Optional<R> flatMap(final Function<? super T, ? extends Monad<? extends R>> mapper) {
        return (Optional<R>) this;
    }

    @Override
    public <R> Optional<R> map(final Function<? super T, ? extends R> mapper) {
        return (Optional<R>) this;
    }

    @Override
    public Optional<T> reduce(final T identity, final BinaryOperator<T> accumulator) {
        checkNotNull(identity, "identity");

        return new Some<>(identity);
    }

    @Override
    public Optional<T> filter(final Predicate<? super T> predicate) {
        return this;
    }

    @Override
    public Optional<T> peek(final Consumer<? super T> consumer) {
        return this;
    }

    @Override
    public Enumerator<T> asEnumerator() {
        return Enumerables.<T>empty().iterator();
    }

    @Override
    public Observable<T> asObservable() {
        return Observables.empty();
    }

}