Java - DataInputStream readLong() method

Description

The Java DataInputStream readLong() method reads eight input bytes are returns a long value.

Declaration

Following is the declaration for java.io.DataInputStream.readLong() method −

public final long readLong()

Parameters

NA

Return Value

This method returns 8 bytes of input stream, longerpreted as a long value.

Exception

  • IOException − If an I/O error occurs or the stream is closed.

  • EOFException − If the input stream reaches the end before the method invocation.

Example 1

The following example shows the usage of Java DataInputStream readLong() method. We've created InputStream, DataInputStream, FileOutputStream and DataOutputStream reference. A long[] buf is initialized with some long values. A FileOutputStream object is created with a File. Then DataOutputStream is initialized with FileOutputStream object created before. Then long array is iterated to write long values to the dataoutputstream.

Once long arrays is fully written into the stream, we've flush the stream to store the values in the file. Now using FileInputStream and DataInputStream, we're reading the file written earlier. Now we're checking if DataInputStream object has data using available() method. Then using readLong() method, we're reading every value as long. Finally we're closing all the streams.

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
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;
      FileOutputStream fos = null;
      DataOutputStream dos = null;
      long[] buf = {128,250,430,520,820};
      
      try {
         // create file output stream
         fos = new FileOutputStream("F:\\test.txt");
         
         // create data output stream
         dos = new DataOutputStream(fos);
         
         // for each byte in the buffer
         for (long d:buf) {
         
            // write long to the data output stream
            dos.writeLong(d);         
         }
         
         // force bytes to the underlying stream
         dos.flush();
         
         // create file input stream
         is = new FileInputStream("F:\\test.txt");
         
         // create new data input stream
         dis = new DataInputStream(is);
         
         // read till end of the stream
         while(dis.available()>0) {
         
            // read long
            long c = dis.readLong();
            
            // print
            System.out.print(c + " ");
         }
         
      } catch(Exception e) {
         // if any I/O error occurs
         e.printStackTrace();
      } finally {
         // releases all system resources from the streams
         if(is!=null)
            is.close();
         if(dos!=null)
            is.close();
         if(dis!=null)
            dis.close();
         if(fos!=null)
            fos.close();
      }
   }
}

Output

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

128 250 430 520 820

Example 2

The following example shows the usage of Java DataInputStream readLong() method. We've created InputStream, DataInputStream, FileOutputStream and DataOutputStream reference. A long[] buf is initialized with some long values. A FileOutputStream object is created with a File. Then DataOutputStream is initialized with FileOutputStream object created before. Then long array is iterated to write long values to the dataoutputstream. Once long arrays is fully written into the stream, we've flush the stream to store the values in the file.

Now using FileInputStream and DataInputStream, we're reading the file written earlier. Now we're checking if DataInputStream object has data using available() method. Then using readLong() method, we're reading every value as long. Now as a special case, we're closing the stream before reading the values to see if this methods throw exception or not. As a result, we can see the available() method throws the exception.

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
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;
      FileOutputStream fos = null;
      DataOutputStream dos = null;
      long[] buf = {128,250,430,520,820};
      
      try {
         // create file output stream
         fos = new FileOutputStream("F:\\test.txt");
         
         // create data output stream
         dos = new DataOutputStream(fos);
         
         // for each byte in the buffer
         for (long d:buf) {
         
            // write long to the data output stream
            dos.writeLong(d);         
         }
         
         // force bytes to the underlying stream
         dos.flush();
         
         // create file input stream
         is = new FileInputStream("F:\\test.txt");
         
         // create new data input stream
         dis = new DataInputStream(is);

         // close the streams
         is.close();
         dis.close();
         
         // read till end of the stream
         while(dis.available()>0) {
         
            // read long
            long c = dis.readLong();
            
            // print
            System.out.print(c + " ");
         }
         
      } catch(Exception e) {
         // if any I/O error occurs
         e.printStackTrace();
      } finally {
         // releases all system resources from the streams
         if(is!=null)
            is.close();
         if(dos!=null)
            is.close();
         if(dis!=null)
            dis.close();
         if(fos!=null)
            fos.close();
      }
   }
}

Output

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

java.io.IOException: Stream Closed
	at java.base/java.io.FileInputStream.available0(Native Method)
	at java.base/java.io.FileInputStream.available(FileInputStream.java:330)
	at java.base/java.io.FilterInputStream.available(FilterInputStream.java:167)
	at DataInputStreamDemo.main(DataInputStreamDemo.java:44)

Example 3

The following example shows the usage of Java DataInputStream readLong() method. We've created InputStream, DataInputStream, FileOutputStream and DataOutputStream reference. A long[] buf is initialized with some long values. A FileOutputStream object is created with a File. Then DataOutputStream is initialized with FileOutputStream object created before. Then long array is iterated to write long values to the dataoutputstream. Once long arrays is fully written into the stream, we've flush the stream to store the values in the file.

Now using FileInputStream and DataInputStream, we're reading the file written earlier. Now we're checking if DataInputStream object has data using available() method. Then using readLong() method, we're reading every value as long. Now as a special case, we're reading bytes after all bytes are read using readLong() method. As a result, we can see the readLong() throws an EOFException.

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
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;
      FileOutputStream fos = null;
      DataOutputStream dos = null;
      long[] buf = {128,250,430,520,820};
      
      try {
         // create file output stream
         fos = new FileOutputStream("F:\\test.txt");
         
         // create data output stream
         dos = new DataOutputStream(fos);
         
         // for each byte in the buffer
         for (long d:buf) {
         
            // write long to the data output stream
            dos.writeLong(d);         
         }
         
         // force bytes to the underlying stream
         dos.flush();
         
         // create file input stream
         is = new FileInputStream("F:\\test.txt");
         
         // create new data input stream
         dis = new DataInputStream(is);
         
         // read till end of the stream
         while(dis.available()>0) {
         
            // read long
            long c = dis.readLong();
            
            // print
            System.out.print(c + " ");
         }
		 System.out.print(dis.readLong());
         
      } catch(Exception e) {
         // if any I/O error occurs
         e.printStackTrace();
      } finally {
         // releases all system resources from the streams
         if(is!=null)
            is.close();
         if(dos!=null)
            is.close();
         if(dis!=null)
            dis.close();
         if(fos!=null)
            fos.close();
      }
   }
}

Output

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

128 250 430 520 820 java.io.EOFException
	at java.base/java.io.DataInputStream.readFully(DataInputStream.java:202)
	at java.base/java.io.DataInputStream.readLong(DataInputStream.java:421)
	at DataInputStreamDemo.main(DataInputStreamDemo.java:48)
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