Description Brad Cupit 2006-07-20 12:48:50 EDT

When the only way to infer the type of a Type Parameter is based on the type of the return value, and if the return value is expected to be a primitive type, Eclipse knows to use the wrapper type, but javac fails.

Example code:

class GenericTest {
    public static void main(String[] args) {
        Integer castInteger = genericCast(1);               // works
        int castInt1 = genericCast(1);                      // fails in javac but works in Eclipse
        int castInt2 = GenericTest.<Integer>genericCast(1); // workaround for javac
        int castInt3 = (Integer) genericCast(1);            // workaround for javac
    }
    
    private static <T> T genericCast(Object input) {
        @SuppressWarnings("unchecked")
        T castValue = (T) input;
        
        return castValue;
    }
}

I'm not sure which side the bug is in (Eclipse or javac) but I like the Eclipse functionality much better. Unfortunately the discrepancy between the two compilers has caused issues in our build process.

The workaround for javac is to cast the value to the wrapper type, or to explicitly state the Generic type when invoking the method.

javac generates the following error:
type parameters of <T>T cannot be determined; no unique maximal instance exists for type variable T with upper bounds int,java.lang.Object

The following bugs might be related to this (although they each seem very different to me):
Bug 81923
Bug 101779
Bug 105524