黑马程序员——javaSE_正则表达式

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正则表达式:符合一定规则的表达式

作用：用于专门操作字符串。可以简化对只付出的复杂操作。

特点：用于一些特定的符号来表示一些代码操作。简化书写。

弊端：符号定义越多，正则越长，阅读性越差。

import java.io.*;
public class Test {
	public static void main(String[] args) throws Exception{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String str = br.readLine();
		String reg = "[1-9]\d{4,14}";
		boolean b = str.matches(reg);
		if(b){
			System.out.println("正确");
		}else{
			System.out.println("错误");
		}
		
	}
}

例子:输入一个字符串，去除连续的字符，只保留1个

import java.io.*;
public class Test {
	public static void main(String[] args)throws Exception{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String str = br.readLine();
		String reg = "(.)\1+";
		String s = str.replaceAll(reg, "$1");
		System.out.println(s);
	}
}

例子:治疗口吃，我我我我....要要....学学学....编...编...程程..程 把这句话编程 我要学编程

public class Test {
	public static void main(String[] args){
		String str = "我我我我....要要....学学学....编...编...程程..程";
		String reg = "(\.)+";
		String reg2 = "(.)\1+";
		str = str.replaceAll(reg,"");
		str = str.replaceAll(reg2,"$1");
		System.out.println(str);
	}
}

例子:ming tian fang jia 获取4个字母组成的

import java.util.regex.*;
public class Test {
	public static void main(String[] args){
		String str = "ming tian fang jia";
		String reg = "(\b[a-z]{4}\b)+";
		Pattern p = Pattern.compile(reg);
		Matcher m = p.matcher(str);
		while(m.find()){
			System.out.println(m.group());
		}
	}
}

例子:获取外网IP和IP所属地

public class Test{
	public static void main(String[] args){
		BufferedReader br = null;
		ArrayList<String> s = new ArrayList<String>();
		try{
			URL u = new URL("http://www.ip.cn/");
			URLConnection url = u.openConnection();
			br = new BufferedReader(new InputStreamReader(url.getInputStream(),"UTF-8"));
			String str = null;
			String reg = "当前 IP：<code>[0-9\.]+</code>";
			String str2 = null;
			String str3 = null;
			String reg3 = "来自：.+</p><p>";
			while((str = br.readLine())!=null){
				Pattern p = Pattern.compile(reg);
				Matcher m = p.matcher(str);
				while(m.find()){
					str2 = m.group();
				}
				p = Pattern.compile(reg3);
				m = p.matcher(str);
				while(m.find()){
					str3 = m.group();
				}
			}
			String reg2 = "[0-9].+[0-9]";
			Pattern p = Pattern.compile(reg2);
			Matcher m = p.matcher(str2);
			while(m.find()){
				System.out.print("外网IP："+m.group());
			}
			reg3 = "[^</>p来自：]";
			p = Pattern.compile(reg3);
			m = p.matcher(str3);
			while(m.find()){
				s.add(m.group());
			}
			System.out.print("
地址:");
			for(String ss : s){
				System.out.print(ss);
			}
		}
		catch(IOException e){
			throw new RuntimeException("读入文件出错");
		}
	}
}