How to Update the Value for a Key in a Map in Java - Step by Step Examples

How to Update the Value for a Key in a Map in Java ?

Answer

To update the value for a key in a map in Java, you can use the put method or the replace method. These methods allow you to modify the value associated with a specific key directly.

✐ Examples

1 Updating the Value Using put Method

We can update the value for a key in a map in Java using the put method, which associates the specified value with the specified key in the map.

For example,

We start by importing the java.util.HashMap package, which provides the HashMap class needed to create and manipulate the map.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the put method to update the value for a specific key in the map. The put method takes the key and the new value to be assigned.
We print the updated map to the console using a for-each loop and System.out.println.

Java Program

import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        // Declare and initialize a map
        Map<Integer, String> myMap = new HashMap<>();
        myMap.put(1, "one");
        myMap.put(2, "two");
        myMap.put(3, "three");

        // Update the value using put method
        myMap.put(2, "TWO");

        // Print the updated map
        for (Map.Entry<Integer, String> entry : myMap.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

Output

1: one
2: TWO
3: three

2 Updating the Value Using replace Method

We can update the value for a key in a map in Java using the replace method, which replaces the value for a specified key only if it is already mapped.

For example,

We start by importing the java.util.HashMap package, which provides the HashMap class needed to create and manipulate the map.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the replace method to update the value for a specific key in the map. The replace method takes the key and the new value to be assigned.
We print the updated map to the console using a for-each loop and System.out.println.

Java Program

import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        // Declare and initialize a map
        Map<Integer, String> myMap = new HashMap<>();
        myMap.put(1, "one");
        myMap.put(2, "two");
        myMap.put(3, "three");

        // Update the value using replace method
        myMap.replace(2, "TWO");

        // Print the updated map
        for (Map.Entry<Integer, String> entry : myMap.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

Output

1: one
2: TWO
3: three

3 Updating the Value Conditionally Using computeIfPresent Method

We can update the value for a key in a map in Java using the computeIfPresent method, which updates the value for a specified key only if it is already mapped.

For example,

We start by importing the java.util.HashMap package, which provides the HashMap class needed to create and manipulate the map.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the computeIfPresent method to update the value for a specific key in the map. The computeIfPresent method takes the key and a function that computes the new value to be assigned.
We print the updated map to the console using a for-each loop and System.out.println.

Java Program

import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        // Declare and initialize a map
        Map<Integer, String> myMap = new HashMap<>();
        myMap.put(1, "one");
        myMap.put(2, "two");
        myMap.put(3, "three");

        // Update the value conditionally using computeIfPresent method
        myMap.computeIfPresent(2, (key, value) -> "TWO");

        // Print the updated map
        for (Map.Entry<Integer, String> entry : myMap.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

Output

1: one
2: TWO
3: three

Summary

In this tutorial, we learned How to Update the Value for a Key in a Map in Java language with well detailed examples.

◀ Previous Next ▶

Java Tutorials

Java How-Tos

How to Update the Value for a Key in a Map in Java - Step by Step Examples