Java Generics non-issue at compile time

Question

The code below compiles without errors ... at one time I would prefer it to fail: /

Map <Character, Double> m = new HashMap <Character, Double>(); m.get(new String()); 

Since the compiler knows that the key used on this card is of type Character, the String character should be used instead.

What am I missing?

Answer 1

You have not missed anything. All Map#get() calls simply accept an Object .

Depending on your implementation, you may see a (runtime) ClassCastException when you pass a String to Map<Character, Double>#get() .

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This is why Map#get() not completely general .

Answer 2

If you try to run this code, you will not have a (optional) runtime exception ( ClassCastException ).

Answer 3

That the get method is not parameterized with a common parameter is the result.

You can also do

 m.get(1L); //m.get(Object o); 

Parameterized method is placed

 m.put(new String(), 0.0); //Fail //The method put(Character, Double) in the type Map<Character,Double> is not applicable for the arguments (String, double) m.put(new Character('c'), 0.0); //Ok 

Answer 4

Map.get () takes an object as an argument: java.util.Map # will arrive

Answer 5

get retrieves the object for which the argument .equals() to. This is possible for an .equals() object for an object of another class.