Java.io.DataOutputStream in Java - GeeksforGeeks

06 Oct, 2021
A data output stream lets an application write primitive Java data types to an output stream in a portable way. An application can then use a data input stream to read the data back in. Let us do discuss the constructor of this class prior to moving ahead to the methods of this class. 
Constructor: DataOutputStream (OutputStream out)
Creates a new data output stream to write data to the specified underlying output stream. Now let us discuss important methods of this class prior to implementing the same. 
Method 1: void flush() 
Flushes this data output stream. 
Syntax: 
public void flush() throws IOException
Note: It do overrides the flush() method in class FilterOutputStream
Exception thrown: IOException
Method 2: size()
Returns the current value of the counter written, the number of bytes written to this data output stream so far
Syntax:
public final int size()
Return Type: An integer value of the written field
Method 3: write () 
Writes len bytes from the specified byte array starting at offset off to the underlying output stream. 
Syntax:
void write (byte[] b, int off, int len)
Parameters: 
Byte array
int off
Length of the byte array
Return Type: void 
Method 4: 
Syntax:
public void write(byte[] b, int off,int len)
Note: It overrides write() method in FilterOutputStream class.
Parameters:
The data
The start offset in the data
The number of bytes to write
Exceptions: IOException
Method 5: void write (int b): 
Writes the specified byte (the low eight bits of argument b) to the underlying output stream. 
Syntax:
public void write(int b)
throws IOException
ReturnType: Void
Parameters:  The byte to be written
Method 6: writeBoolean()
Writes a boolean to the underlying output stream as a 1-byte value.
Syntax:
void writeBoolean (boolean v) 
Return Type: Void
Parameters: Boolean value
Method 7: writeBoolean()
Syntax:
public final void writeBoolean(boolean v)
throws IOException 
Parameters: Boolean value to be written.
Throws: IOException
Method 8: writeByte()
Writes out a byte to the underlying output stream as a 1-byte value. 
Syntax:
public final void writeByte(int v)
throws IOException 
Parameters: A byte value to be written 
Exception Thrown:  IOException
Method 9: writeChar()
Writes a char to the underlying output stream as a 2-byte value, high byte first.
Syntax:
public final void writeChar(int v)
throws IOException
Parameters:  A character value to be written.
Exception: IOException 
Method 10: void writeDouble (double v)
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. 
Syntax:
public final void writeDouble(double v)
throws IOException
Parameters: A double value to be written
Exception thrown: IOException
Method 11: writeFloat (float v)
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, MSB first. 
Syntax:
public final void writeFloat(float v)
throws IOException
Return Type: Void
Parameters: A float value to be written.
Exception thrown: IOException
Method 12: writeInt()
Writes an int to the underlying output stream as four bytes, high byte first. 
Syntax:
public final void writeInt(int v)
throws IOException
Parameters: An int to be written.
Return Type: Void
Exceptions Thrown: Writes an int to the underlying output stream as four bytes, high byte first. 
Method 13: writeLong()
Writes a long to the underlying output stream as eight bytes, high byte first. 
Syntax :
public final void writeLong(long v)
throws IOException
Parameters:  Long to be written.
Throws: IOException
Method 14: writeShort(): 
Writes a short to the underlying output stream as two bytes, high byte first. 
Return Type: Void
Parameter: A short to be written
Syntax :
public final void writeShort(int v)
throws IOException
Method 15: writeUTF (String str) 
Writes a string to the underlying output stream using modified UTF-8 encoding in a machine-independent manner. 
Parameter: A string to be written
Return Type:  Void 
Exception Thrown: IOException
Note: There are certain important points to be remembered as listed: 
DataOutputStream and DataInputStream are often used together.
When a DataOutputStream is closed (by calling close( )), the underlying stream specified by out is also closed automatically.
There is no longer any explicit close() method call. The try-with-resources construct takes care of that.
Example:
// Java Program to Demonstrate DataOutputStream // Importing required classesimport java.io.*; // Main class// DataOutputStreamDemoclass GFG {        // Main driver method        public static void main(String args[]) throws IOException {                // Try block to check for exceptions                // Writing the data using DataOutputStream                try ( DataOutputStream dout =                                                new DataOutputStream(new FileOutputStream("file.dat")) ) {                        dout.writeDouble(1.1);                        dout.writeInt(55);                        dout.writeBoolean(true);                        dout.writeChar('4');                }                 catch (FileNotFoundException ex) {                        System.out.println("Cannot Open the Output File");                        return;                }                 // Reading the data back using DataInputStream                try ( DataInputStream din =                                                new DataInputStream(new FileInputStream("file.dat")) ) {                        double a = din.readDouble();                        int b = din.readInt();                         boolean c = din.readBoolean();                        char d = din.readChar();                         System.out.println("Values: " + a + " " + b + " " + c + " " + d);                }                 // Catch block to handle FileNotFoundException                catch (FileNotFoundException e) {                        System.out.println("Cannot Open the Input File");                        return;                }        }}
Output:
Values: 1.1 55 true 4
Note: The above program uses try-with-resources so do it require JDK 7 or later.
This article is contributed by Nishant Sharma. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. 
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