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I have come across a strange behavior of Java that seems like a bug. Is it? Casting an Object to a generic type (say, K ) does not throw a ClassCastException even if the object is not an instance of K . Here is an example: import java.util.*; public final class Test { private static<K,V> void addToMap(Map<K,V> map, Object ... vals) { for(int i = 0; i < vals.length; i += 2) map.put((K)vals[i], (V)vals[i+1]); //Never throws ClassCastException! } public static void main(String[] args) { Map<String,Integer> m = new HashMap<String,Integer>(); addToMap(m, "hello", "world"); //No exception System.out.println(m.get("hello")); //Prints "world", which is NOT an Integer!! } } Update : Thanks to cletus and Andrzej Doyle for your helpful answers. Since I can only accept one, I'm accepting Andrzej Doyle's answer because it led me to a solution that I think isn't too bad. I think it's a little better way of initializing a small Map in a one-liner. /** * Creates a map with given keys/values. * * @param keysVals Must be a list of alternating key, value, key, value, etc. * @throws ClassCastException if provided keys/values are not the proper class. * @throws IllegalArgumentException if keysVals has odd length (more keys than values). */ public static<K,V> Map<K,V> build(Class<K> keyClass, Class<V> valClass, Object ... keysVals) { if(keysVals.length % 2 != 0) throw new IllegalArgumentException("Number of keys is greater than number of values."); Map<K,V> map = new HashMap<K,V>(); for(int i = 0; i < keysVals.length; i += 2) map.put(keyClass.cast(keysVals[i]), valClass.cast(keysVals[i+1]))

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