Question

Create a new Java project called 1410_Recursion. Add a package recursion and a class Recursion. Include the following three static methods described below. However, don't implement them right away. Instead, start by returning the default value followed by a // TODO comment.

1. public static int sumOfDigits(int n)
   This method returns the sum of all the digits.
   sumOfDigits(-34) -> 7
   sumOfDigits(1038) -> 12
   
2. public static int countSmiles(char[] letters, int index)
   This method counts the number of colons followed by a closing parenthesis.
   countSmiles([:,), ,L,i,f,e, ,i,s, ,g,o,o,d, ,:,)], 0) -> 2
   countSmiles([H,a,p,p,y, ,D,a,y, ,:,),:,),:,),!], 0) -> 3
   countSmiles([a,:,b,(,c,),:, ,),e], 0) -> 0
   
3. public static String toUpper(String str)
   This method separates all characters by a space and changes all lowercase letters to uppercase letters.
   E.g. "Hi there!" returns "H I T H E R E !"
   Hint: Class Character (Links to an external site.) includes a method toUpperCase (Links to an external site.)​
   

Create a second source folder called test. It should include a class RecursionTest. That's where you will write the JUnit tests for the three methods above.

• Each of the three methods should have at least eight corresponding JUnit tests.
• Choose test data deliberately to provide thorough testing that covers as many potential problems as possible.

Once you have written the JUnit tests, implement the methods.

Answer 1

Recursion.java

public class Recursion {
        
        public static int sumOfDigits(int n) {
                // we cannot sum -ve elements so calculating absolute
                n = Math.abs(n);
                // if n is 0 then return 0
                // else calculate sum of digits
                if(n==0)
                        return 0;
                return n%10+sumOfDigits(n/10);
                
        }
        
        public static int countSmiles(char[] letters, int index) {
                
                // if index is 0 then we cannot count further 
                if(index==letters.length)
                        return 0;
                
                // checking index if it is less than length of letters
                // and checking for smile characters
                if(index+1 < letters.length && 
                                letters[index]==':'&& letters[index+1]==')') {
                        
                        // if smile found add 1
                        return 1 + countSmiles(letters, index+2);
                }else {
                        return countSmiles(letters, index+1);
                }
                
        }
        
        public static String toUpper(String str) {
                
                // if length is 1 return the upper case 
                if(str.length()==1) {
                        return str.toUpperCase();
                }
                // converting to upper case character
                char upper =Character.toUpperCase(str.charAt(0));
                
                // concatenating recursively
                return upper+" "+toUpper(str.substring(1,str.length()));
                
                
        }
}

RecursionTest.java

import static org.junit.Assert.*;
import org.junit.Test;

public class RecursionTest {

        @Test
        public void DigitsSumTest() {
                
                int sum;
                
                // Test1
                // returns the calculated sum
                sum = Recursion.sumOfDigits(-34);
                // tests whether the sum is equal
                assertEquals(7, sum);
                
                // Test 2
                sum = Recursion.sumOfDigits(1038);
                assertEquals(12, sum);
                
        }
        
        @Test
        public void CountSmilesTest() {
                int count;
                char[] ch;
                
                // Test 1
                // character array
                ch = new char[] {':',')',' ','L','i','f','e',
                                ' ' ,'i','s',' ' ,'g','o','o','d',' ',':',')'};
                // returns the calculated counted smiles
                count = Recursion.countSmiles(ch, 0);
                assertEquals(2, count);
                
                // Test 2
                ch = new char[] {'H','a','p','p','y',' ','D',
                                'a' ,'y',' ',':' ,')',':',')',':',')','!'};
                count = Recursion.countSmiles(ch, 0);
                assertEquals(3, count);
                
                // Test 3
                ch = new char[] {'a',':','b','(','c',')',':',' ' ,')','e'};
                count = Recursion.countSmiles(ch, 0);
                assertEquals(0, count);
                
        }
        @Test
        public void UpperTest() {
                String s;

                // test 1
                s= "Hi there!";
                
                // returns the upper case letter
                s = Recursion.toUpper(s);
                // tests whether it is same
                assertEquals(s,"H I   T H E R E !");
                
        }
        
}

Code

Recursion.java

RecursionTest.java

Output