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Q and A 2025_iii

What is a Stream in Java?

A stream is a sequence of data (bytes or characters) that can be read from or written to.

Difference between InputStream and OutputStream.

InputStream: reads bytes from a source. OutputStream: writes bytes to a destination.

Difference between Reader and Writer classes.

  • Reader: reads character streams.
  • Writer: writes character streams.

    • Difference between byte streams and character streams.

  • Byte streams (InputStream/OutputStream) handle raw bytes.
  • Character streams (Reader/Writer) handle characters and are suitable for text.

    • What are the main subclasses of InputStream and OutputStream?

  • FileInputStream, BufferedInputStream, DataInputStream (InputStream)
  • FileOutputStream, BufferedOutputStream, DataOutputStream (OutputStream)

    • What are the main subclasses of Reader and Writer?

  • FileReader, BufferedReader, InputStreamReader (Reader)
  • FileWriter, BufferedWriter, PrintWriter (Writer)

    • How to read a file using FileInputStream? 

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

    How to write data using FileOutputStream? 

    FileOutputStream fos = new FileOutputStream("file.txt");
String data = "Hello";
fos.write(data.getBytes());
fos.close();

    How to read a file using FileReader? 

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

    How to write to a file using FileWriter? 

    FileWriter fw = new FileWriter("file.txt");
fw.write("Hello World");
fw.close();

    What is BufferedInputStream and BufferedOutputStream?

    Streams that buffer input/output to improve performance.

    What is BufferedReader and BufferedWriter?

    Readers/Writers that buffer characters for faster I/O, and allow line-by-line reading/writing.

    Difference between buffered and unbuffered streams.

    Buffered streams use memory buffers for efficiency; unbuffered streams read/write directly.

    What is DataInputStream and DataOutputStream?

    Streams to read/write Java primitive types (int, double, etc.) in a machine-independent way.

    How to use ObjectInputStream and ObjectOutputStream?

    For reading/writing serializable objects
    ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("obj.dat"));
    oos.writeObject(obj);
    oos.close();

    Difference between FileInputStream and FileReader.

    FileInputStream: byte stream; FileReader: character stream. Use Reader for text files.

    Write purpose of flush() method.

    Ensures buffered data is written to the destination immediately.

    How to close a stream properly?

    Using close() method or try-with-resources to automatically close streams.

    What is the File class?

    Represents file and directory pathnames in Java.

    How to create a new file? 

    File file = new File("file.txt");
file.createNewFile();

    How to delete a file? 

    File file = new File("file.txt");
file.delete();

    How to check if a file exists? 

    File file = new File("file.txt");
file.exists();

    Get file name, path, and length.

    file.getName(); file.getPath(); file.length();

    How to list all files in a directory? 

    File dir = new File("folder");
String[] files = dir.list();

    How to create a directory? 

    File dir = new File("folder");
dir.mkdir();

    How to check if File is a file or directory?

    file.isFile(); file.isDirectory();

    How to rename a file? 

    File oldFile = new File("old.txt");
File newFile = new File("new.txt");
oldFile.renameTo(newFile);

    How to read file line by line using BufferedReader? 

    BufferedReader br = new BufferedReader(new FileReader("file.txt"));
String line;
while((line = br.readLine()) != null) {
    System.out.println(line);
}
br.close();

    How to write to file line by line using BufferedWriter? 

    BufferedWriter bw = new BufferedWriter(new FileWriter("file.txt"));
bw.write("Line1");
bw.newLine();
bw.write("Line2");
bw.close();

    How to use Scanner to read data from a file? 

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