【Java学习笔记】正则表达式

1.简介：

正则表达式是Java 处理字符串、文本的重要工具。

java.util.regex.Pattern   匹配类：用模式匹配一个字符串所表达的抽象结果。

java.util.regex.Matcher   模式类：用来表示一个编译过的正则表达式。

2.例子

import java.util.regex.Pattern;

public class RegexDemo1 {
    public static void main(String arg[]) {
        String expr;
        String str;

        expr = "p.t";
        str = "pot";
        boolean b = Pattern.matches(expr,str);//静态方法，直接调用
        if(b)
            System.out.println(str + " matches pattern " + expr);
        else
            System.out.println(str + " does not match pattern " + expr);
    }
}

但是这个例子中的expr每次都要进行编译才能进行匹配，而下面的例子则不需要。

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

public class RegexDemo2 {
    public static void main(String arg[]) {
        String expr;
        String str;

        expr = "p//wt";//在Java语言中，//表示要插入正则表达式的反斜线，且后面的字符有特殊意义。/w 单词字符 
        str = "pot";
        Pattern pattern = Pattern.compile(expr);
        Matcher matcher = pattern.matcher(str);
        if(matcher.matches())
            System.out.println(str + " matches pattern " + expr);
        else
            System.out.println(str + " does not match pattern " + expr);
    }
}

以上这个例子中的pattern就可以重用了，比如：

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

public class RegexDemo3 {
    public static void main(String arg[]) {
        String expr;

        expr = "p[aeiou]t";
        Pattern pattern = Pattern.compile(expr);
        for(int i=0; i<arg.length; i++) {
            Matcher matcher = pattern.matcher(arg[i]);
            if(matcher.matches())
                System.out.println(arg[i] + " matches pattern " + expr);
            else
                System.out.println(arg[i] + " does not match pattern " + expr);
        }
    }
}

查找在一个段落中的匹配地：

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

public class RegexDemo4 {
    public static void main(String arg[]) {
        String expr;
        String str;

        expr = "bark";
        str = "This is a larger block of text the pattern matcher " +
              "will search for the word bark. The pattern is very " +
              "simple. It will only match the word bark, and nothing " +
              "else. You can search a block of text for any of the " +
              "regular expression patterns--not just bark.";
        Pattern pattern = Pattern.compile(expr);
        Matcher matcher = pattern.matcher(str);
        boolean found = matcher.find();
        while(found) {
            int location = matcher.start();
            System.out.println(expr + " found at " + location);
            found = matcher.find(location+1);
       }
    }
}
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综合例子：