Table of Contents
DataInputStream in Java
Java DataInputStream is a class that we use to read primitive data type values. We can use this stream along with other input streams like FileInputStream to read the data. Since it reads data as numbers instead of bytes, we call it as DataInputStream. It contains only a single constructor that accepts an InputStream as a parameter.
DataInputStream di = new DataInputStream(InputStream in);
Methods of Java DataInputStream
Below are the methods that the DataInputStream class supports for write and other operations.
| Methods | Description |
|---|---|
| int available() | Returns the estimated number of remaining bytes available to read |
| void close() | Closes the input stream |
| void mark(int readLimit) | Marks the current position in the input stream |
| boolean markSupported() | Checks if the input stream supports mark() and reset() methods |
| int read() | Reads the next byte of data in the input stream |
| int read(byte[] b) | Reads an array of bytes of data from the input stream |
| int read(byte[] b, int off, int len) | Reads len bytes of data from the input stream starting from the offset position |
| boolean readBoolean() | Reads the boolean value from the stream |
| byte readByte() | Reads the next byte of data from the input stream |
| char readChar() | Reads the next char of data from the input stream |
| double readDouble() | Reads the next double data from the input stream |
| float readFloat() | Reads the next float data from the input stream |
| void readFully(byte[] b) | Reads all bytes of data from the input stream and stores in the buffer array b |
| void readFully(byte[] b, int off, int len) | Reads len bytes of data from the input stream starting from the offset into the byte buffer array |
| int readInt() | Reads the next integer data from the input stream |
| String readLine() | Reads a line of string from the input stream |
| long readLong() | Reads a long data from the input stream |
| byte[] readNBytes(int len) | Reads the specific length of bytes from the input stream and stores into the buffer |
| int readNBytes(byte[] b, int off, int len) | Reads len number of bytes from the input stream from the offset position and stores in buffer array b |
| short readShort() | Reads a short data from the input stream |
| int readUnsignedByte() | Reads the next unsigned bytes of data from the input stream |
| int readUnsignedShort() | Reads the next unsigned short data from the input stream |
| String readUFT() | Reads the unicode form of data from the input stream |
| long skip(long n) | Skips and discards n number of bytes to read from the input stream |
| int skipBytes(int n) | Skips and discards the specific number of bytes during the read operation |
Example
The below example uses the read() method of the DataInputStream class to read the data from the input file. We can check the available number of bytes to read using the available() method.
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.DataInputStream;
public class DataInputStreamDemo {
public static void main(String[] args) throws IOException {
FileInputStream fi = new FileInputStream("InputFile.txt");
DataInputStream di = new DataInputStream(fi);
System.out.println("Available number of bytes to read: " + di.available());
int a;
while((a=di.read()) != -1)
System.out.print((char)a);
}
}
Available number of bytes to read: 37 This is an example of DataInputStream
Example: DatatInputStream different read methods
The below example demonstrates the various read methods to read data from the file using the DataInputStream class.
The readUFT() method is for reading the Unicode format data, readInt() method for integer value, readChar() for character data, readBoolean() for boolean value, readDouble() for double data, readFloat() for float value and readLong() for long value.
There are corresponding write methods in the DataOutputStream class to write these values which we will see in detail in the next tutorial.
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.DataInputStream;
import java.io.DataOutputStream;
public class DataInputStreamDemo {
public static void main(String[] args) throws IOException {
FileInputStream fi = new FileInputStream("OutputFile.txt");
DataInputStream di = new DataInputStream(fi);
FileOutputStream fo = new FileOutputStream("OutputFile.txt");
DataOutputStream dos = new DataOutputStream(fo);
dos.writeUTF("DataInputStream");
dos.writeInt(25);
dos.writeChar('d');
dos.writeBoolean(false);
dos.writeDouble(233.34);
dos.writeFloat(555.55f);
dos.writeLong(8888888);
System.out.println("Available number of bytes to read: " + di.available());
System.out.println("Read UFT: " + di.readUTF());
System.out.println("Read int: " + di.readInt());
System.out.println("Read char: " + di.readChar());
System.out.println("Read boolean: " + di.readBoolean());
System.out.println("Read double: " + di.readDouble());
System.out.println("Read float: " + di.readFloat());
System.out.println("Read Long: " + di.readLong());
di.close();
fi.close();
dos.close();
fo.close();
}
}
Available number of bytes to read: 44 Read UFT: DataInputStream Read int: 25 Read char: d Read boolean: false Read double: 233.34 Read float: 555.55 Read Long: 8888888
Example: Read the specific length of data using DataInputStream
We can also read the specific length of data using the DataInputStream class in Java. The below example shows how to read the text of length 8 from the input file. We are allocating only 12 bytes and hence the remaining 4 bytes are filled with *.
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.DataInputStream;
public class DataInputStreamDemo {
public static void main(String[] args) throws IOException {
FileInputStream fi = new FileInputStream("InputFile.txt");
DataInputStream di = new DataInputStream(fi);
byte[] b = new byte[12];
int a = di.read(b, 0, 8);
for(byte by : b) {
char ch = (char)by;
if(by == 0)
ch = '*';
System.out.print(ch);
}
di.close();
fi.close();
}
}
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Example: DataInputStream skip() method
The below example demonstrates how to use the skip() method that skips or discards specific characters during the read operation. Here, we are discarding the first 4 characters and hence reads only from the 5th character.
import java.io.*;
public class SkipDISDemo {
public static void main(String[] args) throws IOException {
FileInputStream fi;
try {
fi = new FileInputStream("InputFile.txt");
DataInputStream di = new DataInputStream(fi);
di.skip(4);
int a = 0;
while((a=di.read()) != -1)
System.out.print((char)a);
di.close();
fi.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
}
is an example of DataInputStream