[Java] 类库例题

例1 字符串操作

定义一个StringBuffer类对象，然后通过append()方法向对象中添加26个小写字母，每次只添加一次，共添加26次，然后按逆序方式输出，并且可以删除前5个字符

• 面向过程实现

public class TestDemo {
    public static void main(String[] args) throws Exception{
        StringBuffer buffer = new StringBuffer();
        for(int x = 'a' ; x <= 'z' ; x++) {
            buffer.append((char)x);
        }
        System.out.println("[初始化数据]" + buffer);
        System.out.println("[逆序输出]" + buffer.reverse());
        System.out.println("[删除前五个字符]" + buffer.delete(0, 5));
    }
}

• 面向对象实现（接口先行--子类实现--工厂解耦）

interface IContent{
    public String content();
    public String reverse();
    public String delete(int index);
}
class StringContent implements IContent{
    private StringBuffer buffer = new StringBuffer();
    public StringContent() {
        for(int x = 'a' ; x <= 'z' ; x++) {
            buffer.append((char)x);
        }
    }
    @Override
    public String content() {
        return this.buffer.toString();
    }
    @Override
    public String reverse() {
        return this.buffer.reverse().toString();
    }
    @Override
    public String delete(int index) {
        return this.buffer.delete(0, index).toString();
    }
}
class Factory{
    private Factory() {}
    public static IContent getInstance() {
        return new StringContent();
    }
}
public class TestDemo {
    public static void main(String[] args) throws Exception{
        IContent content = Factory.getInstance();
        System.out.println("[初始化数据]" + content.content());
        System.out.println("[逆序输出]" + content.reverse());
        System.out.println("[删除前五个字符]" + content.delete(5));
    }
}

• 先定义出公共处理标准，随后依据此标准进行项目的具体实现
• 对于接口子类的获取采用工厂模式 

例2 生成随机数

利用Random类产生5个1~30之间（包括1和30）的随机整数

• 接口：描述最终目的
• 异常类：继承RuntimeException，业务异常，不希望此异常直接出现在方法的定义声明处（如果继承Exception会强制处理）

package javaSE;

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

interface INumber{
    public int[] getData();
}
class InvalidArrayLengthException extends RuntimeException{
    public InvalidArrayLengthException() {}
    public InvalidArrayLengthException(String str) {
        super(str);
    }
}
class RandomNumber implements INumber{
    private int data[];
    public RandomNumber() {
        this(3);
    }
    public RandomNumber(int len) {
        if(len <= 0) {
            throw new InvalidArrayLengthException("数组长度不正确！");
        }
        this.data = new int[len];
        this.createRandom();
    }
    public void createRandom() {
        Random random = new Random();
        for(int x = 0 ; x < this.data.length; x++) {
            this.data[x] = random.nextInt(30) + 1;
        }
    }
    @Override
    public int[] getData() {
        return this.data;
    }
}
class Factory{
    private Factory() {}
    public static INumber getInstance(int ...args) {
        if(args.length == 0) {
            return new RandomNumber();
        }else {
            return new RandomNumber(args[0]);
        }
    }
}
public class TestDemo {
    public static void main(String[] args) throws Exception{
        INumber content = Factory.getInstance(5);
        System.out.println(Arrays.toString(content.getData()));
    }
}

例3 Email验证

输入一个Email地址，用正则表达式验证该Email是否正确

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

interface IValidator{
    public boolean test() ;
}
class EmailValidator implements IValidator{
    public static final String DEFAULT_EMAIL_REGEX = "\w+@\w+\.\w+";
    private String regex;
    private String content;
    public EmailValidator(String content) {
        this(content,DEFAULT_EMAIL_REGEX);
        this.content = content;
        this.regex = DEFAULT_EMAIL_REGEX;
    }
    public EmailValidator(String content,String regex) {
        this.content = content;
        this.regex = regex;
    }
    @Override
    public boolean test() {
        if(this.content == null || "".equals(this.content)) {
            return false;
        }
        return this.content.matches(this.regex);
    }
}
class Factory{
    private Factory() {}
    public static IValidator getInstance(String content,String ...regex) {
        if(regex.length == 0) {
            return new EmailValidator(content);
        }else {
            return new EmailValidator(content,regex[0]);
        }
    }
}
public class TestDemo {
    public static void main(String[] args) throws Exception{
        {IValidator validator = Factory.getInstance("muyan@yootk.com");
        System.out.println(validator.test() ? "验证通过":"Email数据输入错误");}
        {IValidator validator = Factory.getInstance("muyan@yootk.org",
                "[a-zA-Z][a-zA-Z0-9_\-\.]+@\w+\.(com|com\.cn|net\.cn|gov|edu|org)");
        System.out.println(validator.test() ? "验证通过":"Email数据输入错误");}
    }
}

• 即可使用默认的正则表达式，也可根据需要扩充

例4 IP地址验证

编写正则表达式，判断给定的IP地址是否合法 

interface IValidator{
    public boolean test() ;
}
class IPHostValidator implements IValidator{
    public static final String DEFAULT_EMAIL_REGEX = "\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}";
    private String regex;
    private String content;
    public IPHostValidator(String content) {
        this(content, DEFAULT_EMAIL_REGEX);
    }
    public IPHostValidator(String content,String regex) {
        this.content = content;
        this.regex = regex;
    }
    @Override
    public boolean test() {
        if(this.content == null || "".equals(this.content)) {
            return false;
        }
        if("0.0.0.0".equals(this.content)||"255.255.255.255".equals(this.content)) {
            return false;
        }
        return this.content.matches(this.regex);
    }
}
class Factory{
    private Factory() {}
    public static IValidator getInstance(String content,String ...regex) {
        if(regex.length == 0) {
            return new IPHostValidator(content);
        }else {
            return new IPHostValidator(content,regex[0]);
        }
    }
}
public class TestDemo {
    public static void main(String[] args) throws Exception{
        IValidator validator = Factory.getInstance("192.168.1.2");
        System.out.println(validator.test() ? "验证通过":"IP数据输入错误");
    }
}

• 实际开发中除了核心代码，最常见的就是数据验证功能

例5 HTML拆分

给定一段HTML代码：“<font face="Arial,Serif" size="+2" color="red">”，拆分为

face=Arial,Serif

size=+2

color=red

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

interface IStringHandle{
    public String[] split();
}
class HTMLStringHandle implements IStringHandle{
    private String content;
    private String regex;
    public HTMLStringHandle(String content,String regex) {
        this.content = content;
        this.regex = regex;
    }
    @Override
    public String[] split() {
        Matcher matcher = Pattern.compile(this.regex).matcher(this.content);
        StringBuffer buffer = new StringBuffer(this.content.length());
        while(matcher.find()) {
            String value = matcher.group(0);
            String temp[] = value.split("=");
            buffer.append(temp[0]).append(":").append(temp[1].replaceAll(""","")).append("|");
        }
        return buffer.toString().split("\|");
    }
}
class Factory{
    private Factory() {}
    public static IStringHandle getInstance(String content,String regex) {
        return new HTMLStringHandle(content,regex);
    }
}
public class TestDemo {
    public static void main(String[] args) throws Exception{
        String html = "<font face="Arial,Serif" size="+2" color="red">";
        String regex = "\w+="[a-zA-Z0-9,\+]+"";
        IStringHandle handle = Factory.getInstance(html, regex);
        String result[] = handle.split();
        for(String temp:result) {
            System.out.println(temp);
        }
    }
}

• 可使用HTMLParser+XPath 

例6 国际化应用

从命令行输入国家代号，1代表中国，2代表美国，然后根据不同代号调用不同的资源文件显示信息

• 编写资源文件 
• 加载资源文件
• 通过IMessage接口，根据key获取数据

import java.util.Locale;
import java.util.ResourceBundle;

interface IMessage{
    public String get(String key);
}

class ResourceMessage implements IMessage{
    private static final String BASE_NAME = "Message";
    private ResourceBundle resourceBundle;
    public ResourceMessage(Locale locale){
        this.resourceBundle = ResourceBundle.getBundle(BASE_NAME,locale);
    }

    @Override
    public String get(String key){
        try{
            return this.resourceBundle.getString(key);
        }catch (Exception e){
            return null;
        }
    }
}

class ParameterException extends RuntimeException{
    public ParameterException(){}
    public ParameterException(String msg){
        super(msg);
    }
}

class Factory{
    private Factory(){}
    public static IMessage getInstance(String args[]){
        if(args.length != 1 || !args[0].matches("\d")){
            throw new ParameterException("初始参数配置错误，无法执行");
        }
        int select = Integer.parseInt(args[0]);
        switch (select){
            case 1:
                return new ResourceMessage(Locale.CHINESE);
            case 2:
                return new ResourceMessage(Locale.US);
            default:
                return null;
        }
    }
}

public class YootkDemo {
    public static void main(String[] args) throws Exception{
        IMessage message = Factory.getInstance(args);
        System.out.println(message.get("welcome.info"));
    }
}

>> Hello 

参考

idea：Maven项目，pom.xml中的resources标签

https://blog.csdn.net/qq_36134376/article/details/90762263