In Java HashMap is a very important and most used concept. It is mostly used in enterprise-level coding to mapping. Also, it is used in e-commerce applications to map orders with customers.
Map is a class of collection in Java which is used to store data in Key & Value pairs. In this tutorial we will learn the implementation of HashMap in Java.
HashMap Program In Java
import java.util.HashMap;
import java.util.Map;
public class Main{
public static void main(String[] args){
HashMap
map.put(“a”, 10);
map.put(“b”, 30);
map.put(“c”, 20);
System.out.println(map);
if (map.containsKey(“mno”))
{
Integer a = map.get(“mno”);
System.out.println(“value for key \”mno\” is:- ” + a);
}
map.clear();
print(map);
}
public static void print(Map
if (map.isEmpty()){
System.out.println(“map is empty”);
}
else{
System.out.println(map);
}
}
}
Now lets see
What is HashMap and its features in details.
HashMap is a part of Java’s collection framework that provides the implementation of the Map interface. HashMaps stores the data in key-value pairs. Each key has some value to print the value we fetch values from the key of HashMap and then print it.
HashMap uses a Hashing technique to converting a larger String to a smaller and store it into key-value pair.
Various features of HashMap in Java.
- Features of HashMap
- HashMap is available in the util package of Java.
- HashMap extends an abstract class AbstractMap.
- We cannot store duplicate keys in HashMap but we can store duplicate values.
- HashMap can have only one null key but can have multiple null values.
- Performance of Java HashMap
Performance of HashMap Depends upon Intial Capacity and Load Factor:
Initial Capacity: Capacity means size of the buckets which is declared when HashMap instance is created.
Load Factor: The Load Factor allowed to do Rehashing. Rehashing is basically a process to increase the capacity of HashMap.
HashMap Constructors
- HashMap()
- HashMap(int initial capacity)
- HashMap(int initial capacity, float load factor)
- HashMap(Map map)