Java HashMap put() Method

Java HashMap

The put() method inserts the specified key/value pair into the HashMap.

The syntax for the put() method is:

hashmap.put(K key, V value)

Note: hashmap is an object of the HashMap class.

Parameter Description:

key - the key
value - the value

Return Value

If the key already exists, it replaces the existing value and returns the old value. If the key does not exist, it inserts the key/value pair and returns null.

Example

The following example demonstrates the use of the put() method when the key does not exist:

Example

import java.util.HashMap;

class Main {
    public static void main(String[] args) {
        // Create a HashMap
        HashMap&lt;Integer, String> sites = new HashMap<>();

        // Add some elements to the HashMap
        sites.put(1, "Google");
        sites.put(2, "tutorialpro");
        sites.put(3, "Taobao");
        System.out.println("HashMap: " + sites);
    }
}

Executing the above program outputs:

HashMap: {1=Google, 2=tutorialpro, 3=Taobao}

In the above example, we created a HashMap named sites and used the put() method to insert the key/value mappings into this HashMap.

To insert multiple key/value pairs, use the Java HashMap putAll() method.

Note: Each entry is inserted randomly into the HashMap.

Example of inserting when the key already exists:

Example

import java.util.HashMap;

class Main {
    public static void main(String[] args) {
        // Create a HashMap
        HashMap&lt;Integer, String> sites = new HashMap<>();

        // Add some elements to the HashMap
        sites.put(1, "Google");
        sites.put(2, "tutorialpro");
        sites.put(3, "Taobao");
        System.out.println("HashMap: " + sites);
        // Add a duplicate key element
        String value = sites.put(1, "Weibo");
        System.out.println("Modified HashMap: " + sites);

        // Check the replaced value
        System.out.println("Replaced value: " + value);
    }
}

Executing the above program outputs:

Modified HashMap: {1=Weibo, 2=tutorialpro, 3=Taobao}
Replaced value: Google

Java HashMap

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