判断数字

 题目：给一个不多于5位的正整数，要求：一、求它是几位数，二、逆序打印出各位数字。

数字倒序输出int-->string-->char[]-->string

    //方法一
    public static void getNum(){
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt();
        int count = 0;  //记录位数
        int weishu = 0;  //得到的每一位
        int nixu = 0;  //逆序数字
        if(num<0||num>99999){
            System.out.println("数值不符合要求");
            System.exit(0);
        }
        do {
            //这样倒叙太麻烦,采用第二种方式把int转为string,再由string转为char[],再由char[]变为string
            nixu = nixu*10;   //逆序数要*10来放下一位
            weishu = num % 10; //在num去掉末位数之前得到末位数
            nixu+=weishu;   //然后末位数加到逆序数上面
            
            num = num/10;
            count++;
            if (num==0) {
                break;
            }
        } while (true);
        System.out.println("一共有:"+count+"位,逆序为:"+nixu);        
    }

    //方法二
    public static void getNum2(){
        Scanner scanner = new Scanner(System.in);
        int num = scanner.nextInt();
        if (num<0||num>99999) {
            System.out.println("数值不符合要求");
            System.exit(0);
        }
        if(num >=0 && num <=9) {
            System.out.println( num + "是一位数");
            System.out.println("按逆序输出是" + '
' + num);
           } else if(num >= 10 && num <= 99) {
            System.out.println(num + "是二位数");
            System.out.println("按逆序输出是"+revert(num));
           } else if(num >= 100 && num <= 999) {
            System.out.println(num + "是三位数");
            System.out.println("按逆序输出是"+revert(num));
           } else if(num >= 1000 && num <= 9999) {
            System.out.println(num + "是四位数");
            System.out.println("按逆序输出是"+revert(num));
           } else if(num >= 10000 && num <= 99999) {
            System.out.println(num + "是五位数");
            System.out.println("按逆序输出是"+revert(num));
           }
    }
    //倒序输出
    public static String revert(int num){
        StringBuilder stringBuilder = new StringBuilder();    
        String result = Integer.toString(num);    //int转string
        char[] arr = result.toCharArray();    //string转char[]
        for (int i = arr.length-1; i >=0 ; i--) {
            stringBuilder.append(arr[i]);    //char[]转string
        }
        return stringBuilder.toString();
    }

源码