| // Copyright 2010 The Apache Software Foundation |
| // |
| // 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 org.apache.tapestry5.func; |
| |
| import java.util.Collections; |
| import java.util.Comparator; |
| import java.util.List; |
| import java.util.Set; |
| |
| /** |
| * An implementation of {@link Flow} for empty flows. This allows for some easy optimizations. |
| * |
| * @since 5.2.0 |
| */ |
| class EmptyFlow<T> extends AbstractFlow<T> |
| { |
| @Override |
| public T first() |
| { |
| return null; |
| } |
| |
| @Override |
| public boolean isEmpty() |
| { |
| return true; |
| } |
| |
| @Override |
| public Flow<T> rest() |
| { |
| return this; |
| } |
| |
| /** Does nothing; returns this empty list. */ |
| @Override |
| public Flow<T> each(Worker<? super T> worker) |
| { |
| return this; |
| } |
| |
| /** Does nothing; returns this empty list. */ |
| @Override |
| public Flow<T> filter(Predicate<? super T> predicate) |
| { |
| return this; |
| } |
| |
| /** Does nothing; returns this empty list. */ |
| @Override |
| public Flow<T> remove(Predicate<? super T> predicate) |
| { |
| return this; |
| } |
| |
| /** Does nothing; returns this empty list (as a Flow<X>). */ |
| @Override |
| public <X> Flow<X> map(Mapper<T, X> mapper) |
| { |
| return F.emptyFlow(); |
| } |
| |
| /** Does nothing; returns the initial value. */ |
| @Override |
| public <A> A reduce(Reducer<A, T> reducer, A initial) |
| { |
| return initial; |
| } |
| |
| /** Does nothing; returns this empty list. */ |
| @Override |
| public Flow<T> reverse() |
| { |
| return this; |
| } |
| |
| /** Does nothing; returns this empty list. */ |
| @Override |
| public Flow<T> sort() |
| { |
| return this; |
| } |
| |
| /** Does nothing; returns this empty list. */ |
| @Override |
| public Flow<T> sort(Comparator<T> comparator) |
| { |
| return this; |
| } |
| |
| /** Returns the empty list. */ |
| @Override |
| public List<T> toList() |
| { |
| return Collections.emptyList(); |
| } |
| |
| /** Returns the other list (i.e. empty ++ other == other). */ |
| @Override |
| @SuppressWarnings("unchecked") |
| public Flow<T> concat(Flow<? extends T> other) |
| { |
| return (Flow<T>) other; |
| } |
| |
| @Override |
| public <X> Flow<X> mapcat(Mapper<T, Flow<X>> mapper) |
| { |
| return F.emptyFlow(); |
| } |
| |
| @Override |
| public int count() |
| { |
| return 0; |
| } |
| |
| @Override |
| public Flow<T> take(int length) |
| { |
| return this; |
| } |
| |
| @Override |
| public Flow<T> drop(int length) |
| { |
| return this; |
| } |
| |
| @Override |
| public Set<T> toSet() |
| { |
| return Collections.emptySet(); |
| } |
| |
| @Override |
| public Flow<T> removeNulls() |
| { |
| return this; |
| } |
| } |