Java- Printing an Original Array while Performing Operations on an Array Copy

[smilesofmiles]

Hello mathhelpboards community! Please help! Thank you. :-)

I need my code to print out the user's original array that is to say the numbers in the way the user entered them. I tried making a copy of the original array and then did all of the arithmetic on it. I sorted the array copy in another method and used it to find the averages. I expected that this would allow me to keep the original numbers in tact. However, when I call the last method PrintResults to print the original array I get back the sorted array (the array copy). How do I fix this?

package calcavgdropsmallest;import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.Collections;
import java.util.List;

public class CalcAvgDropSmallest {
    
   private static DecimalFormat df2 = new DecimalFormat(".00");

   public static ArrayList<Double> getArrayNumbers(){
       Scanner input = new Scanner(System.in);
       
       System.out.println("Please enter five to ten numbers separated by spaces on one line.");
       
       ArrayList<Double> userNumbers = new ArrayList<>();
       ArrayList<Double> numCopy = new ArrayList<>(userNumbers); //Created a copy of the array.
       
       String numbers = input.nextLine();
       String[] strHolder = numbers.split("\\s+"); 
       
       for(int counter = 0; counter < strHolder.length; counter++){
           userNumbers.add(counter, Double.parseDouble(strHolder[counter])); //Adding numbers to the array
        } 
       
       return userNumbers;
    }
   
   public static int getLowestNumber(){
       Scanner input = new Scanner(System.in);
       System.out.println("Please enter the amount of lowest numbers to drop."); 
       int n = input.nextInt();
       
       return n;
    }
  
   public static double calculateAverage(ArrayList<Double> numCopy, int n){
       double average;
       double sum = 0;
       
       Collections.sort(numCopy, Collections.reverseOrder()); //Sorting the array list in reverse.
       
       for(int counter = 0; counter < numCopy.size() - n; counter++){ 
           
                sum = sum + numCopy.get(counter);
        }
       
       average = sum / (numCopy.size() - n); //Finding the average of the array copy
       
       return average;
    }
  
   public static void printResults(ArrayList<Double> userNumbers, double average, int n){
       
      System.out.print("Given the numbers ");
                   
      for(int counter = 0; counter < userNumbers.size(); counter++){ //This should print out the original array.
          
           if(counter == userNumbers.size() - 1 ){ 
              System.out.print("and " + userNumbers.get(counter) + ", " );      
            }
           else{ 
              System.out.print(df2.format(userNumbers.get(counter)) + ", ");
            }
        }

      System.out.println("the average of all the numbers except the lowest " + n + " is " + df2.format(average) + ".");
         
    }
 
   public static void main(String args[]){
       
       ArrayList<Double> userNumbers = getArrayNumbers();
       int n = getLowestNumber();
       double average = calculateAverage(userNumbers, n);
       printResults(userNumbers, average, n);
       
    }
}

 

[alyafey22]

numCopy = new ArrayList<>(userNumbers)

This does not make a deep copy. The numCopy still references the original ArrayList. To make a deep copy add the elements to both arrays separately.

 

[smilesofmiles]

Okay, I added elements to the second array. Is there something I'm missing? The program still won't display the original numbers. Thank you for the response!

package calcavgdropsmallest;import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.Collections;

public class CalcAvgDropSmallest {
    
   private static DecimalFormat df2 = new DecimalFormat(".00");

   public static ArrayList<Double> getArrayNumbers(){
       Scanner input = new Scanner(System.in);
       
       System.out.println("Please enter five to ten numbers separated by spaces on one line.");
       
       ArrayList<Double> userNumbers = new ArrayList<>();
       ArrayList<Double> numCopy = new ArrayList<>(userNumbers); //Created a copy of the array.
       
       String numbers = input.nextLine();
       String[] strHolder = numbers.split("\\s+"); 
       
       for(int counter = 0; counter < strHolder.length; counter++){
           userNumbers.add(counter, Double.parseDouble(strHolder[counter])); //Adding numbers to the array
        } 
       for(int i = 0; i < strHolder.length; i++){
           numCopy.add(i, Double.parseDouble(strHolder[i])); //Adding numbers to the array copy
        }       
       
       return numCopy;
    }
   
   public static int getLowestNumber(){
       Scanner input = new Scanner(System.in);
       System.out.println("Please enter the amount of lowest numbers to drop."); 
       int n = input.nextInt();
       
       return n;
    }
  
   public static double calculateAverage(ArrayList<Double> numCopy, int n){
       double average;
       double sum = 0;
       
       Collections.sort(numCopy, Collections.reverseOrder()); //Sorting the array list in reverse.
       
       for(int counter = 0; counter < numCopy.size() - n; counter++){ 
           
                sum = sum + numCopy.get(counter);
        }
       
       average = sum / (numCopy.size() - n); //Finding the average of the array copy
       
       return average;
    }
  
   public static void printResults(ArrayList<Double> userNumbers, double average, int n){
       
      System.out.print("Given the numbers ");
                   
      for(int counter = 0; counter < userNumbers.size(); counter++){ //This should print out the original array.
          
           if(counter == userNumbers.size() - 1 ){ 
              System.out.print("and " + userNumbers.get(counter) + ", " );      
            }
           else{ 
              System.out.print(df2.format(userNumbers.get(counter)) + ", ");
            }
        }

      System.out.println("the average of all the numbers except the lowest " + n + " is " + df2.format(average) + ".");
         
    }
 
   public static void main(String args[]){
       
       ArrayList<Double> numbers = getArrayNumbers();
       int n = getLowestNumber();
       double average = calculateAverage(numbers, n);
       printResults(numbers, average, n);
       
    }
}

 

[I like Serena]

Hi smilesofmiles! ;)

You are creating two variables in getArrayNumbers()... and then you never use one of them nor pass it on.

Then you pass the original userNumbers to calculateAverage() giving it the different name numCopy within the function.
But that's not a copy - that is the original.
To fix it, we can use:

   public static double calculateAverage(final ArrayList<Double> userNumbers, int n){
       ArrayList<Double> numCopy = new ArrayList<Double>(userNumbers);
       ...
   }

That does make a proper copy of the list of Double's before changing it.
Note also the use of [m]final[/m] to ensure we don't accidentally try to change the original.

 

[smilesofmiles]

Thank you both! That last bit did the trick. :-) I think knowing how to do this will definitely help me with future projects. :D