According to the documentation, BufferedReader(Reader) uses a default buffer size, while the second constructor, BufferedReader(Reader, int) allows         
        
The default buffer size is 8192 characters
http://developer.android.com/reference/java/io/BufferedReader.html
BufferedReader(Reader in) Constructs a new BufferedReader, providing in with a buffer of 8192 characters.
Besides this documentation, I've extraced the rt.jar archive, and decompiled the BufferedReader.class from java.io.* using JD-GUI, this is what I found in the class definition:
private static int defaultCharBufferSize = 8192;