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Java - DataOutputStream writeFloat(float value) method

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Description

The Java DataOutputStream writeFloat(float value) method converts the float argument to an int using the floatToIntBits method in class Float, and then writes that int value to the underlying output stream as a 4-byte quantity, high byte first. If no exception is thrown, the counter written is incremented by 4.

Declaration

Following is the declaration for java.io.DataOutputStream.writeFloat(float value) method −

public final void writeFloat(float v)

Parameters

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

Return Value

The method returns the value of the written field.

Exception

IOException − If an I/O error occurs.

Example - Usage of DataOutputStream writeFloat(float value) method

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

Once float 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 readFloat() method, we're reading every value as float. 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;
      float[] dbuf = {65.56f,66.89f,67.98f,68.82f,69.55f,70.37f};
      
      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 (float d:dbuf) {
         
            // write float to the data output stream
            dos.writeFloat(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 float
            float c = dis.readFloat();
            
            // 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 writeFloat(float value) method

As a special case, we're closing the stream before writing any value to check if it supports writing values after closing it. Then float array is iterated to write float values using writeFloat() method to the dataoutputstream.

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;
      float[] dbuf = {65.56f,66.89f,67.98f,68.82f,69.55f,70.37f};
      
      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 (float d:dbuf) {
         
            // write float to the data output stream
            dos.writeFloat(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 float
            float c = dis.readFloat();
            
            // 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.write(Native Method)
	at java.base/java.io.FileOutputStream.write(FileOutputStream.java:318)
	at java.base/java.io.DataOutputStream.writeInt(DataOutputStream.java:197)
	at java.base/java.io.DataOutputStream.writeFloat(DataOutputStream.java:242)
	at DataOutputStreamDemo.main(DataOutputStreamDemo.java:30)
Exception in thread "main" java.lang.NullPointerException
	at DataOutputStreamDemo.main(DataOutputStreamDemo.java:60)

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

Example - Usage of DataOutputStream writeFloat(float value) method

The following example shows the usage of Java DataOutputStream writeFloat(float value) method.

DataOutputStreamDemo.java

package com.tutorialspoint;

import java.io.DataOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class DataOutputStreamDemo {
   public static void main(String[] args) {
      try (FileOutputStream fos = new FileOutputStream("output.dat");
         DataOutputStream dos = new DataOutputStream(fos)) {

         float value = 3.14f; // Floating-point number
         dos.writeFloat(value); // Writes 3.14 as 4 bytes in IEEE 754 format

         System.out.println("Float value written successfully.");

      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Float value written successfully.

Explanation

FileOutputStream− Creates a binary file "output.dat" for writing data.
DataOutputStream− Wraps FileOutputStream to enable writing primitive types.
writeFloat(float value) Method− Converts the float 3.14f into IEEE 754 32-bit floating-point format. Writes the 4 bytes to the file.

Binary Representation (output.dat)

The float 3.14f is stored in IEEE 754 format

01000000  10010001  11101011  10000101

java_io_dataoutputstream.htm

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