如何知道BufferedReader是否与DataInputStream链接？

Question

In a method I need a BufferedReader wrapping a DataInputStream as a parameter. I want to declare the method as this :

public void firstPass(BufferedReader inStream){ // some code ... }

But I don't know how I can check whether inStream is wrapping a DataInputStream.

I've tried

public static void firstPass(BufferedReader inStream){
    if (inStream instanceof DataInputStream){

    }       
}

but the code can't compile (Eclispe does not accept the code : "Incompatible conditional operand types BufferedReader and DataInputStream").

---

Why this need ? Because I want to use with the same variable inStream :

• the method readLine() from BufferedReader
• the method readDouble() from DataInputStream

So I need a stream which chains both classes.

I'm programming with Java 7 JDK.

Could someone help me please ? Thanks in advance.

Answer 1

A DataInputStream can never be a instance of BufferedReader - they are both in separate class hierarchies.

A BufferedReader wraps another Reader, not a Stream.

You can bridge from Streams to Readers using an InputStreamReader .

Reading doubles and lines from the same Reader doesn't really makes sense - one is raw binary data, the other is character data. Maybe you need to read a textual encoding of the doubles, and parse this using Double.parseDouble(text) .

Answer 2

A. It is not possible to accomplish what you are trying to accomplish with maybe adding a flag to your method that is accepting the bufferedReader argument

B. It's not clear how you are passing the DataInputStream to a BufferedReader (probably through InputStreamReader right?) But in any case it seems wrong that you are using BufferedReader and DataInputStream together. BufferedReader is going to use your DataInputStream like a plain InputStream, so I don't know why you would have put the DataInputStream around it

Answer 3

DataInputStream class isn't subtype of class BufferedReader

class DataInputStream extends FilterInputStream implements DataInput {}

class BufferedReader extends Reader {}

More info:

• http://docs.oracle.com/javase/7/docs/api/java/io/DataInputStream.html
• http://docs.oracle.com/javase/7/docs/api/java/io/BufferedReader.html

Answer 4

BufferedReader不是DataInputStream的子类，因此您的错误是合乎逻辑的......

Answer 5

BufferedReaders are for text data and DataInputStream is for binary data. You would never wrap one with the other unless you like confusing people.

You can use a DataInputStream to wrap a BufferedInputStream (It wouldn't make any sense to wrap it the other way)

You can wrap a BufferedReader around an InputStreamReader, but there is no simple way to determine this has been done.

You could write

BufferedReader br = new BufferedReader(new FileReader(name));

But you would have to use the reflections library to determine what the BufferedReader wraps.