Java String charAt()

The Java String class charAt() method returns a char value at the given index number.

The index number starts from 0 and goes to n-1, where n is the length of the string. It returns StringIndexOutOfBoundsException, if the given index number is greater than or equal to this string length or a negative number.

Syntax

The method accepts index as a parameter. The starting index is 0. It returns a character at a specific index position in a string. It throws StringIndexOutOfBoundsException if the index is a negative value or greater than this string length.

Specified by

CharSequence interface, located inside java.lang package.

Internal implementation

public char charAt(int index) {  
       if ((index < 0) || (index >= value.length)) {  
           throw new StringIndexOutOfBoundsException(index);  
       }  
       return value[index];  
   }  

Java String charAt() Method Examples

Let's see Java program related to string in which we will use charAt() method that perform some operation on the give string.

FileName: CharAtExample.java

public class CharAtExample{
public static void main(String args[]){
String name="javatpoint";
char ch=name.charAt(4);//returns the char value at the 4th index
System.out.println(ch);
}}

Test it Now

Output:

Let's see the example of the charAt() method where we are passing a greater index value. In such a case, it throws StringIndexOutOfBoundsException at run time.

FileName: CharAtExample.java

public class CharAtExample{
public static void main(String args[]){
String name="javatpoint";
char ch=name.charAt(10);//returns the char value at the 10th index
System.out.println(ch);
}}

Output:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: 
String index out of range: 10
at java.lang.String.charAt(String.java:658)
at CharAtExample.main(CharAtExample.java:4)

Accessing First and Last Character by Using the charAt() Method

Let's see a simple example where we are accessing first and last character from the provided string.

FileName: CharAtExample3.java

public class CharAtExample3 {
	public static void main(String[] args) {
    String str = "Welcome to Javatpoint portal";    
    int strLength = str.length();    
    // Fetching first character
    System.out.println("Character at 0 index is: "+ str.charAt(0));    
    // The last Character is present at the string length-1 index
    System.out.println("Character at last index is: "+ str.charAt(strLength-1));    
    }
}

Output:

Character at 0 index is: W
Character at last index is: l

Print Characters Presented at Odd Positions by Using the charAt() Method

Let's see an example where we are accessing all the elements present at odd index.

FileName: CharAtExample4.java

public class CharAtExample4 {
	public static void main(String[] args) {
		String str = "Welcome to Javatpoint portal";		
		for (int i=0; i<=str.length()-1; i++) {
			if(i%2!=0) {
				System.out.println("Char at "+i+" place "+str.charAt(i));
			}
		}
	}
}

Output:

Char at 1 place e
Char at 3 place c
Char at 5 place m
Char at 7 place  
Char at 9 place o
Char at 11 place J
Char at 13 place v
Char at 15 place t
Char at 17 place o
Char at 19 place n
Char at 21 place  
Char at 23 place o
Char at 25 place t
Char at 27 place l

The position such as 7 and 21 denotes the space.

Counting Frequency of a character in a String by Using the charAt() Method

Let's see an example in which we are counting frequency of a character in the given string.

FileName: CharAtExample5.java

public class CharAtExample5 {
	public static void main(String[] args) {
		String str = "Welcome to Javatpoint portal";
		int count = 0;
		for (int i=0; i<=str.length()-1; i++) {
			if(str.charAt(i) == 't') {
				count++;
			}
		}
		System.out.println("Frequency of t is: "+count);
	}
}

Output:

Frequency of t is: 4

Counting the Number of Vowels in a String by Using the chatAt() Method

Let's see an example where we are counting the number of vowels present in a string with the help of the charAt() method.

FileName: CharAtExample6.java

// import statement
import java.util.*;

public class CharAtExample6
{  
ArrayList<Character> al;

// constructor for creating and 
// assigning values to the ArrayList al
CharAtExample6()
{
al = new ArrayList<Character>();  
al.add('A'); al.add('E');
al.add('a'); al.add('e');
al.add('I'); al.add('O');
al.add('i'); al.add('o');
al.add('U'); al.add('u');
}
 
// a method that checks whether the character c is a vowel or not   
private boolean isVowel(char c)
{
for(int i = 0; i < al.size(); i++)
{
if(c == al.get(i))
{
return true;
}
}
return false;
}
// a method that calculates vowels in the String s
public int countVowels(String s)
{
int countVowel = 0; // store total number of vowels
int size = s.length(); // size of string
for(int j = 0; j < size; j++)
{
char c = s.charAt(j);
if(isVowel(c))
{
// vowel found!
// increase the count by 1
countVowel = countVowel + 1;
}
}

return countVowel;
}
    
// main method
public static void main(String argvs[]) 
{  
// creating an object of the class CharAtExample6
CharAtExample6 obj = new CharAtExample6();

String str = "Javatpoint is a great site for learning Java.";  

int noOfVowel = obj.countVowels(str);

System.out.println("String: " + str);

System.out.println("Total number of vowels in the string are: "+ noOfVowel + "\n");  

str = "One apple in a day keeps doctor away.";

System.out.println("String: " + str);

noOfVowel = obj.countVowels(str);

System.out.println("Total number of vowels in the string are: "+ noOfVowel); 
}  
}  

Output:

String: Javatpoint is a great site for learning Java.
Total number of vowels in the string are: 16

String: One apple in a day keeps doctor away.
Total number of vowels in the string are: 13

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