Initialize a static Map in Java using Double Brace Initialization

Last Updated : 03 Dec, 2019

In this article, a static map is created and initialised in Java using Double Brace Initialization.

Static Map in Java
A static map is a map which is defined as static. It means that the map becomes a class member and can be easily used using class.

Double Brace Initialization
In Double Brace Initialization:

The first brace creates a new Anonymous Inner Class. These inner classes are capable of accessing the behaviour of their parent class. So, in our case, we are actually creating a subclass of HashMap class, so this inner class is capable of using put() method.
The second braces are instance initializers. The code an instance initializers inside is executed whenever an instance is created.

Approach:

Pass the map values as Key and Value pair in the Double braces.
A static factory Map instance is returned.
Store it in Map and use.

Below is the implementation of the above approach:

Example 1:

// Java program to create a static map
// using Double Brace Initialization
  
import java.util.*;
  
class GFG {
  
    // Declaring and instantiating the static map
    // using Double Brace Initialization
    private static Map<String, String> map
        = new HashMap<String, String>() {{
            put("1", "GFG");
            put("2", "Geek");
            put("3", "GeeksForGeeks");
        }};
  
    // Driver code
    public static void main(String[] args)
    {
        System.out.println(map);
    }
}

Output:

{1=GFG, 2=Geek, 3=GeeksForGeeks}

Example 2: To show with 10 key-value pairs

// Java program to create a static map
// using Double Brace Initialization
  
import java.util.*;
  
class GFG {
  
    // Declaring and instantiating the static map
    // using Double Brace Initialization
    private static Map<String, String> map
        = new HashMap<String, String>() {{
            put("1", "GFG");
            put("2", "Geek");
            put("3", "GeeksForGeeks");
            put("4", "G");
            put("5", "e");
            put("6", "e");
            put("7", "k");
            put("8", "s");
            put("9", "f");
            put("10", "o");
        }};
  
    // Driver code
    public static void main(String[] args)
    {
        System.out.println(map);
    }
}

Output:

{1=GFG, 2=Geek, 3=GeeksForGeeks, 4=G, 5=e, 6=e, 7=k, 8=s, 9=f, 10=o}

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