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Java String indexOf()

  • Difficulty Level : Medium
  • Last Updated : 07 Sep, 2021

There are four variants of indexOf() method. This article depicts about all of them, as follows: 
1.int indexOf() : This method returns the index within this string of the first occurrence of the specified character or -1, if the character does not occur.
 

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Syntax:
int indexOf(char ch )
Parameters:
ch : a character.

Java




// Java code to demonstrate the working
// of String indexOf()
public class Index1 {
public static void main(String args[])
    {
 
        // Initialising String
        String gfg = new String("Welcome to geeksforgeeks");
 
        System.out.print("Found g first at position : ");
 
        // Initial index of 'g' will print
        // prints 11
        System.out.println(gfg.indexOf('g'));
    }
}
Output
Found g first at position : 11

2. int indexOf(char ch, int strt ) : This method returns the index within this string of the first occurrence of the specified character, starting the search at the specified index or -1, if the character does not occur.
 

Syntax:
int indexOf(char ch, int strt)
Parameters:
ch :a character.
strt : the index to start the search from.

Java




// Java code to demonstrate the working
// of String indexOf(char ch, int strt)
public class Index2 {
public static void main(String args[])
    {
 
        // Initialising String
        String gfg = new String("Welcome to geeksforgeeks");
 
        System.out.print("Found g after 13th index at position : ");
 
        // 2nd index of 'g' will print
        // prints 19
        System.out.println(gfg.indexOf('g', 13));
    }
}
Output



Found g after 13th index at position : 19

3.int indexOf(String str) : This method returns the index within this string of the first occurrence of the specified substring. If it does not occur as a substring, -1 is returned.
 

Syntax:
int indexOf(String str)
Parameters:
str : a string.

Java




// Java code to demonstrate the working
// of String indexOf(String str)
public class Index3 {
public static void main(String args[])
    {
 
        // Initialising string
        String Str = new String("Welcome to geeksforgeeks");
 
        // Initialising search string
        String subst = new String("geeks");
 
        // print the index of initial character
        // of Substring
        // prints 11
        System.out.print("Found geeks starting at position : ");
        System.out.print(Str.indexOf(subst));
    }
}
Output
Found geeks starting at position : 11

4. int indexOf(String str, int strt) : This method returns the index within this string of the first occurrence of the specified substring, starting at the specified index. If it does not occur, -1 is returned. 
 

Syntax:
int indexOf(String str, int strt)
Parameters:
strt: the index to start the search from.
str : a string.
 

Java




// Java code to demonstrate the working
// of String indexOf(String str, int strt)
public class Index4 {
public static void main(String args[])
    {
 
        // Initialising string
        String Str = new String("Welcome to geeksforgeeks");
 
        // Initialising search string
        String subst = new String("geeks");
 
        // print the index of initial character
        // of Substring after 14th position
        // prints 19
        System.out.print("Found geeks(after 14th index) starting at position : ");
        System.out.print(Str.indexOf(subst, 14));
    }
}
Output
Found geeks(after 14th index) starting at position : 19

Some related applications:
 

  • Finding out if a given character (maybe anything upper or lower case) is a vowel or consonant. 
    Implementation is given below: 
     

JAVA




class Vowels
{
        // function to check if the passed 
        // character is a vowel
    public static boolean vowel(char c)
    {
        return "aeiouAEIOU".indexOf(c)>=0;
    }
 
        // Driver program
    public static void main(String[] args)
    {
        boolean isVowel = vowel('a');
         
                // Printing the output
                if(isVowel)
            System.out.println("Vowel");
        else
            System.out.println("Consonant");
    }
}
 
// This code is contributed by debjitdbb
Output
Vowel

This article is contributed by Astha Tyagi. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. 
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 




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