Question

Java!!!

Write a program that takes a file name as its command line argument. It assumes the file is a binary data file and checks the first 4 bytes of the file to see whether they contain the integer −889275714. It outputs “yes” or “no” or an error message if there was an IOException generated. (Trivia question: Why test for that particular value? Hint: Try it on several .class files.)

Answer 1

Answer:

Code:

I run some class files and exe files it satisfies for the class file

Output:

Raw_code:

import java.io.*; //importing io module for file methods
public class Bin_check {
   public static void main(String args[]){  
       try{
          String file = args[0];   //taking file name as command line argument
            FileInputStream fin=new FileInputStream(file);
            DataInputStream dis = new DataInputStream(fin); //getting data of a file
            int i = -889275714; // given value to check..
            if (i == dis.readInt()) //readInt() takes first 4 bytes of data
            {
               System.out.println("Yes"); //prints if it equal
            }
            else{
               System.out.println("No"); // prints if not equal
            }
          
            fin.close();  
       }
       //If file is not found Here printing exception
       catch(Exception e){System.out.println("There was an IO Exception Generated");}  
    }  
}

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Answer 2

pythonCopy codeimport sysdef check_integer_in_file(file_name):    try:        with open(file_name, "rb") as file:
            first_four_bytes = file.read(4)
            integer_value = int.from_bytes(first_four_bytes, byteorder='big', signed=True)            if integer_value == -889275714:                print("yes")            else:                print("no")    except FileNotFoundError:        print("Error: File not found.")    except IOError:        print("Error: IO Exception occurred.")if __name__ == "__main__":    if len(sys.argv) != 2:        print("Usage: python program_name.py file_name")    else:
        file_name = sys.argv[1]
        check_integer_in_file(file_name)

Trivia Answer: The value −889275714 is a specific signature called the "magic number" that appears at the beginning of compiled Java class files. The Java compiler inserts this signature to mark the file as a valid Java class file. By checking for this value, we can quickly identify whether a given file is a valid compiled Java class file or not. If the first four bytes contain this value, it is likely that the file is a Java class file. This technique is often used in various tools and utilities to identify and validate Java class files.

Answer 3

In Java, you can use the following program to check the first 4 bytes of a binary data file and see if they contain the integer -889275714. It will output "yes" if the value is found, "no" if the value is not found, or an error message if there was an IOException generated while reading the file.

javaCopy codeimport java.io.DataInputStream;import java.io.FileInputStream;import java.io.IOException;public class BinaryFileChecker {    public static void main(String[] args) {        if (args.length != 1) {
            System.err.println("Usage: java BinaryFileChecker <file_name>");            return;
        }        String fileName = args[0];        try (DataInputStream dataInputStream = new DataInputStream(new FileInputStream(fileName))) {            int firstFourBytes = dataInputStream.readInt();            if (firstFourBytes == -889275714) {
                System.out.println("yes");
            } else {
                System.out.println("no");
            }
        } catch (IOException e) {
            System.err.println("Error reading the file: " + e.getMessage());
        }
    }
}

Explanation:The program takes a file name as a command line argument and attempts to open the file as a binary data file using a DataInputStream. It then reads the first 4 bytes of the file using the readInt() method, which reads an integer (4 bytes) from the input stream.

The program checks if the integer value read from the file matches the value -889275714. If it does, it outputs "yes," indicating that the value is found. If the value does not match, it outputs "no."

The significance of testing for the value -889275714 lies in its use in Java class files. In Java bytecode, this value is known as the "magic number." It is a constant value that appears at the beginning of all valid Java class files. By checking for this specific value, the program can determine if the file follows the class file format used by Java.