Java.io.RandomAccessFile Class Method | Set 1

Last Updated : 23 May, 2019

Java.io.RandomAccessFile Class provides a way to random access files using reading and writing operations. It works like an array of byte storted in the File. Declaration :

public class RandomAccessFile
   extends Object
      implements DataOutput, DataInput, Closeable

Methods of RandomAccessFile Class :

read() : java.io.RandomAccessFile.read() reads byte of data from file. The byte is returned as an integer in the range 0-255

Syntax :
public int read()
Parameters : 
--------
Return  :
reads byte of data from file, -1 if end of file is reached.

read(byte[] b) java.io.RandomAccessFile.read(byte[] b) reads bytes upto b.length from the buffer.

Syntax :
public int read(byte[] b)
Parameters : 
b : buffer to be read
Return  :
byte of data from file upto b.length, -1 if end of file is reached.

read((byte[] b, int offset, int len) : java.io.RandomAccessFile.read((byte[] b, int offset, int len) reads bytes initialising from offset position upto b.length from the buffer.

Syntax :
public int read(byte[] b, int offset, int len)
Parameters : 
b : buffer to read
offset : starting position to read
len : max no of bytes to read
Return  :
reads bytes initialising from offset position upto b.length from the buffer.

readBoolean() : java.io.RandomAccessFile.readBoolean() reads a boolean from the file.

Syntax :
public final boolean readBoolean()
Parameters : 
------
Return  :
boolean value

readByte() : java.io.RandomAccessFile.readByte() reads a signed eight-bit value from file, start reading from the File Pointer.
```
Syntax :
public final byte readByte()
Parameters : 
-------
Return  :
signed eight-bit value from file
```
readChar() : java.io.RandomAccessFile.readChar() reads a character from the file, start reading from the File Pointer.
```
Syntax :
public final char readChar()
Parameters : 
-------
Return  :
character from the file.
```
readDouble() : java.io.RandomAccessFile.readDouble() reads a double value from the file, start reading from the File Pointer.
```
Syntax :
public final double readDouble()
Parameters : 
------
Return  :
reads a double value from the file.
```
readFloat() : java.io.RandomAccessFile.readFloat() reads a float value from the file, start reading from the File Pointer.
```
Syntax :
public final double readFloat()
Parameters : 
------
Return  :
reads a float value from the file.
```

readFully(byte[] b) : java.io.RandomAccessFile.readFully(byte[] b) reads bytes upto b.length from the buffer, start reading from the File Pointer.

Syntax :
public final void readFully(byte[] b)
Parameters : 
b : buffer to be read
Return  :
reads bytes initialising from offset position upto b.length from the buffer

readInt() : java.io.RandomAccessFile.readInt() reads a signed 4 bytes integer from the file, start reading from the File Pointer.

Syntax :
reads a signed 4 bytes integer from the file
Parameters : 
-----
Return  :
reads a signed 4 bytes integer from the file

readFully(byte[] b, int offset, int len) : java.io.RandomAccessFile.readFully(byte[] b, int offset, int len) reads bytes initialising from offset position upto b.length from the buffer, start reading from the File Pointer.

Syntax :
public final void readFully(byte[] b, int offset, int len)
Parameters : 
b : buffer to read
offset : starting position to read
len : max no of bytes to read
Return  :
bytes initialising from offset position upto b.length from the buffer

readLong() : java.io.RandomAccessFile.readLong() reads a signed 64 bit integer from the file, start reading from the File Pointer.
```
Syntax :
public final long readLong()
Parameters : 
-------
Return  :
signed 64 bit integer from the file
```

Java

// Java Program illustrating use of io.RandomAccessFile class methods
// read(), read(byte[] b), readBoolean(), readByte(), readInt()
// readFully(byte[] b, int off, int len), readFully(), readFloat()
// readChar(), readDouble(),

import java.io.*;
public class NewClass
{
    public static void main(String[] args)
    {
        try
        {
            double d = 1.5;
            float f = 14.56f;

            // Creating a new RandomAccessFile - "GEEK"
            RandomAccessFile geek = new RandomAccessFile("GEEK.txt", "rw");

            // Writing to file
            geek.writeUTF("Hello Geeks For Geeks");

            // File Pointer at index position - 0
            geek.seek(0);

            // read() method :
            System.out.println("Use of read() method : " + geek.read());

            geek.seek(0);

            byte[] b = {1, 2, 3};
            
            // Use of .read(byte[] b) method :
            System.out.println("Use of .read(byte[] b) : " + geek.read(b));

            // readBoolean() method :
            System.out.println("Use of readBoolean() : " + geek.readBoolean());

            // readByte() method :
            System.out.println("Use of readByte() : " + geek.readByte());

            geek.writeChar('c');
            geek.seek(0);

            // readChar() :
            System.out.println("Use of readChar() : " + geek.readChar());

            geek.seek(0);
            geek.writeDouble(d);
            geek.seek(0);

            // read double
            System.out.println("Use of readDouble() : " + geek.readDouble());

            geek.seek(0);
            geek.writeFloat(f);
            geek.seek(0);

            // readFloat() :
            System.out.println("Use of readFloat() : " + geek.readFloat());

            geek.seek(0);
            // Create array upto geek.length
            byte[] arr = new byte[(int) geek.length()];
            // readFully() :
            geek.readFully(arr);
            
            String str1 = new String(arr);
            System.out.println("Use of readFully() : " + str1);

            geek.seek(0);
            
            // readFully(byte[] b, int off, int len) :
            geek.readFully(arr, 0, 8);
            
            String str2 = new String(arr);
            System.out.println("Use of readFully(byte[] b, int off, int len) : " + str2);
        }
        catch (IOException ex)
        {
            System.out.println("Something went Wrong");
            ex.printStackTrace();
        }
    }
}

Output :

Use of read() method : 0
Use of .read(byte[] b) : 3
Use of readBoolean() : true
Use of readByte() : 108
Use of readChar() : c
Use of readDouble() : 1.5
Use of readFloat() : 14.56
Use of readFully() : Geeks For Geeks
Use of readFully(byte[] b, int off, int len) : Geeks For Geeks

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