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How would you initialise a static Map in Java?
Method one: static initialiser
Method two: instance initialiser (anonymous subclass) or some other method?
What are the pros and cons of each?
Here is an example illustrating the two methods:
import java.util.HashMap; import java.util.Map; public class Test { private static final Map<Integer, String> myMap = new HashMap<>(); static { myMap.put(1, "one"); myMap.put(2, "two"); } private static final Map<Integer, String> myMap2 = new HashMap<>(){ { put(1, "one"); put(2, "two"); } }; } 
824
We use a simple utility class to initialize Maps in a fluent way: Map<String, String> map = MapInit . init("key1", "value1") . put("key2", "value2") .
In this article, a static map is created and initialized 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.
std::cout << registers["Plop"] << std::endl; // prints 0. This works because even though registers is empty. The operator [] will insert the key into the map and define its value as the default for the type (in this case integers are zero).
The instance initialiser is just syntactic sugar in this case, right? I don't see why you need an extra anonymous class just to initialize. And it won't work if the class being created is final.
You can create an immutable map using a static initialiser too:
public class Test { private static final Map<Integer, String> myMap; static { Map<Integer, String> aMap = ....; aMap.put(1, "one"); aMap.put(2, "two"); myMap = Collections.unmodifiableMap(aMap); } } 
answered Sep 21 '22 22:09
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