Print an array in String without using Array.toString in Java

Question

I am trying to print a determined array in String form withoput using Arrays.toString function. What I have tried is the following but it turns out that method toString cannot be found and I don't know really what I am missing. I have hard times understanding the whole thinking process behind Java, so it would be great if you could explain me in detail what is happeing on each step. Thank a lot in advance!

class RandomIntArray { 
public static String toString(int[] a) {
       int[] array = {1, 2, 3, 4};
       System.out.print("[" + array[0]);
       for (int i = 1; i < array.length; i++) {
       System.out.print(", " + a[i]);
       System.out.println("]");
           }
    }
       public static void main (String[]args){
            System.out.println(toString[i]);
        }
    }

Answer 1

Problems

• toString[i] is not a method call (toString() is), brackets [] are for array access
• you misunderstand between arrays array and a
• you method toString must return a String but you return nothing, and print all inside the method itself

---

Solution

• the initial array must be defined in the main, and passed to the method
• the method toString must build a String and return it

public static String toString(int[] a) {
    StringBuilder sb = new StringBuilder("[" + a[0]);
    for (int i = 1; i < a.length; i++) {
        sb.append(", ").append(a[i]);
    }
    return sb.append("]").toString();
}

public static void main(String[] args) {
    int[] array = {1, 2, 3, 4};
    System.out.println(toString(array));
}

---

Improvement: handle empty array

It may be better to put all array access into the loop, because in case the array is empty, the previous code will fail at a[0]

public static String toString(int[] a) {
    String join = "";
    StringBuilder sb = new StringBuilder("[");
    for (int val : a) {
        sb.append(join).append(val);
        join = ", ";
    }
    return sb.append("]").toString();
}

Example

System.out.println(toString(new int[]{1, 2, 3, 4})); // [1, 2, 3, 4]
System.out.println(toString(new int[]{}));           // []