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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 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

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

import java.util.regex.Matcher;import java.util.regex.Pattern;class Demo {
       public static void main(String[] args) {
           String html  = "";        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

# message.propertiesinfo=默认资源# message_en_US.propertiesinfo=英文资源# message_zh_CN.propertiesinfo=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

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
   
    {
       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}]    }}
   

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