Reading data from file using FIleInputStream

1.Reading the data from a file:

• FileInputStream class is used to read data from a file.
• It is two step process.

1. Create  FileInputStream class object by using its available constructors.
2. Then call read() method on this object till control reach end of file.

• Means read() method must be called in loop, because it returns only one byte at a time .
• Hence it must be called in loop for each byte available in the file till it returns "-1".
• It returns  -1 if control reached end of the file.

FileInputStream class has below constructors to create its object:

1.  public FileInputStrean(String name) throws FileNotFoundException
2.  public FileInputStream(File file)  throws FileNotFoundException
3.  public FileInputStream(FileDescriptor fd)

Rule:

• To Create FileInputStream class object the file must be with the passed argument name . else this constructor throws java.io.FileNotFoundException.
• FileInputStream  class constructor throws FileNotFoundException in below situations.

• If the file is not existed with the passed name.
• Passed file name is a directory rather than is a regular file.
• If file does not have reading permissions.

 Java Program to read data from a file:

1.  Create a file with name test.txt. with text "hello world" this is for example you can write any text.
2. Creating stream object connecting to test.txt file.
   FileInputStream fis= new FileInputStream("test.txt");
3. Reading all bytes from the file till control reaches end of file.
   int i=fis.read();
4. Printing returned character.
   System.out.println(i);

Program #1: 

1. package com.instanceofjava;
2.  
3. import java.io.FileInputStream;
4. import java.io.FileNotFoundException;
5. import java.io.IOException;
6.  
7. public class FISDemo {
8.  
9.  public static void main(String[] args) throws FileNotFoundException, IOException
10. {
11.  
12.       FileInputStream fis= new FileInputStream("E:\\test.txt");
13.  
14.         int i;
15.         while((i=fis.read())!=-1){
16.            System.out.println((char)i);
17.         }
18.  
19.     }
20. }

Output:

1. h
2. e
3. l
4. l
5. o
6.  
7. w
8. o
9. r
10. l
11. d

Program #2: Using read() method

1. package com.instanceofjava;
2.  
3. import java.io.FileInputStream;
4. import java.io.FileNotFoundException;
5. import java.io.IOException;
6.  
7. public class FISDemo {
8.  
9.  public static void main(String[] args) throws FileNotFoundException, IOException
10. {
11.  
12.       FileInputStream fis= new FileInputStream("E:\\test.txt");
13.  
14.        byte[] b=new byte[fin.available()];
15.  
16.        // Read data into the array
17.         fin.read(b);
18.         for (int i = 0; i < b.length; i++) {
19.  
20.             System.out.println((char)b[i]);
21.  
22.         }
23.  
24.     }
25. }

Output:

1. h
2. e
3. l
4. l
5. o
6.  
7. w
8. o
9. r
10. l
11. d

Program #3: Using read(destination, start-index, last-index) method

1. package com.instanceofjava;
2.  
3. import java.io.FileInputStream;
4. import java.io.FileNotFoundException;
5. import java.io.IOException;
6.  
7. public class FISDemo {
8.  
9.  public static void main(String[] args) throws FileNotFoundException, IOException
10. {
11.  
12.       FileInputStream fis= new FileInputStream("E:\\test.txt");
13.  
14.       byte b1[]=new byte[fin.available()];
15.       fin.read(b1,0,b1.length);
16.  
17.                     for(int i=0;i<b1.length;i++)
18.                     {
19.                     System.out.print((char)b1[i]);
20.                     }
21.  
22.     }
23. }

Output:

1. hello world