receiving other reference type in Java

Question

There is a parameter which is reference type, and can it receive other reference type? for instance, there is a code below

fr = new FileReader("d:\\test.txt");
br = new BufferedReader(fr);

the BufferedReader class receives FileReader type but I see in the JAVA API

BufferedReader(Reader in)

receives Reader type.

I know Reader class is abstract but it doesn't give me a clue. How is getting other types of reference as a parameter possible?

Answer 1

FileReader is a subclass of InputStreamReader, which is a subclass of Reader. That said, all public methods and variables from Reader are available in FileReader.