Question

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');         }     }; } 

Answer 1

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);     } }