Question

Challenge Level For the Challenge level, implement the following enhancements: • Multiple-word items • Input validation • Single item removal The two extra-credit points for the Challenge level are allocated as follows: • one for multiple-word items, checking for blank input checking for unrecognized commands • one for single-item removal Multiple-Word Items Update this application to accept multi-word shopping list items. This will require you to update the delimiter used by the Scanner object. The useDelimiter method will allow you to change the delimiter character. You can use the newline character as the new delimiter: scan.useDelimiter("\n"); Notice that this enhancement adds additional input validation. You will need to check the input. If input isn't blank, process it as either a command or an item for the list. If the input is blank, report the error. For example: Enter your item or command: peanut butter Enter your item or command: Shopping list items cannot be blank. Note: This enhancement does not count toward Challenge points by itself, It is a necessary modification for support of removing single items from the list. Invalid Commands In the scheme that we are using, all commands start out with a hyphen. However, it is possible for the user to type an unrecognized command, for example-w. The given implementation will treat this as an item for the list, rather than as an unrecognized command. Update the driver so that, if the user types in something beginning with a hyphen that is not one of the recognized commands, print out an error message, print out the list of commands. Enter your item or command: -W Unrecognized command: -W Here are the list of commands: -p: Print the List -e : Empty the List -X: Exit -h : Print this command list Enter your item or command: Remove a single item Add a command to the menu that removes a single item from the list. There are two forms that this command could take. You may implement either form of single-item removal. Implementing both will count toward additional Challenge points.

Below is the code for the class shoppingList, I need to enhance it to accomplish the challenge level as stated in the description above.

public class ShoppingList {  
private java.util.Scanner scan;
private String[] list;
private int counter;

public ShoppingList() {
scan = new java.util.Scanner(System.in);
list = new String[10];
counter = 0;
}
public boolean checkDuplicate(String item) {
for(int i = 0; i < counter; i++) {
if (list[i].equals(item))
return true;
}
return false;
}
public void printList() {
System.out.println("Your shopping list:");
if(counter == 0)
System.out.println(" * No items in list.");
for(int i = 0; i < counter; i++) {
System.out.println(" " + (i + 1) + ". " + list[i]);
}   
}
public void addToList(String item) {
if(counter < 10) {
if(!checkDuplicate(item))
list[counter++] = item;
else
System.out.println("Duplicte item " + item + " not added to list.");
} else {
System.out.println("List is full. Item " + item + " not added to list.");
}
}
public void emptyList() {
list = new String[10];
System.out.println("All items removed from list.");
counter = 0;
}
public String getInput() {
System.out.print("Enter your item or command: ");
return scan.next().trim();
}
public void printWelcome() {
System.out.println("Welcome to the my Shopping List Program.");
}
public void printThankYou() {
System.out.println("Thank you for using the my Shopping List Program.");
}
public void printHelp() {
System.out.println("Here are the list of commands:");
System.out.println(" -p : Print the list");
System.out.println(" -e : Empty the list");
//System.out.println(" -r n : Remove the nth item from the list");
System.out.println(" -x : Exit the application");
System.out.println(" -h : Print this command list");
}
public void go() {
String input;
printWelcome();
printHelp();
input = getInput();
while( ! input.equals("-x")) {
switch(input) {
case "-h":
printHelp();
break;
case "-p":
printList();
break;
case "-x":
break;
case "-e":
emptyList();
break;
default:
addToList(input);
}
input = getInput();
}
printThankYou();
}
public static void main(String[] args) {
ShoppingList list;
list = new ShoppingList();
list.go();
}
}

Answer 1

Working code implemented in Java and appropriate comments provided for better understanding:

Source code for ShoppingList.java:

/**
* The ShoppingList class enables the use of an interactive shopping
* list using a partially-filled array. This version of the class can
* only hold up to ten items.
*/
public class ShoppingList {
  
private java.util.Scanner scan;
private String[] shop;
private int index;
  
/**
* Simple constructor that instantiates the class fields
*/
public ShoppingList() {
// Used nextLine method in getInput instead of useDelimiter in constructor.
// Fixed a bug where if the first input is blank, an error message was not
// printed.
scan = new java.util.Scanner(System.in);
shop = new String[10];
index = 0;
}
  
/**
* Prints out items currently stored in the shopping list. Does
* not print out empty (null) items.
*/
public void printList() {
System.out.println("Your shopping list:");
// print the list
if (index > 0) {
for (int i = 0; i < index; i++) {
System.out.println(" " + (i+1) + ". " + shop[i]);
}
} else {
System.out.println(" * No items on list.");
}
}
  
/**
* Adds an item to the shopping list at the next available index.
* @param item The item being added to the list
*/
public void addToList(String item) {
shop[index ++] = item;
}
  
/**
* Removes every item from the list and resets the index field.
*/
public void emptyList() {
// change all values to null
for (int i = 0; i < index; i++) {
shop[i] = null;
}
index = 0;
}
  
/**
* Given an integer, removes the item at that index
* from the shopping list.
* @param num An index in the list (1-10)
*/
public void removeFromList(int num) {
// error if num is bigger than index or smaller than 1
if (num > index || num < 1) {
System.out.println(" * No item " + num + " in shopping list");
} else {
shop[num-1] = null;
  
// reorder remaining values
for (int i = num; i < index; i++) {
shop[i-1] = shop[i];
}
  
// update index field
index--;
}
}
  
/**
* Given a string, removes any equivalent items from the list. If
* the string is not found, checks if the string is numerical and calls
* the int version of the method, otherwise prints an error.
* @param item The item to be removed
*/
public void removeFromList(String item) {
int nullIndex = index;
boolean itemFound = false;
// remove item
for (int i = 0; i < index; i++) {
if (shop[i].equals(item)) {
shop[i] = null;
// user index used for nullIndex
nullIndex = i + 1;
itemFound = true;
}
}
  
// reorder remaining values
for (int i = nullIndex; i < index; i++) {
shop[i-1] = shop[i];
}
  
// update index field
if (itemFound) {
index--;
} else if (isNumeric(item)) {
removeFromList(Integer.parseInt(item));
} else {
System.out.println(" * No item " + item + " in shopping list");
}
}

/**
* Tests if a string input can be converted into an integer.
* Helper function for the removeFromList method.
* @param input User input
* @return A boolean value describing if the input is numerical
*/
private boolean isNumeric(String input) {
try {
Integer.parseInt(input);
} catch(NumberFormatException error) {
return false;
}
return true;
}
  
/**
* Tests if a given item is already in the shopping list.
* @param item The item to check
* @return a boolean value describing whether the item is in the list
*/
public boolean isDuplicate(String item) {
boolean duplicate = false;
for (String thing : shop) {
if (item.equals(thing)){
duplicate = true;
}
}
return duplicate;
}
  
/**
* Gets user input from the keyboard.
* @return The user's input
*/
public String getInput() {
System.out.print("Enter your item or command: ");
return scan.nextLine().trim();
}
  
/**
* Prints a greeting. Used when the program is started.
*/
public void printWelcome() {
System.out.println("Welcome to the XYZ Shopping List Program.");
}
  
/**
* Prints a goodbye message. Used when the program ends.
*/
public void printThankYou() {
System.out.println("Thank you for using the XYZ Shopping List Program.");
}
  
/**
* Prints a help menu that displays the supported commands of the
* shopping list.
*/
public void printHelp() {
System.out.println("Here are the list of commands:");
System.out.println(" -p : Print the list");
System.out.println(" -e : Empty the list");
System.out.println(" -r n : Remove the nth item or the item " +
"n from the list");
System.out.println(" -x : Exit the application");
System.out.println(" -h : Print this command list");
}
  
/**
* The driver method of the class. This method is responsible for all
* program-user interactions.
*/
public void go() {
String input;
  
printWelcome();
printHelp();
input = getInput();
while( ! input.equals("-x")) {
switch(input) {
case "":
System.out.println("Shopping list items cannot be blank.");
break;
case "-h":
printHelp();
break;
case "-p":
printList();
break;
case "-x":
break;
case "-e":
emptyList();
break;
default:
// case "-r n"
if (input.startsWith("-r ") && input.length() > 3) {
String subInput = input.substring(3, input.length());
removeFromList(subInput);
  
// identify unknown commands
} else if (input.startsWith("-")) {
System.out.println("Unrecognized command: " + input);
printHelp();
  
// identify duplicates
} else if (isDuplicate(input)) {
System.out.println("Duplicate item " + input +
" not added to the list.");
  
// check if list is full
} else if (index > 9) {
System.out.println("List is full. Item " + input +
" not added to the list.");
  
// if tests pass, add input to list
} else {
addToList(input);
}
}
input = getInput();
}
printThankYou();
}
  
/**
* The application method. Calls the driver function to start the program.
* @param args The command line arguments
*/
public static void main(String[] args) {
ShoppingList list;
  
list = new ShoppingList();
list.go();
}
}

Sample Output Screenshots:

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