Question

I know I’m doing something stupid, but I cannot figure how to fix it.

The issue is inside the private method removeVowels particulry when using the vowels method.

The compiler gives

non-static variable vowels cannot be referenced from a static context

Here is my code:

   public class RecursionHW2 {

            String vowels;

            // Part (A) First way
            public static int upperCase(String myString){

                return upperCaseChecker(myString , 0 );
            }

            public static int upperCaseChecker(String myString, int index){

                int inc;

                //My Base Code
                if(myString.length() <= index) return 0;
                if(Character.isUpperCase(myString.charAt(index)) == true) inc= 1;
                    else inc= 0;

                return inc+upperCaseChecker(myString,index+1);
            }



            // First way of Solving part (B)
            public static int count(String str, char a)
            {
                if (str.length() == 0)
                    return 0;
                else if (str.charAt(0) == a)
                    return 1 + count(str.substring(1, str.length()), a);
                else
                    return count(str.substring(1, str.length()), a);
            }


            //Second way of solving part (B)
            public static int anotherCount(String myString, char myWord)
            {
                return anotherCount(myString, myWord, 0);
            }

            public static int anotherCount(String myString, char myWord, int index)
            {
                int inc;

                if (index >= myString.length())
                {
                    return 0;
                }

                if (myString.charAt(index) == myWord)  inc =1;
                    else
                        inc = 0;

                return inc + anotherCount(myString, myWord, index+1);
            }



            // part (C) solving
            public Boolean isSorted(int[] a, int n)
            {
            if(n == 0 || n == 1) return true;
            else
            return isSorted(a, n, 1);
            }

            private Boolean isSorted(int[] a, int n, int cur)
            {
                if(cur == n) return true;

                if(a[cur - 1] <= a[cur])
                    return isSorted(a, n, cur+1);
                else
                    return false;
            }



            //part (D) Solving
            public static String removeVowels(String myString)
            {
                return removeVowels(myString, "");
            }

            private static String removeVowels(String myString, String t)
            {
                if(myString.length() == 0) return t;

                if(vowels.contains(myString.charAt(0) + ""))
                    return removeVowels(myString.substring(1), t);
                else
                    return removeVowels(myString.substring(1), t + myString.charAt(0));
            }


        public static void main(String[] args){


            //I've wrote 2 ways to solve the Second Recursive Q2
            System.out.println("Method 1: Number of Occurence " + count("Hello  This is Mohammad Fadin",'o'));
        //  System.out.println("Method 2: Number of Occurence "+ anotherCount("Hello This is Mohammad Fadin",'o'));

            String s1 = "Hello WorlDD";
            System.out.println("Number of Upper Cases " + upperCase(s1));

            String s2 = "Hello";
            System.out.println("After Vowels Removed " + removeVowels(s2));
        }


    }

Answer 1

You’ve “infected” your code with static from your main method. In your main method you should do something like this, so you don’t have to make everything static:

public class RecursionHW2
{
  public static void main(String[] args)
  {
    RecursionHW2 rhw2 = new RecursionHW2();

    int count = rhw2.count("Hello world");

    // and so on
  }
}