PushBackInputStream and DataInputStream, how to push back a double?

Question

If I want to read ahead a byte,and push it back if it is not '<',I can do it like this:

PushbackInputStream pbin=new PushbackInputStream(new FileInputStream("1.dat"));
int b = pbin.read();
if(b!='<')
    pbin.unread(b);

But if I want to push back a double that I read from DataInputStream,what shall i do? For example:

PushbackInputStream pbin1=null;
DataInputStream din=new DataInputStream(
            pbin1=new PushbackInputStream(
                        new FileInputStream("1.dat")
                    )
        );
double d = din.readDouble();
pbin1.unread(d);

The last line pbin1.unread(d); can not be compiled,because the PushbackInputStream can not push back a double,how can I convent the double to byte array?or any other way?

Answer 1

You can't push back a double that way. Method DataInputStream.readDouble() reads 8 bytes to create a double, you can't just pass a double to PushbackInputStream.unread() and expect him to know how to deal with.

To achieve what you want the solution is simple:

PushbackInputStream pbin1=new PushbackInputStream(new FileInputStream("1.dat"));
DataInputStream din=new DataInputStream(pbin1);

double d = din.readDouble(); // Get the double out of the stream
byte[] doubleAsBytes = new byte[8];
ByteBuffer.wrap(doubleAsBytes).putDouble(d); // transform the double into his byte representation
pbin1.unread(doubleAsBytes); // push back the bytes