How to count the number of occurrences of a character in a string in java

Count the number of occurrences of a character in a string is good programming questions . It is ask in colleges and schools mostly. This question also asked in many times in interviews. 

Method 1:

We can count number of occurrences of a character in a string with the help of indexOf() method.

package com.javaproficiency;

public class CountCharOccurance {

public static void main(String[] args) {

String str = "javaproficiencyexamplebyannu";

 

    String findStr = "a";

    int lastIndex = 0;

    int counter = 0;

 

    while (lastIndex != -1) {

 

     lastIndex = str.indexOf(findStr, lastIndex);

 

     if (lastIndex != -1) {

      counter++;

      lastIndex += findStr.length();

 

     }

    }

    System.out.println(counter);

}

}

Output: 

4

Method 2:

In this example we will use charAt() method of string for count number of occurrences of a character in a string .

package com.javaproficiency;

public class CountCharOccurancejava {

public static void main(String[] args) {

String s = "javaproficiencyexamplebyannu";

int counter = 0;

for( int i=0; i<s.length(); i++ ) {

   if( s.charAt(i) == 'a' ) {

       counter++;

   } 

}

System.out.println( counter );

}

}

Output:

4