练习

一：String反转

public class Test1 {
    public static void main(String[] args) {
        String string = "abcdef";
        try {
            System.out.println(reverse(string, -1, 4));
        } catch (Exception e) {
            System.out.println(e.getMessage());;
        }
    }
    public static String reverse(String str, int start, int end) {
        //还可以添加验证
        //1: 先想出正确的
        //2: 然后再取反（因为正确的容易想到）
        if (!(str != null && start > end && start < str.length() &&
              end < str.length() && start != end && start > +0)) {
            throw new RuntimeException("参数不正确");
        }
        //先将String转换为char类型数组
        char[] chars = str.toCharArray();
        for (int i = start, j = end; i < j; i++, j--) {
            char temp = chars[i];
            chars[i] = chars[j];
            chars[j] = temp;
        }
        return new String(chars);
    }
}

二：注册处理

三：字符串统计

public class Test3 {
    public static void main(String[] args) {
        String name = "Han shun Ping";
        System.out.println(printName(name));
    }
    public static String printName(String str) {
        String[] s = str.split(" ");
        String resultString = String.format("%s,%s .%c" ,s[2],s[0],s[0].toUpperCase().charAt(0));
        return resultString;
    }
}

四：统计字符串

public class Test4 {
    public static void main(String[] args) {
        String str = "saddfHOHN  1q534215";
        countSting(str);
    }
    public static void countSting(String str){
        int NumCount = 0;
        int LowerCount = 0;
        int UpCount = 0;
        int Other = 0;
        for (int i = 0; i < str.length(); i++) {
            if(str.charAt(i)>='A'  && str.charAt(i)<= 'Z'){
                UpCount++;
            }else if (str.charAt(i)>='0'  && str.charAt(i)<= '9'){
                NumCount++;
            }else if (str.charAt(i)>='a'  && str.charAt(i)<= 'z'){
                LowerCount++;
            }else {
                Other++;
            };
        }
        System.out.println("数字有："+ NumCount);
        System.out.println("大写字母有："+ UpCount);
        System.out.println("小写字母有："+ LowerCount);
        System.out.println("其他有："+ Other);
    }
}

五：