JIYIK CN >

In this tutorial, we will see how to whiledetect EOF( End OF File) in Java using a loop. We will also discuss developing a program that continues reading content until it reaches the end of a file.

From a programming perspective, EOF is a special type used by developers to continuously read input, whether it is from a file or a keyboard console. This process continues until there is no more data to retrieve.

It is worth mentioning here that the data in the file can be modified or changed at any time. Therefore, it is practically impossible to apply a sentinel control loop on that file.

Therefore, we strongly recommend that you always use file closing loops to mitigate the potential threat of the above issues.

In the following code example, we use the keyboard as the input source.

package sampleProject;
import java.util.*;
import java.util.Scanner;
public class Codesample {
  static Scanner console = new Scanner(System.in);
  public static void main(String[] args) {
    int total_ages = 0;
    int age;
    while (console.hasNext()) {
      age = console.nextInt();
      total_ages = total_ages + age;
    }

    System.out.println("Total ages are:" + total\_ages);
  }
}

Output:

99
90
88
Ko
Exception in thread "main" java.util.InputMismatchException
at java.base/java.util.Scanner.throwFor(Scanner.java:939)
at java.base/java.util.Scanner.next(Scanner.java:1594)
at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
at sampleProject/sampleProject.Codesample.main(Codesample.java:15)

We start by declaring and initializing an object of the Scanner class. After that, I have declared some other variables to use in our code.

You may have noticed that we use console.hasNext()as the loop iteration condition. We already know that the console is an object of our input class Scanner.

On the other hand, hasNext()is a predefined method in the input class Scanner. This expression returns true only if there is an integer input. Otherwise, it returns false.

Compile this code on your own and see the output. It is clear from the output that our program continues to read the data until we provide the wrong input type. In this case, the program throws an input mismatch exception.

File as input source

In another example, we use an end-of-file controlled while loop to continuously read data from a file.

Suppose we want Students\_Result.txtto read all the data from the file . The file contains the names of students followed by their exam scores.

Our goal in this program is to output a file that displays the student's name, test score, and grade.

package sampleProject;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.PrintWriter;
import java.util.*;
import java.util.Scanner;
public class Codesample {
  static Scanner console = new Scanner(System.in);
  public static void main(String[] args) throws FileNotFoundException {
    // declare file name as an input object
    Scanner inputFile = **new** Scanner(**new** FileReader("Students\_Result.txt"));
    // declare the output object that stores data we want to display
    PrintWriter outputFile = **new** PrintWriter("Students\_Record.txt");
    // Declare variable to store first name and last name
    String firstName, lastName;
    // declare variable to store score
    double score;
    // declare variable to store student's grad
    char grade = ' ';
    // declare and initialize counter variable
    int counter = 0;
    // continue reading data from the file until the loop reaches end of file
    while (inputFile.hasNext()) {
      // read first name from the provided file
      firstName = inputFile.next();
      // read last name from the file
      lastName = inputFile.next();
      // read score of the students from the filee
      score = inputFile.nextDouble();
      // increment counter variable
      counter++;
      // To evaluate grade of the students, we are using the switch statemet
      switch ((int) score / 10) {
        case 0:
        case 1:
        case 2:
        case 3:
        case 4:
        case 5:
          grade = 'F';
          break;
        case 6:
          grade = 'D';
          break;
        case 7:
          grade = 'C';
          break;
        case 8:
          grade = 'B';
          break;
        case 9:
        case 10:
          grade = 'A';
          break;
        default:
          outputFile.println("Your score does not meet our criteria");
      }
      //   Display retrieved data using the outputFile object we have declared earlier
      outputFile.println(firstName + " " + lastName + " " + score + " " + grade);
    }
    // If no data is found in the output file
    if (counter == 0)
      outputFile.println("There is not data in your input file");
    // close output file upon reading all the data from it.
    outputFile.close();
  }
}

Output:

Waleed Ahmed 89.5 B
Bob Alice 90.0 A
Khan Arshad 100.0 A
Waqas Jameed 65.5 D
Danish Taimoor 70.5 C
Muaz Junaid 80.5 B
John Harris 88.0 B

Compile and run this program on your system to see what happens.