Java中的 Matcher start() 方法及示例

Matcher 类的start()方法用于获取已经完成的匹配结果的起始索引。

句法：

public int start()

参数：此方法不带任何参数。

返回值：该方法返回匹配的第一个字符的索引。0

异常：如果尚未尝试匹配，或者之前的匹配操作失败，则此方法抛出IllegalStateException 。

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*k)";
  
        // Create a pattern from regex
        Pattern pattern
            = Pattern.compile(regex);
  
        // Get the String to be matched
        String stringToBeMatched = "Geeks";
  
        // 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());
        }
    }
}

输出：

Current Matcher: java.util.regex.Matcher[pattern=(G*k) region=0,5 lastmatch=]
3

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 = "GFG";
  
        // 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());
        }
    }
}

输出：

Current Matcher: java.util.regex.Matcher[pattern=(G*G) region=0,3 lastmatch=]
0
2

参考： Oracle 文档