001 // Copyright 2011 The Apache Software Foundation
002 //
003 // Licensed under the Apache License, Version 2.0 (the "License");
004 // you may not use this file except in compliance with the License.
005 // You may obtain a copy of the License at
006 //
007 // http://www.apache.org/licenses/LICENSE-2.0
008 //
009 // Unless required by applicable law or agreed to in writing, software
010 // distributed under the License is distributed on an "AS IS" BASIS,
011 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012 // See the License for the specific language governing permissions and
013 // limitations under the License.
014
015 package org.apache.tapestry5.func;
016
017 import java.util.Comparator;
018 import java.util.List;
019 import java.util.Set;
020
021 /**
022 * @param <T>
023 * the type of data in the flow
024 * @param <FT>
025 * the type of flow (either Flow<T> or ZippedFlow<Tuple<T, ?>)
026 * @since 5.3
027 */
028 public interface FlowOperations<T, FT> extends Iterable<T>
029 {
030 /**
031 * Filters values, keeping only values where the predicate is true, returning a new Flow with
032 * just the retained values.
033 */
034 FT filter(Predicate<? super T> predicate);
035
036 /**
037 * Removes values where the predicate returns true, returning a new Flow with just the remaining
038 * values.
039 */
040 FT remove(Predicate<? super T> predicate);
041
042 /**
043 * Applies the worker to each element in the Flow, then returns the flow for further behaviors.
044 * <p>
045 * Each is a non-lazy operation; it will fully realize the values of the Flow.
046 */
047 FT each(Worker<? super T> worker);
048
049 /**
050 * Converts the Flow into an unmodifiable list of values. This is a non-lazy operation that will
051 * fully realize the values of the Flow.
052 */
053 List<T> toList();
054
055 /**
056 * Converts the Flow into an unmodifiable set of values. This is a non-lazy operation that will
057 * fully realize the values of the Flow.
058 */
059 Set<T> toSet();
060
061 /** Returns a new flow with the same elements but in reverse order. */
062 FT reverse();
063
064 /**
065 * Returns true if the Flow contains no values. This <em>may</em> realize the first value in the
066 * Flow.
067 */
068 boolean isEmpty();
069
070 /**
071 * Returns the first element in the Flow. Returns null for empty flows, but remember that null
072 * is a valid element within a flow, so use {@link #isEmpty()} to determine if a flow is actually
073 * empty. The first element can be realized without realizing the full Flow.
074 */
075 T first();
076
077 /**
078 * Returns a new Flow containing all but the first element in this flow. If this flow has only a
079 * single element, or is empty, this will return an empty Flow.
080 */
081 FT rest();
082
083 /**
084 * Returns the number of values in this flow. This forces the realization of much of the flow
085 * (i.e., because each value will need to be passed through any {@link Predicate}s).
086 */
087 int count();
088
089 /**
090 * Sorts this flow using the comparator, forming a new flow. This is a non-lazy operation; it
091 * will fully realize the elements of the Flow.
092 */
093 FT sort(Comparator<T> comparator);
094
095 /**
096 * Returns a new flow containing just the first elements from this Flow.
097 *
098 * @param length
099 * maximum number of values in the Flow
100 */
101 FT take(int length);
102
103 /**
104 * Returns a new flow with the first elements omitted.
105 *
106 * @param length
107 * number of values to drop
108 */
109 FT drop(int length);
110
111 /**
112 * Returns a new Flow with the elements in the list appended to this Flow. This is a lazy
113 * operation.
114 */
115 FT concat(List<? extends T> list);
116
117 /**
118 * Applies a Reducer to the values of the Flow. The Reducer is passed the initial value
119 * and the first element from the Flow. The result is captured as the accumulator and passed
120 * to the Reducer with the next value from the Flow, and so on. The final accumulator
121 * value is returned. If the flow is empty, the initial value is returned.
122 * <p>
123 * Reducing is a non-lazy operation; it will fully realize the values of the Flow.
124 */
125 <A> A reduce(Reducer<A, T> reducer, A initial);
126
127 /**
128 * Removes null elements from the flow (null tuples from a ZippedFlow), leaving just the
129 * non-null elements. This is a lazy operation.
130 *
131 * @since 5.3
132 */
133 FT removeNulls();
134 }