Java - ObjectInputStream readLong() method

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Description

The Java ObjectInputStream readLong() method reads a 64 bit long.

Declaration

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

public long readLong()

Parameters

NA

Return Value

This method returns the read 64 bit long.

Exception

• EOFException − If end of file is reached.

• IOException − If an I/O error has occurred.

Example - Usage of ObjectInputStream readLong() method

The following example shows the usage of Java ObjectInputStream readLong() method.

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class ObjectInputStreamDemo {
   public static void main(String[] args) {
      long l = 397638763597645l;
      
      try {
         // create a new file with an ObjectOutputStream
         FileOutputStream out = new FileOutputStream("test.txt");
         ObjectOutputStream oout = new ObjectOutputStream(out);

         // write something in the file
         oout.writeLong(l);
         oout.writeLong(8364876387634l);
         oout.flush();

         // create an ObjectInputStream for the file we created before
         ObjectInputStream ois = new ObjectInputStream(new FileInputStream("test.txt"));

         // read and print a long
         System.out.println("" + ois.readLong());

         // read and print a long
         System.out.println("" + ois.readLong());
      } catch (Exception ex) {
         ex.printStackTrace();
      }
   }
}

Output

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

397638763597645
8364876387634

Example - Reading Fields along with Missing Fields

The following example shows the usage of Java ObjectInputStream readLong() method. This example demonstrates how to write a long value to a file using ObjectOutputStream and then read it back using ObjectInputStream.

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class ObjectInputStreamDemo {
   public static void main(String[] args) {
      String filename = "longData.bin";

      // Writing a long value to a file
      try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(filename))) {
         long num = 123456789L;
         oos.writeLong(num);
         System.out.println("Long value written: " + num);
      } catch (IOException e) {
         e.printStackTrace();
      }

      // Reading the long value from the file
      try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename))) {
         long readNum = ois.readLong();
         System.out.println("Long value read: " + readNum);
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Long value written: 123456789
Long value read: 123456789

Explanation

• The program writes a long value (123456789L) to a binary file (longData.bin) using ObjectOutputStream.

• It then reads the same long value back using ObjectInputStream.readLong().

• This ensures that the stored value can be retrieved correctly.

Example - Reading multiple long values from a file

The following example shows the usage of Java ObjectInputStream readLong() method. This example writes multiple long values to a file and reads them back sequentially.

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.EOFException;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class ObjectInputStreamDemo {
   public static void main(String[] args) {
      String filename = "multiLongData.bin";

      // Writing multiple long values to a file
      try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(filename))) {
         long[] numbers = {100000L, 200000L, 300000L};

         for (long num : numbers) {
            oos.writeLong(num);
         }
         System.out.println("Long values written.");
      } catch (IOException e) {
         e.printStackTrace();
      }

      // Reading multiple long values from the file
      try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename))) {
         while (true) {
            try {
               long readNum = ois.readLong();
               System.out.println("Long value read: " + readNum);
            } catch (EOFException e) {
               break; // End of file reached
            }
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Long values written.
Long value read: 100000
Long value read: 200000
Long value read: 300000

Explanation

• Writes three long values (100000, 200000, 300000) to a file.

• Reads them one by one using readLong(), maintaining the original order.

• Prints each long value, confirming correct serialization and deserialization.