BigData09 正则表达式及应用 compareTo源码分析和应用

1.正则表达式

/*
 * 邮箱验证
 * x_xx@scs.com.cn
 * abc@df.com
 * a|b a或者b
 * X?  X一次或一次也没有 
 * X*  X零次或多次 
 * X+  X一次或多次 
 * X{n,}  X至少 n 次 
 * ^ 行的开头  $ 行的结尾 
 */
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Demo{
    public static void main(String args[]) {
        String str = "sian_aax@qq.com.cn";
        String pattern = "^([a-z0-9A-Z]+[_|\\.]?)+[a-z0-9A-Z]@([a-z0-9A-Z]+(_[a-z0-9A-Z]+)?\\.)+[a-zA-Z]{2,}$";

        Pattern r = Pattern.compile(pattern);
        Matcher m = r.matcher(str);
        System.out.println(m.matches());
    }
}
    

/*
 * \b 单词边界 
 * \w 单词字符：[a-zA-Z_0-9] 
 * X{n} X，恰好 n 次 
 */
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class PatternDemo2 {
    public static void main(String[] args) {
        String s = "The Java language provides special support for the string "+
  "concatenation operator ( + ), and for conversion of"+
  "other objects to strings. String concatenation is implemented"+
  "through the {@code StringBuilder}(or {@code StringBuffer})";
 
        //获取所有两个字符的单词
        Pattern p = Pattern.compile("\\b\\w{3}\\b");
        //返回一个字符串的匹配器对象
        Matcher m = p.matcher(s);
        
/*        boolean b1 = m.find();
        if(b1){
            String str = m.group();
            System.out.println(str);
        }
        
        b1 = m.find();
        if(b1){
            String str = m.group();
            System.out.println(str);
        }

        b1 = m.find();
        if(b1){
            String str = m.group();
            System.out.println(str);
        }*/
        
        while(m.find()){
            System.out.println(m.group());
        }    
    }
}

/*
 * 切割功能使用正则表达式:
 */
public class RegexDemo4 {

    public static void main(String[] args) {
//        String s = "hello world  hi   hehe    mysql        oracle";
        //拆分字符串  一个以上空格都拆
//        String[] arr = s.split(" +");
        
        
//        String s = "hello.world.hi.hehe.mysql.oracle";
//        String[] arr = s.split("\\.");
        
        String s = "c:\\code\\day11\\test";
        //拆分字符串\\\\把\\拆出
        String[] arr = s.split("\\\\");
        
        
        for (int i = 0; i < arr.length; i++) {
            System.out.println(arr[i]);
        }
    }
}

/*
 * 正则表达式实现替换 ***
 */
public class RegexDemo5 {

    public static void main(String[] args) {
//        String s = "Hello world Hello world";
//        String replace = s.replace('l', 'L');
//        System.out.println(replace);
        
//        String replace = s.replace("world", "China");
//        System.out.println(replace);
//
//        String replace = s.replace("world", "China");
//        System.out.println(replace);
        
        //第一次索引遇到的l替换成A
//        String replaceFirst = s.replaceFirst("l", "A");
//        System.out.println(replaceFirst);
        
        //字符串中索引的l替换成A
//        String replaceAll = s.replaceAll("l", "A");
//        System.out.println(replaceAll);
        
        //要求:替换一个字符串中所有的"账号" --> "**"
        
        String s = "zhangsan账号123456789";
//        String replace = s.replace("账号", "**");
//        System.out.println(replace);
        //要求:替换一个字符串中所有的数字到*
//        String replaceAll = s.replaceAll("[0-9]+", "*");
//        System.out.println(replaceAll);
        //遇到数字就替换成*
        String replaceAll = s.replaceAll("[0-9]", "*");
        System.out.println(replaceAll);    
    }
}

2.compareTo源码分析

public class CompareDemo {

    public static void main(String[] args) {
        /*String s1 = "Hello";
        String s2 = "Hello";
        System.out.println(s1 == s2);
        System.out.println(s1.equals(s2));
        System.out.println(s1.compareTo(s2));//0
        */
        
        String ss1 = "ABCE";
        String ss2 = "ABCD";
        System.out.println(ss2.compareTo(ss1));//-1
        
        System.out.println("----------------");
        String s1 = "ABCDEFG";
        String s2 = "ABCDE";
        System.out.println(s1.compareTo(s2));//2
        
        
//        String res = s1.replace('l', 'L');
//        System.out.println(res);
    }

}