Here is an example that check if the input string contains equal number of A's and B's.

class  StringEx
{
    public static void main(String[] args) 
    {
        String st="ABRA KA DABRA";
        int countA=0,countB=0;
        for(int i=0;i<st.length();i++){
            char ch=st.charAt(i);
            if(ch=='A'){
                countA++;
            }
            if(ch=='B'){
                countB++;
            }
        }
        if(countA==countB){
            System.out.println("No of A's and B's are equal in string");
        }
        else{
            System.out.println("No of A's and B's are not equal in string");
        }
    }
}

thank you so much for quick response.very big help