第14 章 ： 类库使用案例分析

59 StringBuffer使用

使用StringBuffer追加26个小写字母。逆序输出，并删除前5个字符
StringBuffer允许修改 String不允许修改

StringBuffer buff = new StringBuffer();
for(int i = 'a'; i<='z'; i++){
    buff.append((char)i);
}
System.out.println(buff.reverse().delete(0, 5));
// utsrqponmlkjihgfedcba

60 随机数组

Rondom 产生5个[1, 30]之间随机数

import java.util.Arrays;
import java.util.Random;

class NumberFactory{
    private static Random random = new Random();

    public static int[] getRandomList(int num){
        int[] list = new int[num];
        int foot = 0;

        while (foot < num) {
            int value = random.nextInt(31);
            if (value !=0 ){
                list[foot++] = value;
            }
        }
        return list;
    }
}

class Demo{
    public static void main(String[] args) {
        int[] list = NumberFactory.getRandomList(5);
        System.out.println(Arrays.toString(list));
        // [27, 3, 9, 4, 12]
    }
}

61 Email验证

class Validator{
    public static boolean isEmail(String email){
        if(email == null || "".equals(email)){
            return false;
        }

        String regex = "\\w+@\\w+\\.\\w+";
        return email.matches(regex);
    }
}

class Demo{
    public static void main(String[] args) {
        System.out.println(Validator.isEmail("ooxx@qq.com"));
        // true
    }
}

62 扔硬币

0-1随机数模拟投掷硬币 1000次

import java.util.Random;

class Coin{
    private int front;
    private int back;
    private Random random = new Random();

    public void throwCoin(int num){
        for (int i = 0; i < num; i++) {
            int value = random.nextInt(2);
            if (value == 0){
                this.front ++;
            } else{
                this.back ++;
            }
        }
    }

    public int getFront() {
        return this.front;
    }

    public int getBack() {
        return this.back;
    }
}

class Demo{
    public static void main(String[] args) {
        Coin coin = new Coin();
        coin.throwCoin(1000);

        System.out.println("正面： " + coin.getFront());
        System.out.println("背面： " + coin.getBack());
        // 正面： 495
        // 背面： 505
    }
}

63 IP验证

eg: 127.0.0.1
第一位 [12]?
第二位 [0-9]{0, 2}

import java.util.Random;

class Validator {
    public static boolean isIp(String ip) {
        String regex = "(\\d{1,3}\\.){3}\\d{1,3}";

        if (!ip.matches(regex)) {
            return false;
        }

        String[] list = ip.split("\\.");
        for (String str : list) {
            int num = Integer.parseInt(str);

            if (num > 255 || !str.equals(Integer.toString(num))) {
                return false;
            }
        }

        return true;
    }
}

class Demo {
    public static void main(String[] args) {
        System.out.println(Validator.isIp("127.0.0"));          // false
        System.out.println(Validator.isIp("127.0.0.1"));        // true
        System.out.println(Validator.isIp("255.255.255.255"));  // true
        System.out.println(Validator.isIp("255.255.255.666"));  // false
        System.out.println(Validator.isIp("255.255.001.1"));    // false
    }
}

64 HTML拆分

<font face="Arial,Serif" size="+2" color="red"></font>    

import java.util.regex.Matcher;
import java.util.regex.Pattern;

class Demo {
    public static void main(String[] args) {
        String html  = "<font face=\"Arial,Serif\" size=\"+2\" color=\"red\"></font>";
        String regex = "\\w+=\"[a-zA-Z0-9,\\+]+\"";
        Matcher matcher = Pattern.compile(regex).matcher(html);

        while (matcher.find()){
            String temp = matcher.group(0);
            String[] result = temp.split("=");
            System.out.println(result[0] + "\t" + result[1].replaceAll("\"", ""));
            /**
             * face   Arial,Serif
             * size   +2
             * color  red
             */
        }
    }
}

65 国家代码

实现国际化应用
输入国家代号，调用资源文件
3个资源文件

# message.properties
info=默认资源

# message_en_US.properties
info=英文资源

# message_zh_CN.properties
info=中文资源

import java.io.UnsupportedEncodingException;
import java.util.Locale;
import java.util.ResourceBundle;


class MessageUtil {
    // 将固定的内容定义为常量
    private static final String CHINA = "cn";
    private static final String ENGLISH = "en";
    private static final String BASENAME = "message";
    private static final String KEY = "info";

    public static String getMessage(String country) throws UnsupportedEncodingException {
        Locale locale = getLocale(country);

        if (locale == null) {
            return null;
        } else {
            ResourceBundle bundle = ResourceBundle.getBundle(BASENAME, locale);
            return new String(bundle.getString(KEY).getBytes("ISO-8859-1"), "utf-8");
        }
    }

    private static Locale getLocale(String country) {
        switch (country) {
            case CHINA:
                return new Locale("zh", "CN");
            case ENGLISH:
                return new Locale("en", "US");
            default:
                return null;
        }

    }


}

class Demo {
    public static void main(String[] args) throws UnsupportedEncodingException {
        if (args.length < 1) {
            System.out.println("请输入：cn 或者 en");
            System.exit(1);
        }
        System.out.println(MessageUtil.getMessage(args[0]));
        // 中文资源
    }
}

66 学生信息比较

先用成绩比较，如果相同按年龄比较
数据结构

姓名：年龄：成绩|姓名：年龄：成绩
eg:
张三:21:98|李四:23:96|王五:24:94

结构化的字符串处理

import java.io.UnsupportedEncodingException;
import java.util.Arrays;


class Student implements Comparable<Student>{
    private String name;
    private int age;
    private double score;

    public Student(String name, int age, double score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    @Override
    public int compareTo(Student other) {
        // 先用成绩比较，再用年龄比较
        if(this.score > other.score){
            return 1;
        } else if (this.score < other.score){
            return -1;
        } else{
            return this.age - other.age;
        }
    }

    @Override
    public String toString() {
        return "Student{" + name + ',' + age + ", " + score + "}";
    }
}

class Demo {
    public static void main(String[] args) throws UnsupportedEncodingException {
        String data = "张三:21:98|李四:23:96|王五:24:94";
        String[] list = data.split("\\|");
        Student[] students = new Student[list.length];

        for (int i = 0; i < list.length; i++) {
            String[] temp = list[i].split(":");
            students[i] = new Student(temp[0], Integer.parseInt(temp[1]), Double.parseDouble(temp[2]));
        }
        
        Arrays.sort(students);
        System.out.println(Arrays.toString(students));
        // [Student{王五,24, 94.0}, Student{李四,23, 96.0}, Student{张三,21, 98.0}]

    }
}