Increment Map in Java

MD Aminul Islam Oct 12, 2023 Java Java Map
  1. Method 1: General Method for Incrementing Map Value in Java
  2. Method 2: Increment Map Value Using containsKey() in Java
  3. Method 3: Increment Map Value Using AtomicInteger or MutableInt Class in Java
Increment Map in Java

You may need to increment the value when working with Maps or HashMaps in Java. In Java, there are many ways to increment the Map’s value.

In this article, we will see how we can increment a Map value in Java, along with some necessary examples and explanations to make the topic easier.

Before we go to the example, let’s look at the basic steps required to increment a Map value.

  1. To increment the value, firstly, we need to get the key of the Map.
  2. After that, we need to get the current value from the Map.
  3. We can easily increase the Map value by using any of the methods shared below.

Let’s see the example from this method.

Method 1: General Method for Incrementing Map Value in Java

Our example below illustrates the simplest method of incrementing the Map. Take a look at the example code.

// Importing necessary packages
import java.util.HashMap;
import java.util.Map;

// Our main class
class Main {
  public static <K> void IncrementMapValue(Map<K, Integer> MyMap, K key) {
    // Collecting the Map key
    Integer count = MyMap.get(key);

    // Checking whether the Map value is null
    if (count == null) {
      count = 0;
    }

    // increment the Map value
    MyMap.put(key, count + 1);
  }

  public static void main(String[] args) {
    Map<String, Integer> MyMap = new HashMap(); // Creating an object of Map
    MyMap.put("Value-A", 100); // Putting a value for MyMap

    IncrementMapValue(MyMap, "Value-A"); // Incrementing value
    IncrementMapValue(MyMap, "Value-B"); // Incrementing value

    System.out.println(MyMap);
  }
}

We already commented on each line’s purpose, and after executing the above example code, you will get an output like the one below.

{Value-B=1, Value-A=101}

Method 2: Increment Map Value Using containsKey() in Java

// Importing necessary packages
import java.util.HashMap;
import java.util.Map;

// Our main class
class Main {
  public static <K> void IncrementMapValue(Map<K, Integer> MyMap, K key) {
    // Collecting the Map key and getting the current value of the Map
    Integer count = MyMap.containsKey(key) ? MyMap.get(key) : 0;
    MyMap.put(key, count + 1); // increment the Map value
  }

  public static void main(String[] args) {
    Map<String, Integer> MyMap = new HashMap(); // Creating an object of Map
    MyMap.put("Value-A", 100); // Putting a value for MyMap

    IncrementMapValue(MyMap, "Value-A"); // Incrementing value
    IncrementMapValue(MyMap, "Value-B"); // Incrementing value

    System.out.println(MyMap);
  }
}

We already commented on the purpose of each line. In the example above, the containsKey() checks whether the Map contains any mapping for the key.

After executing the above example code, you will get an output like the one below.

{Value-B=1, Value-A=101}

Method 3: Increment Map Value Using AtomicInteger or MutableInt Class in Java

// Importing necessary packages
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicInteger;

// Our main class
class Main {
  public static <K> void IncrementMapValue(Map<K, Integer> MyMap, K key) {
    // Collecting the Map key and getting the current value of the Map
    AtomicInteger AtomicInt = new AtomicInteger(MyMap.containsKey(key) ? MyMap.get(key) : 0);
    MyMap.put(key, AtomicInt.incrementAndGet()); // increment the Map value
  }

  public static void main(String[] args) {
    Map<String, Integer> MyMap = new HashMap(); // Creating an object of Map
    MyMap.put("Value-A", 100); // Putting a value for MyMap

    IncrementMapValue(MyMap, "Value-A"); // Incrementing value
    IncrementMapValue(MyMap, "Value-B"); // Incrementing value

    System.out.println(MyMap);
  }
}