com.thebuzzmedia.exiftool.commons.iterables.Collections Maven / Gradle / Ivy
/**
* Copyright 2011 The Buzz Media, LLC
* Copyright 2015 Mickael Jeanroy
*
* 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 com.thebuzzmedia.exiftool.commons.iterables;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
/**
* Static Collection Utilities.
*/
public final class Collections {
// Ensure non instantiation.
private Collections() {
}
/**
* Check if collection is empty ({@code null} or empty).
*
* @param values Collection of values.
* @param Type of element in collection.
* @return True if collection is empty (null or empty), false otherwise.
*/
public static boolean isEmpty(Collection values) {
return values == null || values.isEmpty();
}
/**
* Get size of collection.
* If collection is empty (null or empty), zero will be returned.
*
* @param values Collection of values.
* @param Type of element in collection.
* @return Size of collection.
*/
public static int size(Collection values) {
return isEmpty(values) ? 0 : values.size();
}
/**
* Join elements of collection to a final string.
* If collection is empty (null or empty), an empty string is returned.
*
* @param values Collection of values.
* @param separator Separator, use to separate each elements.
* @param Type of element in collection.
* @return Final string.
*/
public static String join(Collection values, String separator) {
if (isEmpty(values)) {
return "";
}
Iterator it = values.iterator();
StringBuilder sb = new StringBuilder();
sb.append(it.next());
while (it.hasNext()) {
sb.append(separator).append(it.next());
}
return sb.toString();
}
/**
* Map list of inputs to a new list of outputs.
*
* @param inputs Input list.
* @param mapper Mapper used to transform inputs.
* @param Type of input.
* @param Type of output.
* @return New list of outputs.
*/
public static List map(List inputs, Mapper mapper) {
List outputs = new ArrayList(inputs.size());
for (T input : inputs) {
U output = mapper.map(input);
outputs.add(output);
}
return outputs;
}
/**
* Index list of inputs by result of mapper function.
*
* @param inputs List of inputs.
* @param indexer Mapper function.
* @param Type of input.
* @param Type of index keys.
* @return Map of key (result of mapper function) with values (inputs).
*/
public static Map indexBy(Iterable inputs, Mapper indexer) {
Map index = new HashMap();
for (T input : inputs) {
U output = indexer.map(input);
index.put(output, input);
}
return index;
}
}