How to Add a Key-Value Pair to a Map in Java - Step by Step Examples

How to Add a Key-Value Pair to a Map in Java ?

Answer

To add a key-value pair to a map in Java, you can use the put method.

✐ Examples

1 Adding a Key-Value Pair Using put Method

We can add a key-value pair to 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 add a new key-value pair to the map. The put method takes two arguments: the key and the value to be added.
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");

        // Add a key-value pair using put method
        myMap.put(4, "four");

        // 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
4: four

2 Adding Multiple Key-Value Pairs Using put Method

We can add multiple key-value pairs to a map in Java using the put method.

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 add multiple new key-value pairs to the map. The put method takes two arguments: the key and the value to be added.
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");

        // Add multiple key-value pairs using put method
        myMap.put(4, "four");
        myMap.put(5, "five");

        // 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
4: four
5: five

3 Adding a Key-Value Pair Using putIfAbsent Method

We can add a key-value pair to a map in Java using the putIfAbsent method, which associates the specified value with the specified key in the map if the key is not already present.

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 putIfAbsent method to add a new key-value pair to the map if the key is not already present. The putIfAbsent method takes two arguments: the key and the value to be added.
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");

        // Add a key-value pair using putIfAbsent method
        myMap.putIfAbsent(4, "four");

        // 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
4: four

Summary

In this tutorial, we learned How to Add a Key-Value Pair to a Map in Java language with well detailed examples.

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How to Add a Key-Value Pair to a Map in Java - Step by Step Examples