Initialization of a Static Map: null value returned

Question

Following the answers of this question: How can I initialise a static Map? I'm trying to create a static Map in my project.
Below a code snippet:

public class MyClass {

    public static final Map<String, String> dataMap;

    static {
        Map<String, String> tempMap = new HashMap<String, String>();
        try {
           // Getting a string value from a file, e.g. String data
           String data = "data";
           tempMap.put("firstData", data);
        }
        catch(Exception e) {}

        dataMap = Collections.unmodifiableMap(tempMap);

        //DEBUG (I test it and it correctly prints "data")
        System.out.println(dataMap.get("firstData"));
     }
}

Then I call the map in another class, like this:

public class AnotherClass {

   @Before
   public void MyMethod() {
      System.out.println(MyClass.dataMap.get("firstData"));
   }

   @Test
   public void testMethod() {}
}

Now it prints null, instead of the value "data".
Why?

No, it doesn't. But that is not your real code, because it doesn't even compile. — JB Nizet, Apr 01 '17 at 15:32
Because there is a missing semicolon in MyMethod. Post a complete minimal example reproducing the problem. If I take this code and fix it, and add a main method calling MyMethod, I can't reproduce the error (as I expected). — JB Nizet, Apr 01 '17 at 15:41
Can't reproduce. You probably have another class named MyClass, or forgot to recompile, or something like that. — JB Nizet, Apr 01 '17 at 15:49

score 0 · Answer 1 · answered Apr 01 '17 at 15:37

0

Are you sure your map is not modified somewhere else (cleared, ...) ? Because this code should work.

I don't think that "unmodifiableMap" is usefull when you are using "final", it just protects that the map will not be modified by reference. So values can change by an external call.

answered Apr 01 '17 at 15:37

cactuschibre

1,908
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The only difference seems to be that the method MyMethod is annotated with @Before annotation, because it is a test – PenguinEngineer Apr 01 '17 at 15:38
3

unmodifiableMap() is very important. Otherwise, you can just get a reference to that map and clear it (or adding/removing elements) from anywhere, although that is probably not desired. – JB Nizet Apr 01 '17 at 15:39
@PenguinEngineer post a complete minimal example reproducing the problem. – JB Nizet Apr 01 '17 at 15:40

Ron Badur · Answer 2 · 2017-04-01T16:08:09.640

0

When I executing the same code on my machine it's work and print data twice as you excpected , This code is not your problem.

UPDATE: maybe MyClass refer to another MyClass in your package? check your imports.. try to compile in and run it from the command line and check if you get the same results , there is something you missing here

edited Apr 01 '17 at 16:08

answered Apr 01 '17 at 15:49

Ron Badur

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Initialization of a Static Map: null value returned

2 Answers2