How to do this in Java - passing a collection of subtype to a method requiring a collection of base type?
The example below gives:
The method foo(Map<String,List>) is not applicable for the arguments (Map<String,MyList>)
I can implement by creating a class hierarchy for the typed collections - but is it possible otherwise?
public void testStackOverflow() {
class MyList extends AbstractList {
public Object get(int index) {
return null;
}
public int size() {
return 0;
}
};
Map <String, List> baseColl = null;
Map <String, MyList> subColl = null;
foo (subColl);
}
private void foo (Map <String, List> in) {
}
EDIT: Turns out from the answers that this requires "bounded wildcard" so adding this text for searchability
Change foo
to:
private void foo(Map <String, ? extends List> in) {
}
That will restrict what you can do within foo
, but that's reasonable. You know that any value you fetch from the map will be a list, but you don't know what kind of value is valid to put into the map.
as jon s says:
private void foo (Map <String, ? extends List> in { ... }
will fix the errors. you will still have warnings though. take a look the get-put principle at: http://www.ibm.com/developerworks/java/library/j-jtp07018.html
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