The syntax of the put()
method is:
hashmap.put(K key, V value)
Here, hashmap is an object of the HashMap
class.
put() Parameters
The put()
method takes two parameters:
- key - the specified value is mapped with this key
- value - the specified key is mapped with this value
put() Return Value
- if key is already associated with any value, returns the previously associated value
- if key is not associated with any value, returns
null
Note: If key is previously associated with a null value, then also the method returns null
.
Example 1: Java HashMap put()
import java.util.HashMap;
class Main {
public static void main(String[] args) {
// create an HashMap
HashMap<String, Integer> languages = new HashMap<>();
// insert items to the HashMap
languages.put("Java", 14);
languages.put("Python", 3);
languages.put("JavaScript", 1);
// display the HashMap
System.out.println("Programming Languages: " + languages);
}
}
Output
Programming Languages: {Java=14, JavaScript=1, Python=3}
In the above example, we have created a HashMap
named languages. Here, the put()
method inserts the key/value mappings to the hashmap.
Note: Every item is inserted in random positions in the HashMap
.
Example 2: Insert Item with Duplicate Key
import java.util.HashMap;
class Main {
public static void main(String[] args) {
// create an HashMap
HashMap<String, String> countries = new HashMap<>();
// insert items to the HashMap
countries.put("Washington", "America");
countries.put("Ottawa", "Canada");
countries.put("Kathmandu", "Nepal");
System.out.println("Countries: " + countries);
// add element with duplicate key
String value = countries.put("Washington", "USA");
System.out.println("Updated Countries: " + countries);
// display the replaced value
System.out.println("Replaced Value: " + value);
}
}
Output
Countries: {Kathmandu=Nepal, Ottawa=Canada, Washington=America} Updated Countries: {Kathmandu=Nepal, Ottawa=Canada, Washington=USA} Replaced Value: America
In the above example, we have used the put()
method to insert items to the hashmap. Notice the line,
countries.put("Washington", "USA");
Here, the key Washington is already present in the hashmap. Hence, the put() method replaces the previous value America with the new value USA.
Note: Till now, we have only added a single item. However, we can also add multiple items from Map
to a hashmap using the Java HashMap putAll() method.