dogbane dogbane - 4 months ago 29
Java Question

How can I initialise a static Map?

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 two methods:

import java.util.HashMap;
import java.util.Map;

public class Test {
private static final Map<Integer, String> myMap = new HashMap<Integer, String>();
static {
myMap.put(1, "one");
myMap.put(2, "two");
}

private static final Map<Integer, String> myMap2 = new HashMap<Integer, String>(){
{
put(1, "one");
put(2, "two");
}
};
}

Answer

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);
    }
}
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