JIYIK CN >

This article explains how to use the two methods contained in the HashMap class in Java - update put()and replace()update the values ​​in a HashMap.

hashmap.put()Update the value in Hashmap in Java using

When we want to HashMapinsert a value in , we use put()the method. We can also use it to update HashMapthe value in . In the following example, we create an HashMapobject of , which is composed of key-value pairs. When initializing, we need to define the data types of keys and values.

We use string types for both keys and values, and we can use the key to find or operate on the value. Below, we replace threethe value with key with a new value. If the HashMapvalue we want to update does not exist in , using put()the method, a new value will be inserted. The output shows the updated value.

import java.util.HashMap;

public class UpdateHashmap {
  public static void main(String[] args) {
    HashMap<String, String> ourHashmap = new HashMap<>();

    ourHashmap.put("one", "Alex");
    ourHashmap.put("two", "Nik");
    ourHashmap.put("three", "Morse");
    ourHashmap.put("four", "Luke");

    System.out.println("Old Hashmap: " + ourHashmap);
    ourHashmap.put("three", "Jake");

    System.out.println("New Hashmap: " + ourHashmap);
  }
}

Output:

Old Hashmap: {four=Luke, one=Alex, two=Nik, three=Morse}
New Hashmap: {four=Luke, one=Alex, two=Nik, three=Jake}

hashmap.replace()Update the value in Hashmap in Java using

HashMapAnother method of the class is replace()that it can update or replace HashMapexisting values ​​in . The biggest difference put()between and is that when a key does not exist in , the method will insert the key and value into , but the method will return null. This makes it safer to use when updating values ​​in .replace()HashMapput()HashMapreplace()replace()HashMapreplace()

In the following example, we create a HashMapand insert some key-value pairs. Then to update threethe value attached to the key , we use ourHashMap.replace(key, value), which takes two parameters, the first is the key we want to update and the second is the value.

import java.util.HashMap;

public class UpdateHashmap {
  public static void main(String[] args) {
    HashMap<String, String> ourHashmap = new HashMap<>();

    ourHashmap.put("one", "Alex");
    ourHashmap.put("two", "Nik");
    ourHashmap.put("three", "Morse");
    ourHashmap.put("four", "Luke");

    System.out.println("Old Hashmap: " + ourHashmap);
    ourHashmap.replace("three", "Jake");

    System.out.println("New Hashmap: " + ourHashmap);
  }
}

Output:

Old Hashmap: {four=Luke, one=Alex, two=Nik, three=Morse}
New Hashmap: {four=Luke, one=Alex, two=Nik, three=Jake}