java - Compilation (genericity) issues overriding Properties.putAll -

for javafx ui, implemented class observableproperties extends java.util.properties , enables listen changes of properties (in particular, localized texts of ui).

it works fine override putall method , having issues that.

first, properties extends hashtable<object,object>, expect able override

@override public void putall(map<object,object> that) 

but compile won't let me (saying i'm not overriding super method), have use

@override public void putall(map that) 

i want perform action on entries of that tried usual

for (map.entry entry : that.entryset()) 

but compiler tells me type mismatch: cannot convert element type object map.entry. however, second snippet

set<map.entry> set = that.entryset(); (map.entry : set); 

it compiles...

to sum up, know :

• why have remove bounds of map<k,v> in signature
• why first for loop not compile whereas seems equivalent second one

thanks in advance !

you have signature of putall method wrong. override method hasttable signature must match, should be:

@override public synchronized void putall(map<? extends object, ? extends object> t) { } 

the ? extends object allows pass typed map method. if signature putall(map<object,object> t) able pass maps of type map<object,object>. passing map<string,string> example give error.

the first loop won't compile because that.entryset() returning set of type set<object>. loop won't convert object map.entry you.

the second loop works, type safety warnings, because you're telling compiler set of type set<map.entry> before pass loop.