Java HashMap put() usage and example

Java HashMap Methods

The Java HashMap put() method adds the specified item (key/Value mapping) inserted into the HashMap.

The syntax of the put() method is:

hashmap.put(K key, V value)

put() parameters

The HashMap put() method can take two parameters:

• key - The specified value is mapped to the key

• value　 - Value mapped using the specified key
  

put() return value

• If the key is already associated with any value, it returns the previously associated value

• If the key is not associated with any value, it returns null
  

Note:If the key was previously associated with a null value, this method will also return null.

Example1: Java HashMap put()

import java.util.HashMap;
class Main {
　　public static void main(String[] args) {
　　　　//　Creating HashMap
　　　　HashMap<String, Integer> languages = new HashMap<>();
　　　　//　Inserting items into HashMap
　　　　languages.put("Java",　14;
　　　　languages.put("Python",　3;
　　　　languages.put("JavaScript",　1;
　　　　//　Display HashMap
　　　　System.out.println("Programming languages: ")　+　languages);
　　　　}
}

Output Result

Programming languages: {Java=14, JavaScript=1, Python=3}

In the above example, we created a HashMap named languages. Here, the put() method willKey/Value mappingInsert into HashMap.

Note: Each item is inserted into the HashMap at a random position.

Example2: Inserting items with duplicate keys

import java.util.HashMap;
class Main {
　　public static void main(String[] args) {
　　　　//　Creating HashMap
　　　　HashMap<String, String> countries = new HashMap<>();
　　　　//Inserting items into HashMap
　　　　countries.put("Washington", "America");
　　　　countries.put("Ottawa", "Canada");
　　　　countries.put("Kathmandu", "Nepal");
　　　　System.out.println("Countries: ")　+　countries);
　　　　//Add elements with duplicate keys
　　　　String value = countries.put("Washington", "USA");
　　　　System.out.println("Updated Countries: ")　+　countries);
　　　　//　Display the replacement value
　　　　System.out.println("The replaced value: ");　+　value);
　　　　}
}

Output Result

Countries: {Kathmandu=Nepal, Ottawa=Canada, Washington=America}
Updated Countries: {Kathmandu=Nepal, Ottawa=Canada, Washington=USA}
The replaced value:

In the above example, we used the put() method to insert items into the hash table. Note this line,

countries.put("Washington", "USA");

In this case, the key 'Washington' already exists in the hash map. Therefore, the put() method replaces the previous value 'America' with the new value 'USA'.

NoteAs of now, we have only added one item. However, we can also useJava HashMap putAll()The method adds multiple items to the hash map.

Java HashMap Methods