Java String indexOf（String substr，int fromIndex）方法，带示例
字符串indexOf（Stringsubstr，intfromIndex）方法
indexOf（Stringsubstr，intfromIndex）是Java中的String方法，用于从给定的fromIndex获取字符串中指定子字符串的索引。这意味着搜索子字符串将从给定索引(fromIndex)开始。
如果fromfrom的字符串中存在子字符串，则返回该子字符串首次出现的索引，如果该字符串中不存在子字符串，则返回-1。
语法：
int str_object.indexOf(String substr, int fromIndex);
这里，
str_object是主字符串的对象，我们必须在其中找到给定子字符串的索引。
substr是字符串中要在字符串中找到的部分。
fromIndex是主字符串的索引，方法将从该索引开始搜索子字符串。
它从索引接受子字符串，并返回其第一次出现的索引；如果字符串中不存在子字符串，则返回-1。
示例
Input:
String str = "NHOOO"
Function call:
str.indexOf("Help", 4)
Output:
7
Input:
String str = "NHOOO"
Function call:
str.indexOf("HELP, 2)
Output:
-1Java代码演示String.indexOf()方法的示例
public class Main
{
public static void main(String[] args) {
String str = "NHOOO";
String substr = "";
int index;
substr = "Help";
index = str.indexOf(substr, 4);
if(index != -1)
System.out.println(substr + " is found at " + index + " position.");
else
System.out.println(substr + " does not found.");
substr = "lude";
index = str.indexOf(substr, 8);
if(index != -1)
System.out.println(substr + " is found at " + index + " position.");
else
System.out.println(substr + " does not found.");
substr = "HELP";
index = str.indexOf(substr, 2);
if(index != -1)
System.out.println(substr + " is found at " + index + " position.");
else
System.out.println(substr + " does not found.");
}
}输出结果
Help is found at 7 position. lude does not found. HELP does not found.