Arrays.toString的编写

 public static String arrtostring1(int []arr){
        String s="[";
        if(arr==null) return "";
        if(arr.length==0) return "[]";  //数组长度可能为0，例如int []a=new int [0];
        for (int i = 0; i < arr.length; i++) {
            if(i!=arr.length-1)
            s=s+arr[i]+", ";
            else s=s+arr[i];
        }
        s=s+"]";
        return s;
    }

public static String arrtostring2(int []arr){
        StringBuilder sb=new StringBuilder();
        sb.append("[");
        for (int i = 0; i < arr.length; i++) {
            if(i!=arr.length-1){
                sb.append(arr[i]).append(", ");
            }
            else sb.append(arr[i]);
        }
        sb.append("]");
        return sb.toString();
    }

public static String arrtostring3(int []arr){
        StringJoiner sj=new StringJoiner(", ","[","]");
        for (int i = 0; i < arr.length; i++) {
            sj.add(arr[i]+"");
        }
        String s=sj.toString();
        return s;
    }