Unit 4: Iteration

First the logical condition is evaluated - when it is true, the code inside the while loop will be executed. This repeats until the condition evaluates to false.

Question: Is it possible for a while loop to execute 0 times?

An infinite loop is a loop where the condition always evaluates to true.

Example of an infinite loop:

while (true)

   {do this stuff;}

The condition will always evaluate to true because true is always true.

A return statement can stop the execution of a loop and exit the method or constructor.

Read on while loops on Runestone academy and do the tasks on the page.
Do the practice tasks on Practice-It! related to the while loop - exercises 5.1 to 5.4.

My tasks:

Create a program that will identify whether an integer is or isn't evenly divisible by another integer.
Create a program that will identify the individual digits in an integer - the program will display the digits one by one to the shell.
Create a program that will keep asking for a word until the user has typed a sentinel (such as "exit") and it will keep alert the user every time they input a palindrome. Once the user has typed in the sentinel, the program will display the number of times the user has input a palindrome.
Have a look at the method below - try the understand the logic of the code and annotate it using comments in the code. Then, write a similar method that will return a student's first name based on the the student number input. All students' first names will be saved in one string, separated by a space.

import java.util.Scanner;

public class Main

    public static void Main()

           System.out.println("Type the month number:");

           Scanner keyboard= new Scanner (System.in);

           System.out.println(returnMonthName(keyboard.nextInt()));

    public static String returnMonthName(int month)

        String Months="January February March April May June July August September October November December ";

        int monthIndex=1;

        int stringIndex=0;

        int endOfMonthIndex=0;

        while (monthIndex<month)

                if (Months.substring(stringIndex,stringIndex+1).equals(" "))

                    monthIndex++;

                stringIndex++;

        endOfMonthIndex=stringIndex;

        while (!Months.substring(endOfMonthIndex,endOfMonthIndex+1).equals(" "))

                endOfMonthIndex++;

       return Months.substring(stringIndex,endOfMonthIndex);

Solutions:

public class Divisibility

    public Divisibility()

    public boolean evenlyDivisible(int number1,int number2)

        if (number1%number2==0)

            return true;

        else

            return false;

public class Main

    public static void Main()

        int number1=6;

        int number2=4;

        Divisibility d1=new Divisibility();

        String result="";

        if (d1.evenlyDivisible(number1,number2))

            result="is";

        else

            result="isn't";

        System.out.println("Number "+number1+" "+result+" evenly divisible by "+number2+".");

public class Main

    public static void Main()

        int number=256; //declaring and initializing a primitive variable

        Integer Number=new Integer(number); // creating a wrapper class so that you can convert the integer to a string

        String numberAsText=Number.toString(); // converting an integer to a string

        int index=0;// this will be the index used for traversing the string

        while (index<numberAsText.length())

                System.out.println(numberAsText.substring(index,index+1));

                index++;//increasing the index value by one for each iteration

import java.util.Scanner;

public class Main

    public static boolean isPalindrome(String word)

            int index=0;

            while (index<word.length())

                    if (!word.substring(index,index+1).equals(word.substring(word.length()-index-1,word.length()-index)))

                        System.out.println("Not a palindrome");

                        return false;

                    index++;

            System.out.println("This is a palindrome");

            return true;

    public static void Main()

    {Scanner keyboard=new Scanner(System.in);

     String input="";

     int noOfPalindromes=0;

     while (!input.equals("exit"))

            System.out.println("Input a word");

            input=keyboard.next();

            if (isPalindrome(input))

                    noOfPalindromes++;

     System.out.println("You typed "+noOfPalindromes+ " palindromes.");

»for« loops

Parts of a for-loop header:

for (initialization, Boolean expression, increment)

the initialization - e.g. int i=0
the Boolean expression - e.g. i<10
the increment e.g. i++

A sample for-loop:

for (int i=1;i<=10;i++)

   {System.out.println(i));

The initialization is executed only once - when the loop starts, before the first Boolean expression evaluation
the i variable in the for-loop above is called a loop control variable. It is commonly named "i" as it stands for "iteration", however, it can use any valid name here, such as "counter".
The increment statement gets executed after all the commands in the loop have been executed and just before the boolean expression gets evaluated again.
Any for-loop can be rewritten as a while-loop and vice versa.

Practice it online:

Developing algorithms using strings

This involves the following standard traversal (traversing through a string) algorithms to be familiar with:

finding one or more substrings that have a certain property
determine the number of substrings meeting a certain criterion
creating a new string that is a reversed copy of the original string

Tasks:

Create a program that will take a word as input and then will display the number of vowels in it. (Your vowels are "a", "e","i","o",u","y").

A one-loop solution:

import java.util.Scanner;

public class Main

    public static void Main()

    {   int vowelsCounter=0;

        Scanner keyboard=new Scanner(System.in);

        System.out.println("Type the word to count the vowels for:");

        String input=keyboard.next();

        String vowels="aeiouy";

            for (int i=0;i<input.length();i++)

                    if (vowels.indexOf(input.substring(i,i+1))>=0)

                        vowelsCounter++;

        System.out.println("The word "+input+" includes "+vowelsCounter+" vowel/s.");

A two-loop solution:

import java.util.Scanner;

public class Main

    public static void Main()

    {   int vowelsCounter=0; // this is where we store the vowels count

        Scanner keyboard=new Scanner(System.in);

        System.out.println("Type the word to count the vowels for:");

        String input=keyboard.next();

        String vowels="aeiouy"; //this stores all the vowels to look for

        String currentVowel=""; // this stores the current vowel from the list that we are checking

        String currentInputLetter=""; // this stores the current letter from the input text

        for (int i=0; i<vowels.length();i++)

            currentVowel=vowels.substring(i,i+1);// I change the vowel to look for here

            for (int j=0;j<input.length();j++)

                 currentInputLetter=input.substring(j,j+1);// I change the current letter of the input

                 if (currentInputLetter.indexOf(currentVowel)>=0)

                     vowelsCounter++;

        System.out.println("The word "+input+" includes "+vowelsCounter+" vowel/s.");

Practice it online:

Nested iteration

We speak of nested iteration when there is a loop inside another loop.
The inner loop must finish all its iteration before the outer loop can proceed to the next iteration.

A nested loop example:

// prints the multiplication facts up to 10*10

for (int i=1;i<=10;i++)

    for (int j=1;j<=10;j++)

        System.out.println(i+"*"+j-"="+i*j);

Practice it online:

Informal code analysis

You should be able to tell how many times a certain statement got executed during the running of a loop.

You should also be able to trace how a certain variable contents change during the running of a loop. For this it is useful to use a tracing table.

Practice it online:

consumer review lab

You can find the student notes to this lab here.

Activity 2 - pseudocode

totalSentiment()

Call the textToString() method with your review saved as a text file as input.
Make sure you save the outcome of step 1 in an appropriate variable, so that you can use it later.
Get rid of all the punctuation in the review, now saved in a string. For this you can either use the getPunctuation() method or you can devise your own way of doing this, such as by traversing the whole string and copying it to a new string, character by character, provided the character is not on the "black list", which would be the list of all the punctuation that there is.
Now go over the review, one word at a time (you are not supposed to use the split() method, use your spaces as a sentinel) and fetch the sentiment value for each word by using the sentimentVal() method which you need to add the running total. Also, keep track of the number of words you have evaluated
Calculate the average sentiment value by dividing the total sentiment value by the number of the words evaluated.
Return the average sentiment value.

starRating()

call totalSentiment() to find the sentiment value of the review
evaluate the score and assign it a value based on some thresholds - use a series of if-else-if statements for this.

(Based on official AP Computer Science A teacher materials)

Activity 2: totalSentiment() - my solution:

  public static double totalSentiment(String fileName)

      int WordCount=0;

      String Word="";

      double totalSentimentValue=0.0;

      String ReviewText=textToString(fileName);

      String TextWithoutPunctuation="";

      //removing punctuation:

      for (int i=0; i<ReviewText.length();i++)

            if (getPunctuation(ReviewText.substring(i,i+1))=="")

                TextWithoutPunctuation+=ReviewText.substring(i,i+1);

            else

                TextWithoutPunctuation+=" ";

      //fetching the sentiment value for each word and adding it to the total

      for (int j=0; j<TextWithoutPunctuation.length();j++)

           if (!TextWithoutPunctuation.substring(j,j+1).equals(SPACE))

                Word+=TextWithoutPunctuation.substring(j,j+1);

           else

               System.out.println(sentimentVal(Word));

               totalSentimentValue+=sentimentVal(Word);

               WordCount++;

               Word="";

      //calculating the average sentiment value and returning it:

      return totalSentimentValue/WordCount;

Activity 2: starRating() - my solution:

  public static int starRating(String fileName)

     double totalSentimentValue=totalSentiment(fileName);

     if (totalSentimentValue>2)

        return 4;

     else if (totalSentimentValue>1)

        return 2;

     else if (totalSentimentValue>0)

        return 1;

     else

        return 0;

Activity 3: pseudocode:

fakeReview() method:

Use the provided textToString() method to generate a string from the review text file.
Create another string that you will use to store the fake review - initialize it as blank.
Traverse the words in the original review and once it comes across an adjective (you have them flagged with a star), do the following:
- store the ending punctuation in a variable
- fetch a random adjective using the randomAdjective() method and store the outcome in a variable
- Append the random adjective with ending punctuation to the fake review string.
If the word is not an adjective, just append it to the fake review string as it is.
When finished processing all words, return the finished fakeReview string.

(Based on official AP Computer Science A teacher materials)

Activity 3 - my solution

  public static String fakeReview(String fileName)

      String Word="";

      String ReviewText=textToString(fileName);

      String FakeReview="";

      String EndingPunctuation="";

      String RandomAdjective="";

//traverse through the review string, keep building the word until you hit a space:

      for (int i=0;i<ReviewText.length();i++)

        {    if (!ReviewText.substring(i,i+1).equals(SPACE))

                Word+=ReviewText.substring(i,i+1);

//when the whole word has been read:

           else

{//look only for words that start with a star (i.e. adjectives):

               if (Word.substring(0,1).equals("*"))

                   EndingPunctuation=getPunctuation(Word);

                   RandomAdjective=randomAdjective();

//add a random adjective to the review with the original punctuation (if any) plus a space:

                   FakeReview+=RandomAdjective+EndingPunctuation+" ";1

               else

                   FakeReview+=Word+" ";

               Word="";

      return FakeReview;

Activity 4 - pseudocode

Traverse the review string, looking for words (use the code in Activity 3 for this), when it comes across an adjective (flagged with a star), calls the sentimentVal() method for it and save the corresponding sentiment value in a variable.
If creating a more positive review, call the randomPositiveAdj() method, for a more negative review call the randomNegativeAdj() method. Find the sentiment value of the random adjective and see if it is higher or lower than the original adjective's sentiment value. If you are trying to create a more positive review, keep calling the randomPositiveAdj() method until it has returned an adjective that has a higher sentiment value than the original adjective. If you are trying to create a more negative review, keep calling the randomNegativeAdj() method until its sentiment value is lower than that of the original adjective.
Replace the original adjective with the new one in the output string
Once the whole review has been processed, return the modified review string.

(Based on official AP Computer Science A teacher materials)

Activity 4 - my solution

public static String fakeNegativeReview(String fileName)

      String Word="";

      String ReviewText=textToString(fileName);

      String FakeNegativeReview="";

      String EndingPunctuation="";

      String RandomAdjective="";

      double SentimentValue=0;

      for (int i=0;i<ReviewText.length();i++)

// in this branch we deal with complete words:

{ if ((ReviewText.substring(i,i+1).equals(SPACE)) || (i==ReviewText.length()-1))

//this if is to take care of the last word in the file which isn't followed by a space:

if (i==ReviewText.length()-1)

                   Word+=ReviewText.substring(i,i+1);

               if (Word.substring(0,1).equals("*"))

                   EndingPunctuation=getPunctuation(Word);

                   RandomAdjective=randomNegativeAdj();

                   while (sentimentVal(Word)<sentimentVal(RandomAdjective))

                        RandomAdjective=randomNegativeAdj();

                   FakeNegativeReview+=RandomAdjective+EndingPunctuation+" ";

//In this branch we are adding characters to the word:

else

                   FakeNegativeReview+=Word+" ";

               Word="";

             else

                Word+=ReviewText.substring(i,i+1);

      System.out.println(FakeNegativeReview);

      return FakeNegativeReview;

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