Java IO & Generics Detailed Notes

1. What is File?

A File in Java represents a physical file or directory path in the system. It does not contain file data but provides methods to manipulate files.

Features:

• Used to create, delete, and rename files
• Works with both files and directories
• Platform independent path handling

File f = new File("sample.txt");
System.out.println(f.exists());

2. How to Read File

Java provides multiple ways to read files depending on performance and requirement.

Common Classes:

• Scanner (easy but slower)
• FileReader (character based)
• BufferedReader (fast and efficient)

File f = new File("sample.txt");
Scanner sc = new Scanner(f);
while(sc.hasNextLine()){
    System.out.println(sc.nextLine());
}

3. Data Stream Types

A stream is a sequence of data. Java IO streams are used to read and write data.

Main Types:

• Byte Stream: Handles binary data
• Character Stream: Handles text data

4. Byte Streams

Byte streams are used for handling binary data like images, audio, and video files.

Classes:

• FileInputStream
• FileOutputStream

FileInputStream fis = new FileInputStream("a.txt");
int i;
while((i=fis.read())!=-1){
    System.out.print((char)i);
}

5. Character Streams

Character streams are used for reading and writing text data. They handle Unicode characters.

Classes:

• FileReader
• FileWriter

FileReader fr = new FileReader("a.txt");
int i;
while((i=fr.read())!=-1){
    System.out.print((char)i);
}

6. Further Categories of Streams

1. Buffered Streams

Improve performance by reducing IO operations.

2. Data Streams

Used to read/write primitive data types.

3. Object Streams

Used for serialization (saving objects).

BufferedReader br = new BufferedReader(new FileReader("a.txt"));
System.out.println(br.readLine());

7. File Writing

Used to store data permanently into files.

Important Points:

• Always close the stream
• Use BufferedWriter for better performance

FileWriter fw = new FileWriter("a.txt");
fw.write("Hello Java");
fw.close();

8. Random Access File

Allows reading and writing at any position in a file.

Advantages:

• Direct access to data
• Efficient for large files

RandomAccessFile raf = new RandomAccessFile("a.txt","rw");
raf.writeUTF("Hello");
raf.seek(0);
System.out.println(raf.readUTF());

9. Purpose of Generics

Generics enable type-safe and reusable code.

Advantages:

• Compile-time error checking
• No need for type casting
• Improves code readability

class Box<T>{
 T value;
}

10. Generic Class

A class that works with different data types using type parameters.

class Data<T>{
 T data;
 Data(T d){data=d;}
}

11. Generic Method

A method that can operate on different types.

public static <T> void print(T[] arr){
 for(T i:arr) System.out.println(i);
}