Question

I am given an input file, P1input.txt and I have to write code to find the min and max, as well as prime and perfect numbers from the input file. P1input.txt contains a hundred integers. Why doesn't my code compile properly to show me all the numbers? It just stops and displays usage: C:\> java Project1 P1input.txt 1 30

import java.io.*; // BufferedReader
import java.util.*; // Scanner to read from a text file

public class Project1
{
   public static void main (String args[]) throws Exception // we NEED this 'throws' clause
   {
       // ALWAYS TEST FIRST TO VERIFY USER PUT REQUIRED CMD ARGS
       if (args.length < 3)
       {
           System.out.println("\nusage: C:\\> java Project1 P1input.txt 1 30\n\n");
           // i.e. C:\> java Project1.txt P1input.txt 1 30
           System.exit(0);
       }

       String infileName = args[0]; // no need to convert, just copy into infileName
       int lo = Integer.parseInt( args[1] ); // conver to int then store into lo
       int hi = Integer.parseInt( args[2] ); // conver to int then store into hi

       // STEP #1: OPEN THE INPUT FILE AND COMPUTE THE MIN AND MAX. NO OUTPUT STATMENTS ALLOWED
       Scanner infile = new Scanner( new File(infileName) );
       int min,max;
       min=max=infile.nextInt(); // WE ASSUME INPUT FILE HAS AT LEAST ONE VALUE
       while ( infile.hasNextInt() )
       {
           // YOUR CODE HERE FIND THE MIN AND MAX VALUES OF THE FILE
           // USING THE LEAST POSSIBLE NUMBER OF COMPARISONS
           // ASSIGN CORRECT VALUES INTO min & max INTHIS LOOP.
           // MY CODE BELOW WILL FORMAT THEM TO THE SCREEN
           // DO NOT WRITE ANY OUTPUT TO THE SCREEN
           int num = infile.nextInt();

           if(num < min)
           min = num;

           if(num > max)
           max = num;
       }

       System.out.format("min: %d max: %d\n",min,max); // DO NOT REMOVE OR MODIFY IN ANY WAY

       // STEP #2: DO NOT MODIFY THE REST OF MAIN. USE THIS CODE AS IS
       // WE ARE TESTING EVERY NUMBER BETWEEN LO AND HI INCLUSIVE FOR
       // BEING PRIME AND/OR BEING PERFECT
       for (int i=lo ; i<=hi ; ++i)
       {
           System.out.print( i );
           if ( isPrime(i) ) System.out.print( " prime ");
           if ( isPerfect(i) ) System.out.print( " perfect ");
           System.out.println();
       }
   } // END MAIN

   // *************** YOU FILL IN THE METHODS BELOW **********************

   // RETURNs true if and only if the number passed in is perfect
   static boolean isPerfect( int n )
   {
       int sum = 0;
       for (int i =1; i <= n/2; i++)
       {
           if(n % i == 0)
               sum += i;
       }

       if (sum == n)
           return true;

       else
           return false; // (just to make it compile) YOU CHANGE AS NEEDED
   }
   // RETURNs true if and only if the number passed in is prime
   static boolean isPrime( int n )
   {
       for (int f = 2; f <= n/2; f++)
       {
       if (n % f == 0)
           return false;

       }
               return true; // (just to make it compile) YOU CHANGE AS NEEDED
   }
}

Answer 1

// Project1.java

import java.io.*; // BufferedReader
import java.util.*; // Scanner to read from a text file

public class Project1
{
   public static void main (String args[]) throws Exception // we NEED this 'throws' clause
   {
       // ALWAYS TEST FIRST TO VERIFY USER PUT REQUIRED CMD ARGS
       if (args.length < 3)
       {
           System.out.println(" usage: C:\> java Project1 <input file name> <lo> <hi> ");
           // i.e. C:> java Project1.txt P1input.txt 1 30
           System.exit(0);
       }
       // grab args[0] and store into a String var named infileName

    final String infileName = args[0];

       // grab args[1] and conver to int then store into a var named lo

    final int lo = Integer.parseInt(args[1]);

       // grab args[2] and conver to int then store into a var named hi

    final int hi = Integer.parseInt(args[2]);

       // STEP #1: OPEN THE INPUT FILE AND COMPUTE THE MIN AND MAX. NO OUTPUT STATMENTS ALLOWED
       Scanner infile = new Scanner( new File(infileName) );
       int min,max;
       min=max=infile.nextInt(); // WE ASSUME INPUT FILE HAS AT LEAST ONE VALUE
       while ( infile.hasNextInt() )
       {
        int next = infile.nextInt();
        if (next < min){
          min = next;
        }
        if (next > max){
          max = next;
        }
       }
       System.out.format("min: %d max: %d ",min,max); // DO NOT REMOVE OR MODIFY IN ANY WAY

       // STEP #2: DO NOT MODIFY THE REST OF MAIN. USE THIS CODE AS IS
       // WE ARE TESTING EVERY NUMBER BETWEEN LO AND HI INCLUSIVE FOR
       // BEING PRIME AND/OR BEING PERFECT
       for ( int i=lo ; i<=hi ; ++i)
       {
           System.out.print( i );
           if ( isPrime(i) ) System.out.print( " prime ");
           if ( isPerfect(i) ) System.out.print( " perfect ");
           System.out.println();
       }
   } // END MAIN

   // *************** YOU FILL IN THE METHODS BELOW **********************

   // RETURNs true if and only if the number passed in is perfect
   static boolean isPerfect( int n )
{
    int total = 0;
    for (int i = 1; i < n; i++){
      if ((n % i) == 0){
        total += i;
      }
    }
    if (total == n){
      return true;
    }
    return false;
   }
   // RETURNs true if and only if the number passed in is prime
   static boolean isPrime( int n )
   {
    if (n == 1){
      return false;
    }
    for (int i = 1; i < n; i++){
      if ((n % i) == 0 && (n / i) != 1 && (n / i) != n){
        return false;
      }
    }
       return true; // (just to make it compile) YOU CHANGE AS NEEDED
   }
} // END Project1 CLASS