java复习笔记 string和stringbuilder

StringBuilder

练习题

 //输入一行字符 统计出数字字符的个数
        Scanner sc = new Scanner(System.in);
        char[] chars = sc.next().toCharArray();
        int index =0;
        for (int i = 0; i < chars.length; i++) {
            if (chars[i] >= '0' && chars[i] <= '9') {
                index++;
            }
        }
        System.out.println(index);

    }

代码实现

判断是不是回文数

        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        int left = 0, right = str.length() - 1;
        boolean hui = true;
        while (left < right) {
            if (str.charAt(left) != str.charAt(right)) hui = false;
            left++;
            right--;
        }

        System.out.println(hui ? "是回文" : "不是回文");

例题3：

这个思路 倒着循环 挨个判断 'a'^=32;可以让大写转成小写 小写转成大写