DataInputStream.read() 与 DataInputStream.readFully()

Question

Im making a simple TCP/IP Socket app

Whats the different between doing this:

DataInputStream in = new DataInputStream(clientSocket.getInputStream());

byte[] buffer = new byte[100];
in.readFully(buffer);

versus doing this:

DataInputStream in = new DataInputStream(clientSocket.getInputStream());

byte[] buffer = new byte[100];
in.read(buffer);

I had a look at the documentation, they have the same exact description. readFully() and read() So can I assume its the same thing?

Answer 1

The Javadoc for DataInput.readFully(byte[] b) states:

Reads some bytes from an input stream and stores them into the buffer array b . The number of bytes read is equal to the length of b .

The Javadoc for DataInputStream.read(byte[] b) states:

Reads some number of bytes from the contained input stream and stores them into the buffer array b . The number of bytes actually read is returned as an integer. This method blocks until input data is available, end of file is detected, or an exception is thrown .

Basically, readFully() will read exactly b.length bytes, whereas read() will read up to b.length , maybe less, whatever is available from the input stream.

Answer 2

Using read you need to check return value to know how many bytes have been really read

byte[] buffer = new byte[100];
if (in.read(buffer) < 100){
   // fail
   }

instead with readFully a IOException will be thrown if the 100 bytes could not be read, don't need to check return value, simplify a bit.