Question

The following code

public class GenericsTest2 {      public static void main(String[] args) throws Exception {         Integer i = readObject(args[0]);         System.out.println(i);     }      public static <T> T readObject(String file) throws Exception {         return readObject(new ObjectInputStream(new FileInputStream(file)));         // closing the stream in finally removed to get a small example     }      @SuppressWarnings('unchecked')     public static <T> T readObject(ObjectInputStream stream) throws Exception {         return (T)stream.readObject();     } } 

compiles in eclipse, but not with javac (type parameters of T cannot be determined; no unique maximal instance exists for type variable T with upper bounds T,java.lang.Object).

When I change readObject(String file) to

    @SuppressWarnings('unchecked')     public static <T> T readObject(String file) throws Exception {         return (T)readObject(new ObjectInputStream(new FileInputStream(file)));     } 

it compiles in eclipse and with javac. Who is correct, the eclipse compiler or javac?

Answer 1

I’d say it’s the bug in the Sun compiler reported here and here, because if you change your line to the one below it works with both, which seems to be exactly what is described in the bug reports.

return GenericsTest2.<T>readObject(new ObjectInputStream(new FileInputStream(file)));