Introduction
Apache Commons Collections is an open source Java expansion library that provides many implementation of tool classes and data structures for processing sets.In its library, the implementation class of multiple MAP interfaces is also used to store the collection of key values on data.
The following will introduce some of the MAP implementation classes and brief descriptions in Apache Commons Collections.
1. Hashmap subclass
org.apache.commons.collections4.map.HashedMap
Hashedmap is a implementation of HashMap, which stores key value pairs through hash tables.It provides fast query and insert operations, and can achieve constant time search and modification.
Example code:
import org.apache.commons.collections4.MapIterator;
import org.apache.commons.collections4.map.HashedMap;
public class HashMapExample {
public static void main(String[] args) {
HashedMap<String, Integer> map = new HashedMap<>();
map.put("A", 1);
map.put("B", 2);
map.put("C", 3);
// Use Mapitrator to traverse map
MapIterator<String, Integer> iterator = map.mapIterator();
while (iterator.hasNext()) {
String key = iterator.next();
Integer value = iterator.getValue();
System.out.println("Key: " + key + ", Value: " + value);
}
}
}
2. Treemap subclass
org.apache.commons.collections4.map.TreeMap
TREEMAP is an orderly MAP based on red and black trees. It is sorted according to the natural order of the key (or through the order specified by the Comparator).This makes it suitable for scenarios that require orderly storage.
Example code:
import org.apache.commons.collections4.map.TreeMap;
public class TreeMapExample {
public static void main(String[] args) {
TreeMap<String, Integer> map = new TreeMap<>();
map.put("C", 3);
map.put("A", 1);
map.put("B", 2);
// Traversing an orderly map
for (String key : map.keySet()) {
Integer value = map.get(key);
System.out.println("Key: " + key + ", Value: " + value);
}
}
}
3. LinkedMap subclass
org.apache.commons.collections4.map.LinkedMap
LinkedMap is implemented through a two -way linked list.It can iterate in the order of the element, which is suitable for the scene that needs to be inserted.
Example code:
import org.apache.commons.collections4.map.LinkedMap;
public class LinkedMapExample {
public static void main(String[] args) {
LinkedMap<String, Integer> map = new LinkedMap<>();
map.put("A", 1);
map.put("B", 2);
map.put("C", 3);
// Traversing the map that keeps the insertion order
for (String key : map.keySet()) {
Integer value = map.get(key);
System.out.println("Key: " + key + ", Value: " + value);
}
}
}
The above introduces some of the commonly used MAP implementation classes and brief descriptions in Apache Commons Collections.These implementation classes are the expansion and enhancement of MAP in the Java standard library, which provides more functions and flexibility. In specific development, it can choose a appropriate implementation class according to the needs.
