字符串indexOf(String substr，int fromIndex)方法 (String indexOf(String substr, int fromIndex) Method)

indexOf(String substr, int fromIndex) is a String method in Java and it is used to get the index of a specified substring in the string from given fromIndex. That means to search for the substring will start from the given index (fromIndex).

indexOf(String substr，int fromIndex)是Java中的String方法，用于從給定的fromIndex獲取字符串中指定子字符串的索引。 這意味著從指定索引( fromIndex )開始搜索子字符串。

If substring exists in the string from fromIndex, it returns the index of the first occurrence of the substring, if substring does not exist in the string, it returns -1.

如果從的fromIndex字符串中存在串，它返回字符串的第一個(gè)出現(xiàn)的位置，如果子字符串沒有字符串中存在，則返回-1。

Syntax:

句法：

int str_object.indexOf(String substr, int fromIndex);

Here,

這里，

• str_object is an object of main string in which we have to find the index of given substring.

  str_object是主字符串的對象，在其中我們必須找到給定子字符串的索引。

• substr is the part of the string to be found in the string.

  substr是要在字符串中找到的字符串的一部分。

• fromIndex is an index of the main string, from where method will start searching for the substring.

  fromIndex是主字符串的索引，方法將從該索引開始搜索子字符串。

It accepts a substring, from index and returns index of its first occurrence or -1 if substring does not exist in the string.

它從索引接受子字符串，并返回其第一次出現(xiàn)的索引；如果字符串中不存在子字符串，則返回-1。

Example:

例：

Input: String str = "IncludeHelp"Function call:str.indexOf("Help", 4)Output:7Input: String str = "IncludeHelp"Function call:str.indexOf("HELP, 2)Output:-1

Java code to demonstrate the example of String.indexOf() method

Java代碼演示String.indexOf()方法的示例

public class Main {public static void main(String[] args) {String str = "IncludeHelp";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.");} }

Output

輸出量

Help is found at 7 position. lude does not found. HELP does not found.

翻譯自: https://www.includehelp.com/java/string-indexOf-String-substr-int-fromindex-method-with-example.aspx

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