StringBuffer,-Random,-正则简单使用

定义一个StringBuffer类对象, 然后向对象中添加26个小写的英文字母, 要求逆序的方式输出, 并且删除前5个字符.

public static void main(String[] args) {
        StringBuffer buf = new StringBuffer();
        for (int i = 'a'; i <= 'z'; i++) {
            buf.append((char)i);
        }
        buf.reverse();
        buf.delete(0, 5);
        System.out.println(buf);
}

利用Random类产生5个1~30之间(包含1和30)的随机数

class randomNumber {
    private static Random random = new Random();
    public static int [] create(int len) {
        int data [] = new int [len];
        int foot = 0;
        while(foot < data.length) {
            int num = random.nextInt(30);
            if (num != 0) {
                data[foot++] = num;
            }
        }
        return data;
    }
}
public class JavaAPIDemo {
    public static void main(String[] args) {
        int result [] = randomNumber.create(5);
        System.out.println(Arrays.toString(result));
    }
}

输入一个email地址, 使用正则表达式验证该Email地址是否正确

class Validator {
    public static boolean isEmail(String email) {
        if (email == null || email.equals("")) {
            return false;
        }
        String regex = "\\w+@\\w+\\.\\w+";
        return email.matches(regex);
    }
}
public class JavaAPIDemo {
    public static void main(String[] args) {
        String email = "w_ww@yund.com";
        System.out.println(Validator.isEmail(email));
    }
}

编写程序, 用0~1之间的随机数来模拟扔硬币实验, 统计扔1000次后出现的正面反面的次数并输出

class Coin {
    private int front; // 正面出现的次数
    private int back; // 反面出现的次护士
    private Random random = new Random();
    public void throwCoin(int num) {
        for (int i = 0; i < num; i++) {
            int temp = random.nextInt(2);
            if (temp == 0) {
                this.front++;
            } else {
                this.back++;
            }
        }
    }
    public int getFront() {
        return this.front;
    }
    public int getBack() {
        return this.back;
    }
}

public class JavaAPIDemo {
    public static void main(String[] args) {
        Coin coin = new Coin();
        coin.throwCoin(1000);
        System.out.println(coin.getBack());
        System.out.println(coin.getFront());
    }
}

编写正则表达式, 判断给定的是否是一个合法的ip ip第一位可能是1-2,可能没有, 且每一段不高于255

class Validator {
    public static boolean isIP(String ip) {
        if (ip == null || "".equals(ip)) {
            return false;
        }
        String regex = "([1-2]?[0-9]?[0-9]\\.){3}([1-2]?[0-9]?[0-9])";
        if (ip.matches(regex)) {
            String result[] = ip.split("\\.");
            for (int i = 0; i < result.length; i++) {
                int temp = Integer.parseInt(result[i]);
                if (temp > 255) {
                    return false;
                }
            }
        } else {
            return false;
        }
        return true;
    }
}
public class JavaAPIDemo {
    public static void main(String[] args) {
        String ip = "192.168.2.2";
        System.out.println(Validator.isIP(ip));
    }
}