Java: how to stop blank arrays position from showing null in the terminal?

Rodhis 0
Viewed 44

I have the following code that gets an element from the terminal with the Scanner class and adds it to a shopping cart array. It works fine, except that when I try to print the cart it'll show the unfilled positions of the array as "null". I digged over some topics here and someone sugested to create the first array with blank spaces for each of the 5 position (like String[] test = new String[]{"","","","",""};, but that didn't work. What should I do to "fix" this?

import java.util.Arrays;
import java.util.Scanner;

public class ex03 {
    public static void main(String[] args) {
        Scanner frutas = new Scanner(System.in);
        String[] nomesFrutas = new String[5];
        System.out.println("Insira a sua lista de compras.");

        for (int i = 0; i <= nomesFrutas.length; i++) {
            nomesFrutas[i] = frutas.next();
            System.out.println("As frutas no seu carrinho são: \r\n " + Arrays.toString(nomesFrutas));
            }
        }
    }
java arrays
1 Answers

it'll show the unfilled positions of the array as null

There's a couple ways to avoid uninitialized elements to show up.

A quick and lazy way would be to use the built-in functionality of the Arrays utility class. You can print a copy of the part that was populated and print it.

By the way, there's a bug in your code: condition i <= nomesFrutas.length would produce an ArrayIndexOutOfBounds during the very last iteration because nomesFrutas[i] would refer to an illegal index.

That's how you can make use of the utility method Arrays.copyOf():

for (int i = 0; i < nomesFrutas.length; i++) {
    nomesFrutas[i] = frutas.next();
    System.out.println("As frutas no seu carrinho são: \r\n "
         + Arrays.toString(Arrays.copyOf(nomesFrutas, i + 1)));
}

There are several drawbacks of this solution:

  • a new array needs to be allocated in memory at each iteration step just in order to print non-null elements (it's a good habit to be mindful while your action require creating new objects that are immediately thrown away, especially when it can be avoided);
  • as I've said it's a "lazy" way, because it doesn't require implementing things yourself, try not to overuse such ready-to-go options when you're learning.

Another approach would be to create your own method responsible for displaying a range of array elements:

for (int i = 0; i < nomesFrutas.length; i++) {
    nomesFrutas[i] = frutas.next();
    System.out.println("As frutas no seu carrinho são: \r\n ");
    display(nomesFrutas, i + 1);
}

public static void display(String[] arr, int len) {
    if (len < 1) return;
    
    System.out.print('[');
    for (int i = 0; i < len; i++) {
        System.out.print(arr[i]);
        if (i < len - 1) System.out.print(", ");
        else System.out.print(']');
    }
}

Fill free to play around with this solution and adjust it in whatever way you see fit.

Alexander Ivanchenko0
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