扫描仪提示用户输入数字

Question

Here are the instructions I'm trying to follow:

Write a method called negative sum that accepts a scanner reading input from a file containing a series of integers., and a print message to the console indicating whether the sum starting from the first number is ever negative.You should alse return true if a negative sum can be reached and false if not. for example, suppose the file contains the 38 4 19 -27 -15 -3 4 19 38 your method would consider the sum of just number (38) , the first two numbers ( 38 + 4) the firs three number ( 38 + 4 + 19) and so on to the asnd . none of thes sume is negative so the method would produce the following output and return false : No negative numbers.

If the file instead contains 14 7 -10 9 -18 -10 17 42 98 the method finds that a negative sum of -8 is reached after adding the first six numbers. it should output the following to the console and return true: sum of -8 after 6 steps.

This is what I have so far. I'm just having trouble adding the scanner to prompt the user for the numbers.

import java.io.*;
import java.util.*;

public class NegativeSum{
    public static void main (String [] args )
    throws FileNotFoundException{


        negativesum();


        }//end of amin

public static boolean negativesum()
throws FileNotFoundException{


     File file = new File ("negativeSum.txt");
    Scanner input =  new Scanner (file);

    int sum=0;
    int count = 0;

    while ( input.hasNextInt()){
        int next =input.nextInt();
        sum+=next;
        count++;

        if ( sum<0){
            System.out.println("sum of " + sum + " after " + count + "steps" );
            return true;
            }

        }///end of while
    System.out.println("no negative sum ");
    return false;




    }//end of metho d

}//end of main

Answer 1

The only serious mistake I see in your implementation (vs. your problem statement) is that your method should receive a Scanner as input (eg accepts a scanner ) -

public static boolean negativeSum(Scanner input) {
  if (input == null) {
    // Handle null - e.g. no value
    return false;
  }
  int sum = 0;
  int count = 0;

  while (input.hasNextInt()) {
    int next = input.nextInt();
    sum += next;
    count++;

    if (sum < 0) {
      System.out.println("sum of " + sum + " after "
          + count + " steps");
      return true;
    }
  }// /end of while
  System.out.println("no negative sum");
  return false;
}

Answer 2

I don't see anything in your problem description that asks you to prompt the user for numbers. It appears that your code already meets the stated requirements of the assignment.

If you did want to do that, though:

• System.in is an InputStream representing standard input.
• The Scanner(InputStream) constructor creates a Scanner that reads from the specified InputStream .

I'll leave it as an exercise to you to figure out how to put the two together. :)