File i/o

Question 1

How do you read a file line by line in Java?

Answer 1

Use a Scanner object with a File.

Scanner sc = new Scanner(new File(“input.txt”));
while (sc.hasNextLine()) {
System.out.println(sc.nextLine());
}
sc.close();

Question 2

How do you write to a file in Java?

Answer 2

Use PrintWriter or FileWriter.

PrintWriter writer = new PrintWriter(“output.txt”);
writer.println(“Hello, World!”);
writer.close();

Question 3

How do you check if a file exists in Java?

Answer 3

se the exists() method from the File class.

File file = new File(“input.txt”);
if (file.exists()) {
System.out.println(“File exists”);
}

Question 4

How do you read words from a file into an array in Java?

Answer 4

Use ArrayList to store words.

ArrayList<String> words = new ArrayList<>();
Scanner sc = new Scanner(new File("words.txt"));
while (sc.hasNextLine()) {
words.add(sc.nextLine());
}
sc.close();</String>

Question 5

How do you count the number of lines in a file?

Answer 5

Loop through the file with while (sc.hasNextLine())

Question 6

Write a snippet to write “Hello” to a file.

Answer 6

PrintWriter writer = new PrintWriter(“output.txt”);
writer.println(“Hello”);
writer.close();

Question 7

How do you handle exceptions when working with files?

Answer 7

Use a try-catch block

Question 8

What method checks if the file can be written to?

Answer 8

canWrite() method of the File class

Question 9

How do you reverse the lines of a file?

Answer 9

Read lines into a list, reverse the list using Collections.reverse(), and write back to a file.

Question 10

What is the difference between FileReader and FileWriter?

Answer 10

FileReader is for reading files; FileWriter is for writing files.

Question 11

How do you close a file after reading?

Answer 11

Call sc.close() for a Scanner object.