Add Ex 18.15

Author: jsquared21

Diff for: Exercise_18/Exercise_18_15/Exercise_18_15.class

@@ -0,0 +1,41 @@
+/**********************************************************************************
+* (Occurrences of a specified character in a string) Rewrite Programming Exercise *
+* 18.10 using a helper method to pass the substring high index to the method.     *
+* The helper method header is:                                                    *
+*                                                                                 *
+* public static int count(String str, char a, int high)                           *
+**********************************************************************************/
+import java.util.Scanner;
+
+public class Exercise_18_15 {
+	/** Main method */
+	public static void main(String[] args) {
+		// Create a Scanner
+		Scanner input = new Scanner(System.in);
+
+		// Prompt the user to enter a string and a character
+		System.out.print("Enter a string and a character: ");
+		String[] str = input.nextLine().split("[ ]");
+
+		// Display the number of times the character occurs in the string
+		System.out.println("The character \'" + str[1] + "\' occurs " +
+			count(str[0], str[1].charAt(0)) + " times in \"" + str[0] + "\".");
+	}
+
+	/** Method counts the number of occurrences 
+	  * of a specified character in a string */
+	public static int count(String str, char a) {
+		return count(str, a, str.length() - 1);
+	}
+
+	/** Helper melthod used to pass the substring high index */
+	private static int count(String str, char a, int high) {
+		if (high < 0) // Base case
+			return 0;
+		else if (str.charAt(high) ==  a) {
+			return 1 + count(str, a, high - 1); // Recursive call
+		}
+		else
+			return count(str, a, high - 1); // Recursive call
+	}
+}