Java String indexOf()

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. 
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'));    }}
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));    }}
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));    }}
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));    }}
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
Vowel
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