Please read the comments in the code in order, the question details are there.
Why is this difference happening?
Please quote the JLS if possible.
import java.util.*;
/**
* Suppose I have a generic class
* @param <T> with a type argument.
*/
class Generic<T> {
// Apart from using T normally,
T paramMethod() { return null; }
// the class' interface also contains Generic Java Collections
// which are not using T, but unrelated types.
List<Integer> unrelatedMethod() { return null; }
}
@SuppressWarnings("unused")
public class Test {
// If I use the class properly (with qualified type arguments)
void properUsage() {
Generic<String> g = new Generic<String>();
// everything works fine.
String s = g.paramMethod();
List<Integer> pos = g.unrelatedMethod();
// OK error: incompatible types: List<String> := List<Integer>
List<String> thisShouldErrorCompile = g.unrelatedMethod();
}
// But when I use the raw type, *ALL* the generics support is gone, even the Collections'.
void rawUsage() {
// Using Generic<?> as the type turns fixes the warnings below.
Generic g = new Generic();
// OK error: incompatible types: String := Object
String s = g.paramMethod();
// WTF warning: unchecked conversion: List<Integer> := raw List
List<Integer> pos = g.unrelatedMethod();
// WTF warning: unchecked conversion: List<String> := raw List
List<String> thisShouldErrorCompile = g.unrelatedMethod();
}
}
Side note
I originally found this in IntelliJ IDEA, but I guess that compiler is compatible with javac because when I compiled the above code with the following it gave the same errors/warnings.
$ javac -version
javac 1.7.0_05
$ javac Test.java -Xlint:unchecked
...
$ javac Test.java -Xlint:unchecked -source 1.5 -target 1.5
...
