Getting started with Java - using StringBuilder to print the contents of an array

StringBuilder overview:

• StringBuilder is a variable string class, we can regard it as an object container.
• Function: Improve the efficiency of string operations, such as splicing, modification, etc.

case:

• Design a method to output the content of any integer array, and the output format is required to be: [11,22,33,44]. 

public class StringBuilderDemo1 {
    public static void main(String[] args) {
        int[] arr1 = null;
        System.out.println(toString(arr1));

        int[] arr2 = {};
        System.out.println(toString(arr2));

        int[] arr3 = {11,22,33,44};
        System.out.println(toString(arr3));

    }

    /**
     * 1.定义方法接收任意整型数组，返回数组内容格式
     */
    public static String toString(int[] arr){
        if (arr != null){
            StringBuilder sb = new StringBuilder("[");
            for (int i = 0; i < arr.length; i++) {
                sb.append(arr[i]).append(i == arr.length - 1 ? "" : ",");
            }
            sb.append("]");
            return sb.toString();
        }else {
            return null;
        }
    }
}