Java对正则表达式的支持

字符串

字符串中有对正则表达式的支持的方法：

1. matches(String regex)

   底层是调用了Pattern.matches(regex, this)方法

   Scanner sc = new Scanner(System.in);
   System.out.println("请输入字母");
   String str = sc.next();
   System.out.println(str.matches("(.*)a"));
   

2. replaceFirst(String regex, String replacement)

   底层是调用了Pattern.compile(regex).matcher(this).replaceFirst(replacement)方法

   Scanner sc = new Scanner(System.in);
   System.out.println("请输入字符串");
   String str = sc.next();
   String result = str.replaceFirst("a", "*");//把首个a替换为*
   System.out.println(result);
   

3. replaceAll(String regex, String replacement)

   底层是调用了Pattern.compile(regex).matcher(this).replaceAll(replacement)方法

   String regex = "你好";
   Scanner sc = new Scanner(System.in);
   System.out.println("请输入字符串");
   String str = sc.next();
   //String result = str.replaceAll(regex, "大家好");
   String result = str.replaceAll("\\d", "*");
   System.out.println(result);
   

4. replace(CharSequence target, CharSequence replacement)

   底层是调用了Pattern.compile(target.toString(), Pattern.LITERAL).matcher(this).replaceAll(Matcher.quoteReplacement(replacement.toString()))方法

   String regex = "h";
   Scanner sc = new Scanner(System.in);
   System.out.println("请输入字符串");
   String str = sc.next();
   //String con = str.replace("h", "*");//把字母h替换为*
   String con = str.replace("\\d", "*");
   System.out.println(con);
   

注意：replace中的参数是target，而不是regex，即replace和replaceAll相比，相同点都是能够替换全部指定的字符串。不同点是replace不支持正则，只能传字符串。

真正的正则类

Pattern p = Pattern.compile(String regex);

Matcher m = p.matcher(CharSequence input);

m.find()/m.lookingAt()/m.matches()/...

package top.lukeewin.demo23;

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

public class Demo02Pattern {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String input = sc.next();
        Pattern p = Pattern.compile("java");
        Matcher m = p.matcher(input);
        boolean matches = m.matches();//只有完全匹配才返回true
        boolean b1 = m.lookingAt();//只有以java开始的，才返回true
        boolean b2 = m.find();//任意位置有java，都返回true
        boolean b3 = m.find(3);//从指定索引3开始找，有java，则返回true
        System.out.println(matches);
        System.out.println(b1);
        System.out.println(b2);
        System.out.println(b3);
    }
}```