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Thread: My copied array is empty, and I don't know why.

  1. #1
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    Default My copied array is empty, and I don't know why.

    Doing some array experimenting, I attempted to to copy each element matching the value a user is looking for from the "arr" array to the "valuesFound" array Here's my code:

    SamsArrays.java
    package samsExperiments;
    import java.util.Arrays;
    import java.util.Scanner;
     
    public class SamsArrays {	
     
    	public int[] findAndStoreValues(int[]arr, int[]valuesFound) {
    		System.out.println("What integer value are you looking for:");
    		Scanner input = new Scanner(System.in);
    		int value = input.nextInt();
    		int j = 0;
    		for(int i = 0; i < arr.length; i++) {
    			if(i == value) {
    				System.out.println("Found a " + value + ". Copying it to the valuesFound array.");
    				arr[i] = valuesFound[j];
    				j++;
    			}
    		}
    		if(valuesFound == null) {
    			System.out.println("No " + value + " values were found to copy. valuesFound array is empty.");
    		}
    		return valuesFound;
    	}	
    }

    SamsExperimentsMain.java
    package samsExperiments;
     
    import java.util.Scanner;
    import java.util.Arrays;
    import SortingAlgorithms.*;
    import customExceptions.BuiltInExceptions;
     
    public class SamsExperimentsMain {
     
    	public static void main(String[] args){
     
    		SamsArrays x = new SamsArrays();
    		int[] arr = {17,41,3,5,22,54,6,29,3,13};		
    		System.out.println("We start out with: " + Arrays.toString(arr));
     
    		int[] valuesFound = new int[10];
    		valuesFound = x.findAndStoreValues(arr, valuesFound);
    		System.out.println("Our valuesFound array now has: " + Arrays.toString(valuesFound));		
     
    	}//end of main method	
     
    }//end of class

    The output looks like this:


    We start out with: [17, 41, 3, 5, 22, 54, 6, 29, 3, 13]
    What integer value are you looking for:
    3
    Found a 3. Copying it to the valuesFound array.
    Our valuesFound array now has: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]


    As you can see, the arr array we started out with has two 3's in it, but it doesn't even seem to go through the whole arr array, because we should be seeing, "Found a 3. Copying it to the valuesFound array" printed out twice, not once. What's more, the valuesFound array should have become "[3, 3, 0, 0, 0, 0, 0, 0, 0, 0]". What happened?

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: My copied array is empty, and I don't know why.

    valuesFound array now has: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
    Where does the code change any values in the valuesFound array?

       if(i == value) {   // compares value of array index to user's input
    What is the purpose of comparing user's input against the array's index value. Shouldn't the code be looking at the values in the arr array?
       if(arr[i] == value) {   // compare value in array with user's input
    If you don't understand my answer, don't ignore it, ask a question.

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