Java中的 Matcher start(int) 方法和示例

Matcher 类的start(int group)方法用于从指定的组中获取已经完成的匹配结果的开始索引。

句法：

public int start(int group)

参数：此方法采用参数组，该组是需要匹配模式的起始索引的组。

返回值：此方法返回从指定组匹配的第一个字符的索引。

异常：此方法抛出：

• 如果尚未尝试匹配，或者之前的匹配操作失败，则IllegalStateException 。
• IndexOutOfBoundsException如果模式中没有具有给定索引的捕获组。

下面的示例说明了 Matcher.start() 方法：

示例 1：

// Java code to illustrate start() method
  
import java.util.regex.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // Get the regex to be checked
        String regex = "(G*s)";
  
        // Create a pattern from regex
        Pattern pattern
            = Pattern.compile(regex);
  
        // Get the String to be matched
        String stringToBeMatched
            = "GeeksForGeeks";
  
        // Create a matcher for the input String
        Matcher matcher
            = pattern
                  .matcher(stringToBeMatched);
  
        // Get the current matcher state
        MatchResult result
            = matcher.toMatchResult();
        System.out.println("Current Matcher: "
                           + result);
  
        while (matcher.find()) {
            // Get the first index of match result
            System.out.println(matcher.start(1));
        }
    }
}

输出：

Current Matcher: java.util.regex.Matcher[pattern=(G*s) region=0,13 lastmatch=]
4
12

示例 2：

// Java code to illustrate start() method
  
import java.util.regex.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // Get the regex to be checked
        String regex = "(G*G)";
  
        // Create a pattern from regex
        Pattern pattern
            = Pattern.compile(regex);
  
        // Get the String to be matched
        String stringToBeMatched
            = "GFGFGFGFGFGFGFGFGFG";
  
        // Create a matcher for the input String
        Matcher matcher
            = pattern
                  .matcher(stringToBeMatched);
  
        // Get the current matcher state
        MatchResult result
            = matcher.toMatchResult();
        System.out.println("Current Matcher: "
                           + result);
  
        while (matcher.find()) {
            // Get the first index of match result
            System.out.println(matcher.start(0));
        }
    }
}

输出：

Current Matcher: java.util.regex.Matcher[pattern=(G*G) region=0,19 lastmatch=]
0
2
4
6
8
10
12
14
16
18

参考： Oracle 文档