Putting stuff in Map<?,?> or converting Map<String,String> to Map<?,?>

Question

I'm unhappily dealing with an interface someone defined with the following

public Map<?, ?> getMap(String key);

I'm trying to write unit tests that consume this interface.

Map<String,String> pageMaps = new HashMap<String,String();
pageMaps.put(EmptyResultsHandler.PAGEIDENT,"boogie");
pageMaps.put(EmptyResultsHandler.BROWSEPARENTNODEID, "Chompie");
Map<?,?> stupid = (Map<?, ?>)pageMaps;
EasyMock.expect(config.getMap("sillyMap")).andReturn(stupid);

and the compiler is borking.

The method andReturn(Map<capture#5-of ?,capture#6-of ?>) in the type IExpectationSetters<Map<capture#5-of ?,capture#6-of ?>> is not applicable for the arguments (Map<capture#7-of ?,capture#8-of ?>)

If I try to use pageMaps directly, it tells me:

The method andReturn(Map<capture#5-of ?,capture#6-of ?>) in the type IExpectationSetters<Map<capture#5-of ?,capture#6-of ?>> is not applicable for the arguments (Map<String,String>)

If I make pageMaps a Map<?,?>, I can't put Strings inside of it.

The method put(capture#3-of ?, capture#4-of ?) in the type Map<capture#3-of ?,capture#4-of ?> is not applicable for the arguments (String, String)

I've seen some client code that does ugly unchecked conversions, like

@SuppressWarnings("unchecked")
        final Map<String, String> emptySearchResultsPageMaps = (Map<String, String>) conf.getMap("emptySearchResultsPage");

How do I get data into a Map<?,?>, or convert my Map<String,String> to Map<?,?> ?

There is kind of confusion here: You try to convince the compiler that stupid is a Map with 2 type arguments you don't care about, but nevertheless, you use the Map at the type Map<String, String>. But what you should do is to test that the interface works for any combination of types you need. — Ingo
– Ingo, Commented Feb 24, 2013 at 10:17
What happens if you make it return pageMaps? EasyMock.expect(config.getMap("sillyMap")).andReturn(pageMaps); — JB Nizet
– JB Nizet, Commented Feb 24, 2013 at 10:20
I only care about it as a Map<String,String> for this test, but that is irrelevant. I don't see how I can "test that the interface works for any combination of types that I need" if I cannot get data into it. If I make the map completely generic, put() refuses to work. — Visionary Software Solutions
– Visionary Software Solutions, Commented Feb 24, 2013 at 10:23
@JBNizet That was what I meant by "when I true to use pageMaps directly" — Visionary Software Solutions
– Visionary Software Solutions, Commented Feb 24, 2013 at 10:24

assylias · Accepted Answer · 2013-02-24 10:28:06Z

5

There is no way you can write Map<String, String> map = getMap("abc"); without a cast

The problem has more to do with easymock and the types returned/expected by the expect and andReturn methods, which I'm not familiar with. You could write

Map<String, String> expected = new HashMap<String, String> ();
Map<?, ?> actual = getMap("someKey");
boolean ok = actual.equals(pageMaps);
//or in a junit like syntax
assertEquals(expected, actual);

Not sure if that can be mixed with your mocking stuff. This would maybe work:

EasyMock.expect((Map<String, String>) config.getMap("sillyMap")).andReturn(pageMaps);

Also note that you can't add anything to a generic collection with a wildcard. So this:

Map<?, ?> map = ...
map.put(a, b);

won't compile, unless a and b are null.

edited Feb 24, 2013 at 10:28

answered Feb 24, 2013 at 10:21

assylias

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1 Comment

Visionary Software Solutions Over a year ago

Nicely done, I hadn't thought of trying to cast inside of the expect call.

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