正则表达式：查找不匹配的点（或字符索引）

Question

我是正则表达式的初学者。当我们使用正则表达式验证字符串时，有什么方法可以找到不匹配的点或字符索引？我在 Java 中使用 RegEx 来验证字符串。
我只需要找到第一个不匹配的索引。
更新
请考虑这样的例子。
正则表达式：^\d{9}[VX]$
接受的字符串：547812375X
错误的字符串：547A12375X

在错误的字符串中，有 A 而不是 8。我需要找到不匹配的索引，因为这里是 4。索引处的字符与 RegEx 不匹配。

Answer 1

我认为这段代码可能会做你想做的事：

package so7783938;

import static org.junit.Assert.assertEquals;

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

import org.junit.Test;

public class RegexFailureTest {

  public static int firstFailurePoint(Pattern regex, String str) {
    for (int i = 0; i <= str.length(); i++) {
      Matcher m = regex.matcher(str.substring(0, i));
      if (!m.matches() && !m.hitEnd()) {
        return i - 1;
      }
    }
    if (regex.matcher(str).matches()) {
      return -1;
    } else {
      return str.length();
    }
  }

  @Test
  public void testSimple() {
    Pattern abc = Pattern.compile("abc");
    assertEquals(0, firstFailurePoint(abc, ""));
    assertEquals(1, firstFailurePoint(abc, "a"));
    assertEquals(2, firstFailurePoint(abc, "ab"));
    assertEquals(-1, firstFailurePoint(abc, "abc"));
    assertEquals(3, firstFailurePoint(abc, "abcd"));
    assertEquals(3, firstFailurePoint(abc, "abcdefghi"));
    assertEquals(1, firstFailurePoint(abc, "aaa"));
    assertEquals(2, firstFailurePoint(abc, "abb"));
  }

  @Test
  public void testAlternative() {
    Pattern regex = Pattern.compile("hello|world");
    assertEquals(0, firstFailurePoint(regex, "x"));
    assertEquals(-1, firstFailurePoint(regex, "hello"));
    assertEquals(-1, firstFailurePoint(regex, "world"));
    assertEquals(3, firstFailurePoint(regex, "hel"));
    assertEquals(5, firstFailurePoint(regex, "hello kitty"));
    assertEquals(3, firstFailurePoint(regex, "help me"));
    assertEquals(3, firstFailurePoint(regex, "worse is better"));
  }

  @Test
  public void testExample() {
    Pattern regex = Pattern.compile("^\\d{9}[VX]$");
    assertEquals(-1, firstFailurePoint(regex, "547812375X"));
    assertEquals(3, firstFailurePoint(regex, "547A12375X"));
  }

}