In Java, double brace initialization is a combination of two separate processes. The two consecutive curly braces {{ involved in it.
The first curly brace represents the creation of an anonymous inner class. Remember that the second curly brace will not be considered in such a case. It is just like creating an anonymous inner class.
The second curly brace represents an initialization block that we have seen in it as a class for initialization. When we use the initialization block for an anonymous inner class it becomes Java double brace initialization. The inner class has a reference to the enclosing outer class. We can use the reference by using this pointer.
It is used to initialize collections because it is easier to initialize a constant collection using double brace initialization. The example of double brace initialization is as follows :
import java.util.*;
public class Demo
{
public static void main(String args[])
{
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-------------------
Map<String, Map<String, Integer>> map = new HashMap <String, Map<String, Integer>> {{
put ("VEGETABLES", new HashMap<String, Integer>() {{
put("Tomato", 300);
put("Onion", 50);
put("Carrot", 100);
put("Beetroot", 40);
}}
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-------------------
);
}};
System.out.println(map);
}
}​
