模式的子序列之后的量词确定模式的子序列如何重复的可能性。量词允许您指定要匹配的出现次数。
量词
X?：X，一次或不存在
X*：X，零次或多次
X+：X，一次或多次
X{n}：X，正好n次
X{n,}：X，至少n次
X{n,m}：X，至少n次，但不超过m次
package org.nhooo.example.regex;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class RegexQuantifierDemo {
public static void main(String[] args) {
String[] expressions =
{"x?", "x*", "x+", "x{2}", "x{2,}", "x{2,5}"};
String input = "xxxxxx yyyxxxxxx zzzxxxxxx";
for (String expression : expressions) {
// 将给定的正则表达式编译为
// 模式并创建一个匹配器
// 针对此模式的给定输入。
Pattern pattern = Pattern.compile(expression);
Matcher matcher = pattern.matcher(input);
// 查找每个匹配并打印
System.out.format("regex: %s %n", expression);
while (matcher.find()) {
System.out.format("Text \"%s\" found at %d to %d%n",
matcher.group(), matcher.start(),
matcher.end());
}
System.out.println("------------------------------");
}
}
}这是程序的结果：
regex: x?
Text "x" found at 0 to 1
Text "x" found at 1 to 2
Text "x" found at 2 to 3
Text "x" found at 3 to 4
Text "x" found at 4 to 5
Text "x" found at 5 to 6
Text "" found at 6 to 6
Text "" found at 7 to 7
Text "" found at 8 to 8
Text "" found at 9 to 9
Text "x" found at 10 to 11
Text "x" found at 11 to 12
Text "x" found at 12 to 13
Text "x" found at 13 to 14
Text "x" found at 14 to 15
Text "x" found at 15 to 16
Text "" found at 16 to 16
Text "" found at 17 to 17
Text "" found at 18 to 18
Text "" found at 19 to 19
Text "x" found at 20 to 21
Text "x" found at 21 to 22
Text "x" found at 22 to 23
Text "x" found at 23 to 24
Text "x" found at 24 to 25
Text "x" found at 25 to 26
Text "" found at 26 to 26
------------------------------
regex: x*
Text "xxxxxx" found at 0 to 6
Text "" found at 6 to 6
Text "" found at 7 to 7
Text "" found at 8 to 8
Text "" found at 9 to 9
Text "xxxxxx" found at 10 to 16
Text "" found at 16 to 16
Text "" found at 17 to 17
Text "" found at 18 to 18
Text "" found at 19 to 19
Text "xxxxxx" found at 20 to 26
Text "" found at 26 to 26
------------------------------
regex: x+
Text "xxxxxx" found at 0 to 6
Text "xxxxxx" found at 10 to 16
Text "xxxxxx" found at 20 to 26
------------------------------
regex: x{2}
Text "xx" found at 0 to 2
Text "xx" found at 2 to 4
Text "xx" found at 4 to 6
Text "xx" found at 10 to 12
Text "xx" found at 12 to 14
Text "xx" found at 14 to 16
Text "xx" found at 20 to 22
Text "xx" found at 22 to 24
Text "xx" found at 24 to 26
------------------------------
regex: x{2,}
Text "xxxxxx" found at 0 to 6
Text "xxxxxx" found at 10 to 16
Text "xxxxxx" found at 20 to 26
------------------------------
regex: x{2,5}
Text "xxxxx" found at 0 to 5
Text "xxxxx" found at 10 to 15
Text "xxxxx" found at 20 to 25
------------------------------