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Difference between HashTable and ConcurrentHashMap in Java
Concurrent Hashmap is a class that was introduced in jdk1.5. Concurrent hash map applies locks only at bucket level called fragment while adding or updating the map. So, a concurrent hash map allows concurrent read and write operations to the map.
HashTable is a thread-safe legacy class introduced in the Jdk1.1. It is a base implementation of Map interface. It doesn't allow null keys and values. It is synchronized in nature so two different threads can’t access simultaneously. Hashtable does not maintain any order.
| Sr. No. | Key | HashTable | ConcurrentHashMap |
|---|---|---|---|
1 | Basic | HashTable is a thread-safe legacy class introduced in the Jdk1.1 | ConcurrentHashmap is a class that was introduced in jdk1.5 |
2 | Locking | It applies lock on the entire collection | ConcurrentHashMap apply locks only at bucket level called fragment while adding or updating the map |
3 | Performance | It is slower than ConcurrentHashMap | It is better than HashTable |
4. | Null | It doesn't allow null key and value | It allows null key and value |
Example of Hashtable
import java.util.ArrayList;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.List;
import java.util.Map;
public class HashtableExample {
public static void main(String[] args) {
// create Hashtable
Hashtable map = new Hashtable();
map.put("HCL", "100");
map.put("DELL", "200");
map.put("IBM", "300");
// print the map
for (Map.Entry m : map.entrySet()) {
System.out.println(m.getKey() + " " + m.getValue());
}
}
}Example of ConcurrentHashMap
import java.util.ArrayList;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
public class ConcurrentHashMapExample {
public static void main(String[] args) {
// ConcurrentHashMap
Map myMap = new ConcurrentHashMap();
myMap.put("HCL", "1");
myMap.put("DELL", "1");
// print the map
for (Map.Entry m : map.entrySet()) {
System.out.println(m.getKey() + " " + m.getValue());
}
}
}
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