How to Get the Size (Number of Key-Value Pairs) of a Map in Java - Step by Step Examples

How to Get the Size (Number of Key-Value Pairs) of a Map in Java ?

Answer

To get the size (number of key-value pairs) of a map in Java, you can use the size() method. This method returns the number of elements in the map.

✐ Examples

1 Getting the Size of a Map Using size() Method

We can get the size of a map in Java using the size() method, which provides the number of key-value pairs 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 size method to get the number of key-value pairs in the map.
We store the size in a variable named mapSize.
We print the size to the console using the System.out.println function to verify the number of key-value pairs in the map.

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");

        // Get the size of the map
        int mapSize = myMap.size();

        // Print the size
        System.out.println("Size of the map: " + mapSize);
    }
}

Output

Size of the map: 3

2 Getting the Size of an Empty Map

We can also get the size of an empty map in Java using the size() method, which returns 0 when the map is empty.

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 an empty map named emptyMap with integer keys and string values.
We use the size method to get the number of key-value pairs in the empty map.
We store the size in a variable named emptyMapSize.
We print the size to the console using the System.out.println function to verify that the map is empty.

Java Program

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

public class Main {
    public static void main(String[] args) {
        // Declare an empty map
        Map<Integer, String> emptyMap = new HashMap<>();

        // Get the size of the empty map
        int emptyMapSize = emptyMap.size();

        // Print the size
        System.out.println("Size of the empty map: " + emptyMapSize);
    }
}

Output

Size of the empty map: 0

3 Getting the Size of a Map After Adding Elements

We can get the size of a map in Java after adding elements using the size() method, which provides the updated number of key-value pairs 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 an empty map named dynamicMap with integer keys and string values.
We add some key-value pairs to the map using the map's put method.
We use the size method to get the number of key-value pairs in the map after adding elements.
We store the size in a variable named dynamicMapSize.
We print the size to the console using the System.out.println function to verify the updated number of key-value pairs in the map.

Java Program

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

public class Main {
    public static void main(String[] args) {
        // Declare an empty map
        Map<Integer, String> dynamicMap = new HashMap<>();

        // Add elements to the map
        dynamicMap.put(1, "one");
        dynamicMap.put(2, "two");
        dynamicMap.put(3, "three");

        // Get the size of the map after adding elements
        int dynamicMapSize = dynamicMap.size();

        // Print the size
        System.out.println("Size of the map after adding elements: " + dynamicMapSize);
    }
}

Output

Size of the map after adding elements: 3

Summary

In this tutorial, we learned How to Get the Size (Number of Key-Value Pairs) of a Map in Java language with well detailed examples.

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How to Get the Size (Number of Key-Value Pairs) of a Map in Java - Step by Step Examples