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Java String Indexof

📅 2026-06-20 | 📂 Java
Java String indexOf() Method

Java String indexOf() Method

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Java String indexOf() Method

Java String Class Java String Class

The indexOf() method has the following four forms:

  • public int indexOf(int ch): Returns the index of the first occurrence of the specified character in this string, or -1 if the string does not contain such a character.
  • public int indexOf(int ch, int fromIndex): Returns the index of the first occurrence of the specified character in this string, starting the search at the specified index, or -1 if the string does not contain such a character.
  • int indexOf(String str): Returns the index of the first occurrence of the specified substring, or -1 if the string does not contain such a substring.
  • int indexOf(String str, int fromIndex): Returns the index of the first occurrence of the specified substring, starting the search at the specified index, or -1 if the string does not contain such a substring.

Syntax

public int indexOf(int ch ) or public int indexOf(int ch, int fromIndex) or int indexOf(String str) or int indexOf(String str, int fromIndex)

Parameters

  • ch -- a character, Unicode encoding.
  • fromIndex -- the index to start the search from. The first character is at index 0, the second at index 1, and so on.
  • str -- the substring to search for.

indexOf diagram

Return Value

The index of the first occurrence of the character or substring in the string, or -1 if not found.

Example 1

public class Main{
    public static void main(String args[]){
        String string = "aaa456ac";
        // Find the index of the specified character in the string. Returns the index if found; returns -1 if not found.
        System.out.println(string.indexOf("b")); // indexOf(String str); Returns: -1, "b" does not exist
        // Start searching from the fourth character position onwards, including the current position
        System.out.println(string.indexOf("a",3));//indexOf(String str, int fromIndex); Returns: 6
        // (Difference from above: the parameter above is of type String, the parameter below is of type int) Reference data: a-97, b-98, c-99
        // Search from the beginning to see if the specified character exists
        System.out.println(string.indexOf(99));//indexOf(int ch); Returns: 7
        System.out.println(string.indexOf('c'));//indexOf(int ch); Returns: 7
        // Search for ch from fromIndex. This is a character variable, not a string. The number corresponding to character 'a' is 97.
        System.out.println(string.indexOf(97,3));//indexOf(int ch, int fromIndex); Returns: 6
        System.out.println(string.indexOf('a',3));//indexOf(int ch, int fromIndex); Returns: 6
    }
}

The output is:

-1
6
7
7
6
6

Example 2

public class Test{
    public static void main(String args[]){
        String Str = new String(":www.");
        String SubStr1 = new String("");
        String SubStr2 = new String("com");
        System.out.print("Find the first occurrence of character 'o' :");
        System.out.println(Str.indexOf('o'));
        System.out.print("Find the first occurrence of character 'o' starting from position 14 :");
        System.out.println(Str.indexOf('o', 14));
        System.out.print("Find the first occurrence of substring SubStr1 :");
        System.out.println(Str.indexOf(SubStr1));
        System.out.print("Find the first occurrence of substring SubStr1 starting from position 15 :");
        System.out.println(Str.indexOf(SubStr1, 15));
        System.out.print("Find the first occurrence of substring SubStr2 :");
        System.out.println(Str.indexOf(SubStr2));
    }
}

The output of the above program is:

Find the first occurrence of character 'o' :12
Find the first occurrence of character 'o' starting from position 14 :17
Find the first occurrence of substring SubStr1 :9
Find the first occurrence of substring SubStr1 starting from position 15 :-1
Find the first occurrence of substring SubStr2 :16

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