Difference between an unbound wildcard and a raw type

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How List<?> differs from List<Object>

The main difference is that the first line compiles but the second does not:

List<?> list = new ArrayList<String> ();
List<Object> list = new ArrayList<String> ();

However, because you don’t know what the generic type of List<?> is, you can’t use its parameterized methods:

List<?> list = new ArrayList<String> ();
list.add("aString"); //does not compile - we don't know it is a List<String>
list.clear(); //this is fine, does not depend on the generic parameter type

As for the difference with raw types (no generics), the code below compiles and runs fine:

List list = new ArrayList<String> ();
list.add("aString");
list.add(10);

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