Improving expanding arrays, codehs 5.6.4

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Java

I feel a bit embarrassed to ask this because this is the first problem I have been actually stumped with over a long long amount of time... Here is the code:

public class ExpandingArray
{
    private static final int STARTING_SIZE = 10;
    private int[] arr;
    private int[] tempArr; 
    private int[] finalArr; 
    private int currentSize;
    private int numElements;
    
    public ExpandingArray()
    {
        arr = new int[STARTING_SIZE];
        currentSize = STARTING_SIZE;
        numElements = 0;
    }
    
    // Remove the element at index `index` and shift
    // all subsequent elements to the left. 
    public int remove(int index)
    {
        tempArr = new int[10]; 
        for(int i = 0; i < index; i++)
        {
            tempArr[i] = arr[i];
        }
        for(int i = index; i < arr.length - 1; i++)
        {
            tempArr[i] = arr[i + 1];
        }
        arr = new int[9];
        for(int i = 0; i < arr.length; i++)
        {
            arr[i] = tempArr[i];
        }
        return 0;
    }
    
    // Add the int `element` at the `index` in the array.
    // You'll need to shift everything one index to the right
    // after this index.
    public void add(int index, int element)
    {
        int [] tempArr = new int[arr.length + 1];
        for(int i = 0; i < index; i++)
        {
            tempArr[i] = arr[i];
        }
        tempArr[index] = element; 
        
        for(int k = index + 2; k <= tempArr.length; k++)
        {
            tempArr[k-1] = arr[k - 2];
        }
        
        int [] finalArr = new int[tempArr.length + 1];
        for(int i = 0; i < tempArr.length; i++)
        {
            finalArr[i] = tempArr[i];
        }
        finalArr[finalArr.length - 1] = arr[arr.length - 1];
        numElements = finalArr.length; 
        currentSize = finalArr.length; 
        arr = finalArr; 
 
    }
    
    // Return the number of elements in your array.
    public int size()
    {
        return arr.length;
    }
    
    private boolean isFull()
    {
        return numElements == currentSize;
    }
    
    private void expand()
    {
        System.out.println("Expanding");
        int newSize = currentSize * 2;
        int[] newArray = new int[newSize];
        
        // Copy over old elements
        for(int i = 0; i < currentSize; i++)
        {
            newArray[i] = arr[i];
        }
        
        currentSize = newSize;
        arr = newArray;
    }
    
    public int get(int index)
    {
        return arr[index];
    }
    
    public void add(int x)
    {
        if(isFull())
        {
            expand();
        }
        arr[numElements] = x;
        numElements++;
    }
    
    public String toString()
    {
        // Return empty curly braces if the array is empty
        if (numElements == 0)
        {
            return "{}";
        }
        
        // Return Elements 
        String str = "{";
        for (int i=0; i < numElements - 1; i++)
        {
            str += arr[i] + ", ";
        }
        if (str.length() > 0 && str.charAt(str.length()-2)==',')
        {
            str = str.substring(0, str.length()-2);
            str += "}";
        }
        return str;
    }
}

What I have tried:

The methods remove, add and size are the ones that are being submitted. I made remove and size work but for the life of me I cant make add work. Whenever I complied it, I would be missing the last term of the array. Whenever I modify the existing code and tried to change the values length, I would get an out of bounds exception or a random index would repeat itself 3 times! I tried creating a third array as well and increasing the index by one, but that resulted in errors that didn't exist before... I am incredibly frustrated, please help!