Question

Write an application with two classes USING JAVA METHODS HAVE TO BE CREATED USING RECURSION. First class named Recursion has the following three recursive methods:

// PRECONDITION n is positive integer. Method sumTerms returns sum of terms that are

// reciprocal values of first n integers, with  alternating signs.     

// For example,  sumTerms(7) returns  the following:  1/1 – 1/2  + 1/3 – 1/4  + 1/5 -1/6 + 1/7.

// Terms with an odd denominator have positive sign, and terms with even denominator have

// negative sign.  

• double sumTermsRec(int n)

// PRECONDITION n is non-negative integer denoting the number of occupied positions in the

// array words.   Method printsWordsRec prints each String element in the array words

// together with its string length in the same order as they appear in the array words

• void printWordsRec (String[] words, int n)

// PRECONDITION n is non-negative integer denoting the number of occupied positions in the

// array words.   Method printsWordsReverseRec prints each String element in the array

// words together with its length. Elements are printed in reverse  order than they apper in

// the  array words.

• void printWordsReverseRec (String[] words, int n)

If array words has first three elements assigned values "Paris", Athens ", "Rome" method  printWordsRec should print

Paris 5

Athens 6

Rome 4

and  method printWordsReverseRec should print

Rome 4

Athens 6

Paris 5.

Class Tester has main method in it. In the main method invoke each of the three methods from class Recursion. Program outcome must provide English explanation which method is invoked and what is the result, and/or what method does.

Answer 1

PLEASE NOTE : FEEL FREE TO ASK ANY DOUBTS by COMMENTING

• I'm little bit confused of condition "Program outcome must provide English explanation which method is invoked and what is the result, and/or what method does."
  • We are using recursion, if we print about function it prints for every call. So, i'm not printing about function explanation.
  • Let me know if you have any queries regarding this
• I'm just calling the functions and printing result in Tester code.
• if you want me to change anything or if you face any troubles, please let me know by commenting.
• I used comments for better understanding. Comments starts with ' // '
• Please refer to the screenshot of the code to understand the indentation of the code

Language : Java

Filename : Recursion.java , Tester.java

IDE : Java Eclipse

:::::::::::::::::::::::::::::::::::::::::::: CODE ::::::::::::::::::::::::::::::::::::::::

Recursion.java

public class Recursion {
   // this method is used to return
   // reciprocal values of first n integers, with alternating signs
   public double sumTermsRec(int n) {
       // if n value is 0, return 0
       if(n==0) {
           return 0;
       }
       // if n is even, return negative value with calling next value
       if(n%2 == 0) {
           return -(1.0/n)+sumTermsRec(n-1);
       }
       // if n is odd, return positive value with calling next value
       return (1.0/n)+sumTermsRec(n-1);
   }

   // this method is used to print array values from first to last
   public void printWordsRec(String[] words, int n) {
       // if n value is more than 0
       if(n > 0) {
           // call function for next index of n which is n-1
           printWordsRec(words,n-1);
           // print string at index n-1
           System.out.println(words[n-1]+" "+words[n-1].length());
       }
   }

   // this method is used to print array values from last to first
   public void printWordsReverseRec (String[] words, int n) {
       // if n value is more than 0
       if(n > 0) {
           // print string at index n-1
           System.out.println(words[n-1]+" "+words[n-1].length());
           // call function for next index of n which is n-1
           printWordsRec(words,n-1);
       }
   }
}

Tester.java

public class Tester {
   public static void main(String[] args) {
       // create Recursion class instance
       Recursion r = new Recursion();

       // call sumTermsRec function with value 7
       System.out.println(r.sumTermsRec(7));

       // array of strings
       String[] words = {"Paris", "Athens","Rome"};

       // call printWordsRec to print first to last
       r.printWordsRec(words,words.length);

       // call printWordsReverseRec to print last to first
       r.printWordsReverseRec(words,words.length);
   }
}

:::::::::::::::::::::::::::::::::::::::::::: OUTPUT ::::::::::::::::::::::::::::::::::::::::

X Console X <terminated> Tester [Java Application] C:\Program Files\Java\jdk-13\bin\javaw.exe 0.7595238095238095 Paris 5 Athens 6 Rome 4 Rome 4 Paris 5 Athens 6

:::::::::::::::::::::::::::::::::::::: CODE in EDITOR ::::::::::::::::::::::::::::::::::

Recursion.java

2 3 Recursion.java X Tester.java 1 public class Recursion // this method is used to return //reciprocal values of first n integers, with alternating signs public double sumTermsRec(int n) { 5 // if n value is O, return o if(n==0) { 7 return 0; 46 6 8 } 9 10 11 //if n is even, return negative value with calling next value if(n%2 == 0) { return -(1.0/n)+sumTermsRec(n-1); 12 } 13 14 15 I/if n is odd, return positive value with calling next value return (1.0/n)+sumTermsRec(n-1); } 16 17 180 19 20 // this method is used to print array values from first to last public void printWordsRec(String[] words, int n) { // if n value is more than if(n > 0) { // call function for next index of n which is n-1 printWordsRec(words,n-1); // print string at index n-1 System.out.println(words [n-1]+" "+words[n-1].length()); 21 22 23 24 25 } 26 } 27 28 290 30 31 32 33 34 35 36 37 38 } // this method is used to print array values from last to first public void printWordsReverseRec (String[] words, int n) { // if n value is more than a if(n > 0) { // print string at index n-1 System.out.println(words[n-1]+" "+words[n-1].length(); // call function for next index of n which is n-1 printWordsRec(words, n-1); } } лв

Tester.java

26 4 Recursion.java X Tester.java X 1 public class Tester { public static void main(String[] args) { 3 // create Recursion class instance Recursion r = new Recursion(); 5 // call sumTerms Rec function with value 7 7 System.out.println(r.sumTermsRec(7)); 8 9 // array of strings 10 String[] words = {"Paris", "Athens", "Rome"}; 11 12 // call printWordsRec to print first to last 13 r.printWordsRec(words, words.length); 14 15 // call printWords ReverseRec to print last to first 16 r.printWordsReverseRec(words, words.length); 17 18 } 19 }

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