浅谈JAVA字符串匹配算法indexOf函数的实现方法

static String mainString = "Hello my name is HuangLinqing";
static String patternString = "HuangLinqing";
 
public static void main(String[] args) {
 System.out.printf(mainString.indexOf(patternString, 0) + "");
}

/**
 * Code shared by String and StringBuffer to do searches. The
 * source is the character array being searched, and the target
 * is the string being searched for.
 *
 * @param source the characters being searched.
 * @param sourceOffset offset of the source string.
 * @param sourceCount count of the source string.
 * @param target the characters being searched for.
 * @param targetOffset offset of the target string.
 * @param targetCount count of the target string.
 * @param fromIndex the index to begin searching from.
 */
static int indexOf(char[] source, int sourceOffset, int sourceCount,
 char[] target, int targetOffset, int targetCount,
 int fromIndex) {
 if (fromIndex >= sourceCount) {
 return (targetCount == 0 ? sourceCount : -1);
 }
 if (fromIndex < 0) {
 fromIndex = 0;
 }
 if (targetCount == 0) {
 return fromIndex;
 }
 char first = target[targetOffset];
 int max = sourceOffset + (sourceCount - targetCount);
 for (int i = sourceOffset + fromIndex; i <= max; i++) {
 /* Look for first character. */
 if (source[i] != first) {
  while (++i <= max && source[i] != first);
 }
 /* Found first character, now look at the rest of v2 */
 if (i <= max) {
  int j = i + 1;
  int end = j + targetCount - 1;
  for (int k = targetOffset + 1; j < end && source[j]
   == target[k]; j++, k++);
  if (j == end) {
  /* Found whole string. */
  return i - sourceOffset;
  }
 }
 }
 return -1;
}

if (fromIndex >= sourceCount) {
 return (targetCount == 0 ? sourceCount : -1);
}
if (fromIndex < 0) {
 fromIndex = 0;
}
if (targetCount == 0) {
 return fromIndex;
}

char first = target[targetOffset];
int max = sourceOffset + (sourceCount - targetCount);
 
for (int i = sourceOffset + fromIndex; i <= max; i++) {
 /* Look for first character. */
 if (source[i] != first) {
 while (++i <= max && source[i] != first);
 }
 /* Found first character, now look at the rest of v2 */
 if (i <= max) {
 int j = i + 1;
 int end = j + targetCount - 1;
 for (int k = targetOffset + 1; j < end && source[j]
  == target[k]; j++, k++);
 if (j == end) {
  /* Found whole string. */
  return i - sourceOffset;
 }
 }
}