Java基础 案例综合2

登录

public class Demo03 {
    public static void main(String[] args) {
        String username = "奥特曼";
        String password = "123456";
        for (int i = 1; i <= 3; i++) {
            Scanner sc = new Scanner(System.in);
            System.out.println("请输入账户");
            String name = sc.nextLine();
            System.out.println("请输入密码");
            String pwd = sc.nextLine();
            if (name.equals(username) && pwd.equals(password)) {
                System.out.println("登录成功");
                break;
            } else {
                if (2 - i == 0) {
                    System.out.println("你的账户被锁定");
                } else {
                    System.out.println("登录失败,你还有:" + (3 - i) + "次机会");
                }
            }
        }
    }
}

遍历字符串 

public class Demo04 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串：");
        String line = sc.nextLine();
        for (int i = 0; i <line.length(); i++){
            System.out.println(line.charAt(i));
        }
    }
}

 

 统计字符次数

public class Demo05 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串：");
        String line = sc.nextLine();
        int bigCount = 0;
        int smallCount = 0;
        int numberCount = 0;
        for (int i = 0; i < line.length(); i++) {
            char ch = line.charAt(i);
            if (ch > 'A' && ch < 'Z') {
                bigCount++;
            } else if (ch > 'a' && ch < 'z') {
                smallCount++;
            } else if (ch > '0' && ch < '9') {
                numberCount++;
            }
        }
        System.out.println("大写字母：" + bigCount + "个");
        System.out.println("小写字母：" + smallCount + "个");
        System.out.println("数字：" + numberCount + "个");
    }
}

 

字符串反转 

public class Demo06 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串：");
        String line = sc.nextLine();
        String s = reverse(line);
        System.out.println("s:" + s);
    }

    public static String reverse(String s) {
        String ss = "";
        for (int i = s.length() - 1; i >= 0; i--) {
            ss += s.charAt(i);
        }
        return ss;
    }
}

StringBuilder字符串拼接

public class Demo07 {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3};
        String s = arrayToString(arr);
        System.out.println("s:" + s);
    }

    public static String arrayToString(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]);
            } else {
                sb.append(arr[i]).append(",");
            }
        }
        sb.append("]");
        String s = sb.toString();
        return s;
    }
}

StringBuilder字符串反转

public class Demo08 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个字符串：");
        String line = sc.nextLine();
        String s = myReverse(line);
        System.out.println("s:" + s);
    }

    public static String myReverse(String s) {
        return new StringBuilder(s).reverse().toString();
    }
}