Java：从文本文件中获取整数后，扫描仪显示零

Question

I am using Scanner class to fetch Integers from my Integers.txt file. The bug is that I am not getting the exact Integers in Array. I get zeros only. Although, the summation is correct when I try to find Minimum value, I get 0 as Minimum value. What am I doing wrong?

This is the code:

/**
* Program to take various integers from users as input and stores them 
in file called "Integers.txt"
* (a) The process should continue until user enters -9999 as input
* (b) Calculate summation of all the numbers available in Integers.txt
* (c) Find Maximum & Minimum Numbers from File
* (d) Sort the numbers available in the Integers.txt into 
    "SortedIntegers.txt"
* (e) Sort the Integers.txt file  
**/

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

class Exercise8{
    public static void main(String args[]){
        Scanner scan = new Scanner(System.in);
        // Code snippet to create a file named Integers.txt
        try{
            File integerFile = new File("Integers.txt");
            integerFile.createNewFile();    
        }catch(Exception e){
    }


    int choice = 0;
    do{
        System.out.println("\nSelect an Operation: ");
        System.out.println("(1) Input Integers in Integers.txt");
        System.out.println("(2) Calculate sum of all the numbers available in Integers.txt");
        System.out.println("(3) Find Maximum & Minimum of Numbers from File");
        System.out.println("(4) Sort the Integers.txt");
        System.out.println("(5) Sort the Numbers into SortedIntegers.txt");     
        try{
        System.out.print("\nEnter Choice: ");
        choice = scan.nextInt();
        switch(choice){
                case 1: 
                    try{
                        FileWriter fstreamIntegers = new FileWriter("Integers.txt");
                        BufferedWriter outIntegers = new BufferedWriter(fstreamIntegers);       
                        //Scanner scan = new Scanner(System.in);
                        System.out.print("How many numbers do you want to enter?: ");
                        int num = scan.nextInt();
                        String integers[] = new String[num+1];

                        for(int i = 0; i < integers.length; i++){
                            integers[i] = scan.nextLine();
                            outIntegers.write(integers[i]+"\n");
                        }
                        outIntegers.close();
                    }catch(IOException e){
                        e.printStackTrace();
                    }
                    break;

                case 2:                     
                    try{
                        File integerFile = new File("Integers.txt");                        
                        Scanner inFile = new Scanner(integerFile);
                        //int size = inFile.nextInt();
                        int[] arrIntegers = new int[(int)integerFile.length()];
                        int i = 0;
                        while(inFile.hasNextInt()){
                            arrIntegers[i++] = inFile.nextInt();
                            /*inFile.next();
                            if(inFile.hasNextInt()){

                            }*/
                        }
                        int sum = 0;
                        for(int j = 0; j < arrIntegers.length; j++){
                            System.out.println(arrIntegers[j]);
                            sum += arrIntegers[j];
                        }
                        System.out.println("\nSum of the integers present in Integers.txt is " + sum);

                    }catch(Exception e){
                    }                       
                    break;

                    case 3:                     
                    try{
                        File integerFile = new File("Integers.txt");                        
                        Scanner inFile = new Scanner(integerFile);
                        int[] arrIntegers = new int[(int)integerFile.length()];
                        int i = 0;
                        while(inFile.hasNextInt()){
                            arrIntegers[i++] = inFile.nextInt();
                            /*if(!inFile.hasNextInt()){
                                inFile.next();
                            }*/
                        }

                        int max = arrIntegers[0];               
                        for(int j = 0; j < arrIntegers.length; j++){
                            if(max < arrIntegers[j]){
                                max = arrIntegers[j];
                            }
                        }
                        System.out.println("\nMaximum number out of numbers present in Integers.txt is " + max);

                        int min = arrIntegers[0];               
                        for(int j = 0; j < arrIntegers.length; j++){
                            if(min > arrIntegers[j]){
                                min = arrIntegers[j];
                            }
                        }
                        System.out.println("\nMinimum number out of numbers present in Integers.txt is " + min);

                    }catch(Exception e){
                    }                       
                    break;

                default: 
                    if(choice == -9999){
                    }else{
                        System.out.println("\n*****Enter Valid Choice!*****");
                    }
        }
        }catch(InputMismatchException e){
            System.out.print("\n*****Enter Valid Choice!*****");
            scan.next();                
        }               
    }while(choice != -9999);
    scan.close();
  }
}

This is the Integers.txt file

1
2
3
4
5

The output:

Output Image

Answer 1

int[] arrIntegers = new int[(int)integerFile.length()]; creates an array of size the number of bytes of the file integerFile .

Then the while loop executes i++ at each iteration so that when the following for loop iterating over j executes System.out.println(arrIntegers[i]); (note i , and not j ), i points to an index that has never been set in the array, therefore returning 0 , the default int value.

That is why 0 is printed at each iteration while the sum is correct!

Answer 2

You might have created Integers.txt in wrong path.. First try running with option 1 first and enter the 5 values 1, 2, 3, 4, 5 so that file is created from the program at the same path where you are trying to read... Next try running option 2, you will see the sum getting correctly displayed..

Try printing the file path using below code and check what values this file has.

System.out.println("File path :"+ integerFile.getAbsolutePath());

Answer 3

You have referred i in place of j in your for loop for case '2' . So change your for loop to as follows for case '2' :

for(int j = 0; j < arrIntegers.length; j++){
    System.out.println(arrIntegers[j]);
    sum += arrIntegers[j];
}

Answer 4

I was supposed to be using ArrayList for dynamic array. I am posting the code snippet of case 2 here which worked for me.

case 2:                     
                    try{
                        File integerFile = new File("Integers.txt");                        
                        Scanner inFile = new Scanner(integerFile);
                        //int size = inFile.nextInt();
                        List<Integer> listIntegers = new ArrayList<>();
                        /*for(int i = 0; i < upperBound; i++) {
                            sum.add(i);
                        }
                        // necessary to convert back to Integer[]
                        Integer[] sumArray = sum.toArray(new Integer[0]);*/
                        //int[] arrIntegers = new int[(int)integerFile.length()];
                        int i = 0;
                        while(inFile.hasNextInt()){
                            //arrIntegers[i++] = inFile.nextInt();
                            i = inFile.nextInt();
                            listIntegers.add(i);
                            i++;
                            /*inFile.next();
                            if(inFile.hasNextInt()){

                            }*/
                        }
                        Integer[] arrIntegers = listIntegers.toArray(new Integer[0]);
                        int sum = 0;
                        for(int j = 0; j < arrIntegers.length; j++){
                            System.out.println(arrIntegers[j]);
                            sum += arrIntegers[j];
                        }
                        System.out.println("\nSum of the integers present in Integers.txt is " + sum);

                    }catch(Exception e){
                    }                       
                    break;