Apache Commons Collections Framework Overview
Apache Commons Collections Framework Overview
Apache Commons Collections is an open source Java class library that provides a collection of expansion, operation and practical functions on the collection.It expands the Java set framework, which contains many useful data structures and algorithms to simplify the work of developers to handle collection.
Apache Commons Collections provides five main functional modules:
1. Collection Extensions: This module provides some extended set classes such as Bidimap (two -way mapping), Multimap (multi -value mapping) and TransformedCollection.These classes provide more functions and flexibility to meet the needs of various collection processing.
Example code:
// Create a two -way mapping
BidiMap<String, String> bidiMap = new DualHashBidiMap<>();
bidiMap.put("key1", "value1");
bidiMap.put("key2", "value2");
// Obtain the corresponding key through the value
String key = bidiMap.getKey("value1");
System.out.println (key); // Output: key1
2. Collection Utilities: This module contains a series of practical methods for operation and processing collection.For example, you can use the method in this module to quickly create a collection of collection, eliminate the repetitive elements in the set, and convert the collection into an array.
Example code:
// Create a collection of only collection
List<String> names = CollectionUtils.unmodifiableList(new ArrayList<>(Arrays.asList("John", "Jane", "Alice")));
// Convert the collection to a array
String[] namesArray = CollectionUtils.toArray(names);
3. Sorting: This module provides some algorithms and tools that can sort the set.These tools support custom comparators and can be applied to various collection types.
Example code:
// Sort the list
List<Integer> numbers = new ArrayList<>(Arrays.asList(3, 1, 4, 1, 5, 9, 2));
Comparator<Integer> comparator = Comparator.naturalOrder();
Collections.sort(numbers, comparator);
System.out.println (numbers); // Output: [1, 1, 2, 3, 4, 5, 9]
4. Transformers: This module provides some tool classes for converting collection elements.These tools can be used to convert the elements in the collection, filtering, and combination.
Example code:
// Convert the string elements in the collection to uppercase
List<String> fruits = new ArrayList<>(Arrays.asList("apple", "banana", "orange"));
Transformer<String, String> transformer = new Transformer<String, String>() {
@Override
public String transform(String input) {
return input.toUpperCase();
}
};
CollectionUtils.transform(fruits, transformer);
System.out.println (from); // Output: [Apple, Banana, Orange]
5. Iteration: This module provides some tool classes for iterative set elements.By using these tools, you can easily traverse and operate collection elements.
Example code:
// Traversing the key value in the map
Map<String, Integer> grades = new HashMap<>();
grades.put("John", 90);
grades.put("Alice", 85);
grades.put("Bob", 95);
Iterator<Map.Entry<String, Integer>> iterator = grades.entrySet().iterator();
while (iterator.hasNext()) {
Map.Entry<String, Integer> entry = iterator.next();
System.out.println(entry.getKey() + ": " + entry.getValue());
}
Summarize:
Apache Commons Collections is a powerful Java class library that provides many useful collection processing tools and algorithms.Whether it is extended Java collection, or sorting, conversion, etc., Apache Commons Collections can provide convenient and convenient solutions.By using Apache Commons Collections, developers can handle and operate collection more efficiently.
