Bug in eclipse compiler or in javac ("type parameters of T cannot be determined")
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?
我想说这是Sun编译器在这里和这里报告的错误，因为如果您将行更改为下面的行，它就可以与两者一起使用，这似乎正是bug报告中所描述的。
return GenericsTest2.<T>readObject(new ObjectInputStream(new FileInputStream(file)));
In this case, I'd say your code is wrong (and the Sun compiler is right). There is nothing in your input arguments to readObject to actually infer the type T . In that case, you're better off to let it return Object, and let clients manually cast the result type.
This should work (though I haven't tested it):
public static <T> T readObject(String file) throws Exception {
return GenericsTest2.<T>readObject(new ObjectInputStream(new FileInputStream(file)));
}
Oracle JDK6 u22 should be correct but I've this problem with JDK6 u24 too
This is a bug of eclipse bug 98379.
This was not corrected but the problem is resolved via workaround like example in eclipse bugs (see link)
链接地址: http://www.djcxy.com/p/79952.html