java String.indexof源码分析

public int indexOf(String str) {
return indexOf(str, 0);

}
public int indexOf(String str, int fromIndex) {
return indexOf(value, 0, value.length,
str.value, 0, str.value.length, fromIndex);
}

//source 字符串value sourceOffset 0 sourceCount 字符串length target 查询条件value

//targetOffset 0 targetCount 查询条件长度 fromIndex 下表

static int indexOf(char[] source, int sourceOffset, int sourceCount,
char[] target, int targetOffset, int targetCount,
int fromIndex) {

//如果查询下表大于等于字符串长度 

//如果查询条件长度==0就是""返回字符串长度等同于length()

//如果有查询条件返回-1
if (fromIndex >= sourceCount) {
return (targetCount == 0 ? sourceCount : -1);
}

//没有查询坐标就是0
if (fromIndex < 0) {
fromIndex = 0;
}

//如果没有查询条件返回下标
if (targetCount == 0) {
return fromIndex;
}
//字符数组 总是返回第一个
char first = target[targetOffset];

//int max = 0 +(总长度-查询条件的长度)
int max = sourceOffset + (sourceCount - targetCount);

for (int i = sourceOffset + fromIndex; i <= max; i++) {
/* Look for first character. */
if (source[i] != first) {//判断查询条件条件在不在source中以便循环
while (++i <= max && source[i] != first);
}
//循环
/* 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++);
//如果两个有相同的返回
if (j == end) {
/* Found whole string. */
return i - sourceOffset;//返回
}
}
}
return -1;//直接返回-1
}