Java String indexOf（String substr）方法与示例
字符串indexOf（Stringsubstr）方法
indexOf（Stringsubstr）是Java中的String方法，用于获取字符串中指定子字符串的索引。
如果字符串中存在子字符串，则返回第一次出现的索引，如果字符串中不存在子字符串，则返回-1。
语法：
int str_object.indexOf(String substr);
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。
它接受子字符串并返回其首次出现的索引；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")
Output:
7
Input:
String str = "NHOOO"
Function call:
str.indexOf("HELP)
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);
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);
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);
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 is found at 3 position. HELP does not found.