Java .put()

In Java, the .put() method adds a key-value pair to a HashMap; if the key already exists, it updates the corresponding value.

Syntax

hashMap.put(key, value);

Parameters:

• key: The key with which the given value is to be associated.
• value: The value to be associated with the specified key.

Return value:

Returns the previous value associated with the specified key, or null if the key was not previously present in the map.

Example

This example demonstrates how to use the .put() method to add and update key-value pairs in a HashMap:

import java.util.HashMap;

public class HashMapExample {
  public static void main(String[] args){
    HashMap<String, Integer> ages = new HashMap<String, Integer>();

    // Adding key-value pairs to the HashMap
    ages.put("Alice", 25);
    ages.put("Bob", 27);
    ages.put("Charlie", 30);

    // Printing the HashMap
    System.out.println("HashMap: " + ages);

    // Updating the value for an existing key
    Integer previousAge = ages.put("Alice", 26);
    System.out.println("Previous age of Alice: " + previousAge);
    System.out.println("Updated HashMap: " + ages);
  }
}

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The output of this code is:

HashMap: {Bob=27, Alice=25, Charlie=30}
Previous age of Alice: 25
Updated HashMap: {Bob=27, Alice=26, Charlie=30}

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