Java - ObjectOutputStream writeDouble(double val) method

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Description

The Java ObjectOutputStream writeDouble(double val) method writes a 64 bit double.

• Writes the double value as 8 bytes (64 bits) to the stream in big-endian order.

• It does not serialize a Double object - just writes the binary representation.

• It's part of the DataOutput interface, which ObjectOutputStream implements.

Declaration

Following is the declaration for java.io.ObjectOutputStream.writeDouble(double val) method.

public void writeDouble(double val)

Parameters

• val − The double value to be written.

Return Value

This method does not return a value.

Exception

• IOException − If I/O errors occur while writing to the underlying stream.

Example - Usage of ObjectOutputStream writeDouble(double val) method

The following example shows the usage of ObjectOutputStream writeDouble(double val) method.

ObjectOutputStreamDemo.java

package com.tutorialspoint;

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

public class ObjectOutputStreamDemo {
   public static void main(String[] args) {
      double d = 1.59875d;
      
      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.writeDouble(d);
         oout.writeDouble(9673.49764d);

         // close the stream
         oout.close();

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

         // read and print what we wrote before
         System.out.println("" + ois.readDouble());
         System.out.println("" + ois.readDouble());
      } catch (Exception ex) {
         ex.printStackTrace();
      }
   }
}

Output

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

1.59875
9673.49764

Example - Write and read a single double value

The following example shows the usage of ObjectOutputStream writeDouble(double val) method. We're writing a temperature value (36.6) using writeDouble(), and reading it back

ObjectOutputStreamDemo.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 ObjectOutputStreamDemo {
   public static void main(String[] args) {
      String filename = "double1.bin";

      // Write a single double value
      try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(filename))) {
         double temp = 36.6;
         oos.writeDouble(temp);
         System.out.println("Wrote double: " + temp);
      } catch (IOException e) {
         e.printStackTrace();
      }

      // Read the value back
      try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename))) {
         double value = ois.readDouble();
         System.out.println("Read double: " + value);
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Wrote double: 36.6  
Read double: 36.6

Example - Write multiple double values to simulate a dataset

The following example shows the usage of ObjectOutputStream writeDouble(double val) method. We're writing several double values representing prices, and read them back.

ObjectOutputStreamDemo.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 ObjectOutputStreamDemo {
   public static void main(String[] args) {
      String filename = "double_prices.bin";
      double[] prices = {19.99, 5.75, 99.0, 149.49};

      // Write all prices using writeDouble
      try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(filename))) {
         for (double price : prices) {
            oos.writeDouble(price);
         }
         System.out.println("Wrote " + prices.length + " double values.");
      } catch (IOException e) {
         e.printStackTrace();
      }

      // Read them back
      try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename))) {
         System.out.println("Read values:");
         for (int i = 0; i < prices.length; i++) {
            double value = ois.readDouble();
            System.out.println(" - " + value);
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Wrote 4 double values.
Read values:
 - 19.99
 - 5.75
 - 99.0
 - 149.49