Use of generics in the Map interface

Question

After using Java 1.5 for a while, I've gotten pretty comfortable using generics and the collections framework. Very often, I depend on the new generics-related compiler warnings to guide me when I've made changes to my code. Recently, I missed a fairly subtle bug because of the following issue. Why isn't the get() method in the java.util.Map interface declared as:
V get(K key);Is there some subtle reason why this method isn't declared to enforce the generic type K for the key value? Likewise for containsKey() and remove() as well.
Thanks!

Answer 1

So where is the problem to use K in the first
place??The cast to K is removed during complilation. It's
not going to do anything at runtime.
Just because a reference is of type Object doesn't
mean it's not a K.
If I get an Object of unknown type, why should I have
to down-cast it just so that I can check to see
whether it is in the Map?
To state the point I wrote this simple code:
        Map<String,Integer> testMap = new TreeMap<String,Integer>();
        testMap.put("test", Integer.valueOf(100));
        // test the get method
        Integer value = testMap.get("test");
        System.out.println("First value: " + value);
        // test the method with differing parameter
        value = testMap.get(Float.valueOf(2));
        System.out.println("Second value: " + value);The code compiles without any error (so far so good) but the execution of this code results in Exception in thread "main" java.lang.ClassCastException: java.lang.String
     at java.lang.Float.compareTo(Unknown Source)
     at java.util.TreeMap.compare(Unknown Source)
     at java.util.TreeMap.getEntry(Unknown Source)
     at java.util.TreeMap.get(Unknown Source)
     at MapTest.main(MapTest.java:27)So when the Object parameter is allowed (I'm okay with that) why the ClassCastException. A similar approach to the implementations of Lists would be necessary. The current implementation is not satisfactory.