How to Merge Two Maps in Java - Step by Step Examples

How to Merge Two Maps in Java ?

Answer

To merge two maps in Java, you can use the putAll() method to add key-value pairs from one map to another. This method provides a straightforward way to combine the contents of two maps.

✐ Examples

1 Merging Two Maps Using putAll() Method

We can merge two maps in Java using the putAll() method, which adds all key-value pairs from one map to another.

For example,

We start by importing the java.util.HashMap package, which provides the HashMap class needed to create and manipulate the maps.
We declare and initialize two maps named map1 and map2 with some key-value pairs. In this example, both maps have integer keys and string values.
We use the putAll() method to add all key-value pairs from map2 to map1.
We print the merged map to the console using the System.out.println function to verify the merge.

Java Program

import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        // Declare and initialize two maps
        HashMap<Integer, String> map1 = new HashMap<>();
        map1.put(1, "one");
        map1.put(2, "two");

        HashMap<Integer, String> map2 = new HashMap<>();
        map2.put(3, "three");
        map2.put(4, "four");

        // Merge map2 into map1
        map1.putAll(map2);

        // Print the merged map
        System.out.println("Merged Map: " + map1);
    }
}

Output

Merged Map: {1=one, 2=two, 3=three, 4=four}

2 Merging Two Maps with Overlapping Keys Using putAll() Method

We can merge two maps in Java and handle overlapping keys by using the putAll() method, which updates the values for overlapping keys.

For example,

We start by importing the java.util.HashMap package, which provides the HashMap class needed to create and manipulate the maps.
We declare and initialize two maps named map1 and map2 with some key-value pairs. In this example, both maps have integer keys and string values, and there is an overlapping key.
We use the putAll() method to add all key-value pairs from map2 to map1.
We print the merged map to the console using the System.out.println function to verify the merge.

Java Program

import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        // Declare and initialize two maps with overlapping keys
        HashMap<Integer, String> map1 = new HashMap<>();
        map1.put(1, "one");
        map1.put(2, "two");

        HashMap<Integer, String> map2 = new HashMap<>();
        map2.put(2, "TWO");
        map2.put(3, "three");

        // Merge map2 into map1, updating values for overlapping keys
        map1.putAll(map2);

        // Print the merged map
        System.out.println("Merged Map: " + map1);
    }
}

Output

Merged Map: {1=one, 2=TWO, 3=three}

Summary

In this tutorial, we learned How to Merge Two Maps in Java language with well detailed examples.

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How to Merge Two Maps in Java - Step by Step Examples