Java.io.DataInputStream.read() Method

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Description

The java.io.DataInputStream.read(byte[] b, int off, int len) method reads len bytes from the contained input stream and allocate them in the buffer b starting at b[off]. The method is blocked until input data is available, an exception is thrown or end of file is detected.

Declaration

Following is the declaration for java.io.DataInputStream.read(byte[] b, int off, int len) method:

public final int read(byte[] b, int off, int len)

Parameters

  • b - the byte[] into which the data is read from the input stream.

  • off - the start offset in the b[].

  • len - the maximum number of bytes read.

Return Value

Total number of bytes read, else -1 if the stream has reached the end.

Exception

  • IOException -- if an I/O error occurs, the first byte cannot be read, or close() is invoked before this method.

  • NullPointerException -- if b is null.

  • IndexOutOfBoundsException -- if len is greater than b.length - off, off is negative, or len is negative

Example

The following example shows the usage of java.io.DataInputStream.read(byte[] b, int off, int len) method.

package com.tutorialspoint;

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

public class DataInputStreamDemo {
   public static void main(String[] args) throws IOException {
      
      InputStream is = null;
      DataInputStream dis = null;
      
      try{
         // create input stream from file input stream
         is = new FileInputStream("c:\\test.txt");
         
         // create data input stream
         dis = new DataInputStream(is);
         
         // count the available bytes form the input stream
         int count = is.available();
         
         // create buffer
         byte[] bs = new byte[count];
         
         // read len data into buffer starting at off
         dis.read(bs, 4, 3);
         
         // for each byte in the buffer
         for (byte b:bs)
         {
            // convert byte into character
            char c = (char)b;
            
            // empty byte as char '0'
            if(b ==0)
               c='0';
            
            // print the character
            System.out.print(c);
         }
      }catch(Exception e){
         // if any I/O error occurs
         e.printStackTrace();
      }finally{
         
         // releases any associated system files with this stream
         if(is!=null)
            is.close();
         if(dis!=null)
            dis.close();
      }   
   }
}

Assuming we have a text file c:/test.txt, which has the following content. This will file will be used as an input for our example program:

ABCDEFGH

Let us compile and run the above program, this will produce the following result:

0000ABC0



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