[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

 1 public class TestDemo {
 2     public static void main(String[] args) throws Exception{
 3         StringBuffer buffer = new StringBuffer();
 4         for(int x = 'a' ; x <= 'z' ; x++) {
 5             buffer.append((char)x);
 6         }
 7         System.out.println("[初始化数据]" + buffer);
 8         System.out.println("[逆序输出]" + buffer.reverse());
 9         System.out.println("[删除前五个字符]" + buffer.delete(0, 5));
10     }
11 }

• 面向对象实现（接口先行--子类实现--工厂解耦）

 1 interface IContent{
 2     public String content();
 3     public String reverse();
 4     public String delete(int index);
 5 }
 6 class StringContent implements IContent{
 7     private StringBuffer buffer = new StringBuffer();
 8     public StringContent() {
 9         for(int x = 'a' ; x <= 'z' ; x++) {
10             buffer.append((char)x);
11         }
12     }
13     @Override
14     public String content() {
15         return this.buffer.toString();
16     }
17     @Override
18     public String reverse() {
19         return this.buffer.reverse().toString();
20     }
21     @Override
22     public String delete(int index) {
23         return this.buffer.delete(0, index).toString();
24     }
25 }
26 class Factory{
27     private Factory() {}
28     public static IContent getInstance() {
29         return new StringContent();
30     }
31 }
32 public class TestDemo {
33     public static void main(String[] args) throws Exception{
34         IContent content = Factory.getInstance();
35         System.out.println("[初始化数据]" + content.content());
36         System.out.println("[逆序输出]" + content.reverse());
37         System.out.println("[删除前五个字符]" + content.delete(5));
38     }
39 }

• 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）

 1 package javaSE;
 2
 3 import java.util.Arrays;
 4 import java.util.Random;
 5
 6 interface INumber{
 7     public int[] getData();
 8 }
 9 class InvalidArrayLengthException extends RuntimeException{
10     public InvalidArrayLengthException() {}
11     public InvalidArrayLengthException(String str) {
12         super(str);
13     }
14 }
15 class RandomNumber implements INumber{
16     private int data[];
17     public RandomNumber() {
18         this(3);
19     }
20     public RandomNumber(int len) {
21         if(len <= 0) {
22             throw new InvalidArrayLengthException("数组长度不正确！");
23         }
24         this.data = new int[len];
25         this.createRandom();
26     }
27     public void createRandom() {
28         Random random = new Random();
29         for(int x = 0 ; x < this.data.length; x++) {
30             this.data[x] = random.nextInt(30) + 1;
31         }
32     }
33     @Override
34     public int[] getData() {
35         return this.data;
36     }
37 }
38 class Factory{
39     private Factory() {}
40     public static INumber getInstance(int ...args) {
41         if(args.length == 0) {
42             return new RandomNumber();
43         }else {
44             return new RandomNumber(args[0]);
45         }
46     }
47 }
48 public class TestDemo {
49     public static void main(String[] args) throws Exception{
50         INumber content = Factory.getInstance(5);
51         System.out.println(Arrays.toString(content.getData()));
52     }
53 }

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

 1 import java.util.Arrays;
 2 import java.util.Random;
 3
 4 interface IValidator{
 5     public boolean test() ;
 6 }
 7 class EmailValidator implements IValidator{
 8     public static final String DEFAULT_EMAIL_REGEX = "\\w+@\\w+\\.\\w+";
 9     private String regex;
10     private String content;
11     public EmailValidator(String content) {
12         this(content,DEFAULT_EMAIL_REGEX);
13         this.content = content;
14         this.regex = DEFAULT_EMAIL_REGEX;
15     }
16     public EmailValidator(String content,String regex) {
17         this.content = content;
18         this.regex = regex;
19     }
20     @Override
21     public boolean test() {
22         if(this.content == null || "".equals(this.content)) {
23             return false;
24         }
25         return this.content.matches(this.regex);
26     }
27 }
28 class Factory{
29     private Factory() {}
30     public static IValidator getInstance(String content,String ...regex) {
31         if(regex.length == 0) {
32             return new EmailValidator(content);
33         }else {
34             return new EmailValidator(content,regex[0]);
35         }
36     }
37 }
38 public class TestDemo {
39     public static void main(String[] args) throws Exception{
40         {IValidator validator = Factory.getInstance("muyan@yootk.com");
41         System.out.println(validator.test() ? "验证通过":"Email数据输入错误");}
42         {IValidator validator = Factory.getInstance("muyan@yootk.org",
43                 "[a-zA-Z][a-zA-Z0-9_\\-\\.]+@\\w+\\.(com|com\\.cn|net\\.cn|gov|edu|org)");
44         System.out.println(validator.test() ? "验证通过":"Email数据输入错误");}
45     }
46 }

• 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

 1 interface IValidator{
 2     public boolean test() ;
 3 }
 4 class IPHostValidator implements IValidator{
 5     public static final String DEFAULT_EMAIL_REGEX = "\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}";
 6     private String regex;
 7     private String content;
 8     public IPHostValidator(String content) {
 9         this(content, DEFAULT_EMAIL_REGEX);
10     }
11     public IPHostValidator(String content,String regex) {
12         this.content = content;
13         this.regex = regex;
14     }
15     @Override
16     public boolean test() {
17         if(this.content == null || "".equals(this.content)) {
18             return false;
19         }
20         if("0.0.0.0".equals(this.content)||"255.255.255.255".equals(this.content)) {
21             return false;
22         }
23         return this.content.matches(this.regex);
24     }
25 }
26 class Factory{
27     private Factory() {}
28     public static IValidator getInstance(String content,String ...regex) {
29         if(regex.length == 0) {
30             return new IPHostValidator(content);
31         }else {
32             return new IPHostValidator(content,regex[0]);
33         }
34     }
35 }
36 public class TestDemo {
37     public static void main(String[] args) throws Exception{
38         IValidator validator = Factory.getInstance("192.168.1.2");
39         System.out.println(validator.test() ? "验证通过":"IP数据输入错误");
40     }
41 }

• 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

 1 import java.util.regex.Matcher;
 2 import java.util.regex.Pattern;
 3
 4 interface IStringHandle{
 5     public String[] split();
 6 }
 7 class HTMLStringHandle implements IStringHandle{
 8     private String content;
 9     private String regex;
10     public HTMLStringHandle(String content,String regex) {
11         this.content = content;
12         this.regex = regex;
13     }
14     @Override
15     public String[] split() {
16         Matcher matcher = Pattern.compile(this.regex).matcher(this.content);
17         StringBuffer buffer = new StringBuffer(this.content.length());
18         while(matcher.find()) {
19             String value = matcher.group(0);
20             String temp[] = value.split("=");
21             buffer.append(temp[0]).append(":").append(temp[1].replaceAll("\"","")).append("|");
22         }
23         return buffer.toString().split("\\|");
24     }
25 }
26 class Factory{
27     private Factory() {}
28     public static IStringHandle getInstance(String content,String regex) {
29         return new HTMLStringHandle(content,regex);
30     }
31 }
32 public class TestDemo {
33     public static void main(String[] args) throws Exception{
34         String html = "<font face=\"Arial,Serif\" size=\"+2\" color=\"red\">";
35         String regex = "\\w+=\"[a-zA-Z0-9,\\+]+\"";
36         IStringHandle handle = Factory.getInstance(html, regex);
37         String result[] = handle.split();
38         for(String temp:result) {
39             System.out.println(temp);
40         }
41     }
42 }

• 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

 1 import java.util.Locale;
 2 import java.util.ResourceBundle;
 3
 4 interface IMessage{
 5     public String get(String key);
 6 }
 7
 8 class ResourceMessage implements IMessage{
 9     private static final String BASE_NAME = "Message";
10     private ResourceBundle resourceBundle;
11     public ResourceMessage(Locale locale){
12         this.resourceBundle = ResourceBundle.getBundle(BASE_NAME,locale);
13     }
14
15     @Override
16     public String get(String key){
17         try{
18             return this.resourceBundle.getString(key);
19         }catch (Exception e){
20             return null;
21         }
22     }
23 }
24
25 class ParameterException extends RuntimeException{
26     public ParameterException(){}
27     public ParameterException(String msg){
28         super(msg);
29     }
30 }
31
32 class Factory{
33     private Factory(){}
34     public static IMessage getInstance(String args[]){
35         if(args.length != 1 || !args[0].matches("\\d")){
36             throw new ParameterException("初始参数配置错误，无法执行");
37         }
38         int select = Integer.parseInt(args[0]);
39         switch (select){
40             case 1:
41                 return new ResourceMessage(Locale.CHINESE);
42             case 2:
43                 return new ResourceMessage(Locale.US);
44             default:
45                 return null;
46         }
47     }
48 }
49
50 public class YootkDemo {
51     public static void main(String[] args) throws Exception{
52         IMessage message = Factory.getInstance(args);
53         System.out.println(message.get("welcome.info"));
54     }
55 }

>> Hello

参考

idea：Maven项目，pom.xml中的resources标签

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