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Java - DataOutputStream writeDouble(double value) method

Description

The Java DataOutputStream writeDouble(double value) method method converts the double argument to a long using the doubleToLongBits method in class Double, and then writes that long value to the underlying output stream as an 8-byte quantity, high byte first. If no exception is thrown, the counter written is incremented by 8.

Declaration

Following is the declaration for java.io.DataOutputStream.writeDouble(double value) method −

 public final void writeDouble(double value)

Parameters

v − a double value to be written to the output stream.

Return Value

This method does not return any value.

Exception

IOException − If an I/O error occurs.

Example - Usage of DataOutputStream writeDouble(double value) method

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

Once double array is fully written into the stream, we've flushed 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 readDouble() method, we're reading every value as double. Finally we're closing all the streams.

DataOutputStreamDemo.java

 package com.tutorialspoint; 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 DataOutputStreamDemo { public static void main(String[] args) throws IOException { InputStream is = null; DataInputStream dis = null; FileOutputStream fos = null; DataOutputStream dos = null; double[] dbuf = {65.56,66.89,67.98,68.82,69.55,70.37}; try { // create file output stream fos = new FileOutputStream("test.txt"); // create data output stream dos = new DataOutputStream(fos); // for each byte in the buffer for (double d:dbuf) { // write double to the data output stream dos.writeDouble(d); } // force bytes to the underlying stream dos.flush(); // create file input stream is = new FileInputStream("test.txt"); // create new data input stream dis = new DataInputStream(is); // read till end of the stream while(dis.available()>0) { // read double double c = dis.readDouble(); // 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 −

 65.56 66.89 67.98 68.82 69.55 70.37

Example - Usage of DataOutputStream writeDouble(double value) method

Then double array is iterated to write double values using writeDouble() method to the dataoutputstream. Once double 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 readDouble() method, we're reading every value as double. Finally we're closing all the streams.

DataOutputStreamDemo.java

 package com.tutorialspoint; 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 DataOutputStreamDemo { public static void main(String[] args) throws IOException { InputStream is = null; DataInputStream dis = null; FileOutputStream fos = null; DataOutputStream dos = null; double[] dbuf = {65.56,66.89,67.98,68.82,69.55,70.37}; try { // create file output stream fos = new FileOutputStream("test.txt"); // create data output stream dos = new DataOutputStream(fos); // close the stream dos.close(); // for each byte in the buffer for (double d:dbuf) { // write double to the data output stream dos.writeDouble(d); } // force bytes to the underlying stream dos.flush(); // create file input stream is = new FileInputStream("test.txt"); // create new data input stream dis = new DataInputStream(is); // read till end of the stream while(dis.available()>0) { // read double double c = dis.readDouble(); // 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.FileOutputStream.writeBytes(Native Method)	at java.base/java.io.FileOutputStream.write(FileOutputStream.java:367)	at java.base/java.io.DataOutputStream.writeDouble(DataOutputStream.java:259)	at com.tutorialspoint.DataOutputStreamDemo.main(DataOutputStreamDemo.java:32) Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.io.InputStream.close()" because "is" is null	at com.tutorialspoint.DataOutputStreamDemo.main(DataOutputStreamDemo.java:62)

As underlying stream FileOutputStream is not supporting write to stream after closing it, we get exception in program execution.

Example - Writing and Reading a Double Using writeDouble(double value)

The following example shows the usage of Java DataOutputStream writeDouble(double value) method.

DataOutputStreamDemo.java

 package com.tutorialspoint; import java.io.DataOutputStream; import java.io.DataInputStream; import java.io.FileOutputStream; import java.io.FileInputStream; import java.io.IOException; public class DataOutputStreamDemo { public static void main(String[] args) { try { // Create a DataOutputStream to write to a file FileOutputStream fileOutput = new FileOutputStream("output.dat"); DataOutputStream dataOutput = new DataOutputStream(fileOutput); // Write double values to the file dataOutput.writeDouble(3.14159); // Pi approximation dataOutput.writeDouble(9.81); // Gravity acceleration (m/s) dataOutput.writeDouble(-1234.567);// Negative double value // Close the output stream dataOutput.close(); System.out.println("Double values successfully written to output.dat"); // Read the doubles back FileInputStream fileInput = new FileInputStream("output.dat"); DataInputStream dataInput = new DataInputStream(fileInput); // Read and print the double values System.out.println("First double: " + dataInput.readDouble()); // 3.14159 System.out.println("Second double: " + dataInput.readDouble()); // 9.81 System.out.println("Third double: " + dataInput.readDouble()); // -1234.567 // Close the input stream dataInput.close(); } catch (IOException e) { e.printStackTrace(); } } }

Output

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

 Double values successfully written to output.dat First double: 3.14159 Second double: 9.81 Third double: -1234.567

Explanation

Writing Double values

writeDouble(3.14159) − Writes 3.14159 as 8 bytes.
writeDouble(9.81) − Writes 9.81 as 8 bytes.
writeDouble(-1234.567) − Writes -1234.567 as 8 bytes.

Reading Double values

readDouble() reads back 8 bytes at a time and reconstructs them into double values.

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