Please Use Java:

In this lab a grocery list editor with undo functionality is implemented.

Step 1: Inspect the UndoCommand abstract base class

The read-only UndoCommand.java file has a declaration for the UndoCommand abstract base class. Access UndoCommand.java by clicking on the orange arrow next to LabProgram.java at the top of the coding window. The UndoCommand class represents a command object: an object that stores all needed information to execute an action at a later point in time. For this lab, a command object stores information to undo a grocery list change made by the user.

Step 2: Inspect the incomplete GroceryList class

The GroceryList class is declared in GroceryList.java. Two protected fields are declared:

An ArrayList of strings for list items

A stack of UndoCommand references for undo commands

Note that the addWithUndo() method is already implemented. The method adds a new item to the list and pushes a new RemoveLastCommand object onto the undo stack.

Step 3: Implement RemoveLastCommand's execute() method

The RemoveLastCommand class inherits from UndoCommand and is declared in RemoveLastCommand.java. When a RemoveLastCommand object is executed, the string ArrayList's last element is removed. So when the user appends a new item to the grocery list, a RemoveLastCommand is pushed onto the stack of undo commands. Popping and executing the RemoveLastCommand then removes the item most recently added by the user.

RemoveLastCommand's sourceList field and constructor are already declared:

sourceList is a reference to a GroceryList object's ArrayList of strings.

The constructor takes a reference to an ArrayList of strings as a parameter, and assigns sourceList with the reference.

Implement RemoveLastCommand's execute() method to remove sourceList's last element.

Step 4: Implement GroceryList's executeUndo() method

Implement GroceryList's executeUndo() method to do the following:

Pop an UndoCommand off the undo stack

Execute the popped undo command

File LabProgram.java has code that reads in a list of commands, one per line, that allow for basic testing of basic operations. So after implementing executeUndo(), run your program with the following input:

add bananas add grapes add strawberries print undo print undo print quit 

Verify that the corresponding output is:

0. bananas 1. grapes 2. strawberries 0. bananas 1. grapes 0. bananas 

The program's output does not affect grading, so additional test cases can be added, if desired.

Submitting code written so far to obtain partial credit is recommended before proceeding to the next step.

Step 5: Implement the SwapCommand class and GroceryList's swapWithUndo() method

Implement the SwapCommand class in SwapCommand.java. The class itself is declared, but no class members yet exist. Add necessary fields and methods so that the command can undo swapping two items in the grocery list.

Implement GroceryList's swapWithUndo() method. The method swaps list items at the specified indices, then pushes a SwapCommand, to undo that swap, onto the undo stack.

Step 6: Implement the InsertAtCommand class and GroceryList's removeAtWithUndo() method

Implement the InsertAtCommand class in InsertAtCommand.java. Add necessary fields and methods so that the command can undo removing a grocery list item at an arbitrary index.

Implement GroceryList's removeAtWithUndo() method. The method removes the list item at the specified index, then pushes an InsertAtCommand, to undo that removal, onto the undo stack.

LabProgram.java:

import java.io.PrintWriter; import java.util.Scanner; import java.util.ArrayList; import java.util.Arrays;

public class LabProgram { public static void main(String[] args) { Scanner scnr = new Scanner(System.in); GroceryList groceryList = new GroceryList(); PrintWriter testFeedback = new PrintWriter(System.out);

String command; boolean quit = false;

while (!quit) { command = scnr.nextLine();

// Process user input if (command.equals("print")) { groceryList.print(testFeedback); } else if (0 == command.indexOf("add ")) { groceryList.addWithUndo(command.substring(4)); } else if (0 == command.indexOf("removeat ")) { int index = Integer.parseInt(command.substring(9)); groceryList.removeAtWithUndo(index); } else if (0 == command.indexOf("swap ")) { int index1 = -1, index2 = -1; String str = command.substring(5);

if (str.indexOf(" ") != -1) { index1 = Integer.parseInt(str.substring(0, 1)); index2 = Integer.parseInt(str.substring(2, 3)); groceryList.swapWithUndo(index1, index2); } else { System.out.print("\"swap\" command requires two indices, separated "); System.out.println("by a space. Ex: swap 2 5"); } } else if (command.equals("undo")) { if (0 == groceryList.getUndoStackSize()) { System.out.println("Cannot execute undo because undo stack is empty"); } else { groceryList.executeUndo(); } } else if (command.equals("quit")) { quit = true; } else { System.out.println("Unknown command: " + command); } testFeedback.flush(); } } }

UndoCommand.java:

public abstract class UndoCommand { public abstract void execute(); }

RemoveLastCommand.java

import java.util.ArrayList;

public class RemoveLastCommand extends UndoCommand { private ArrayList sourceList; public RemoveLastCommand(ArrayList lst) { this.sourceList = lst; } @Override public void execute() { sourceList.remove(sourceList.size() - 1); } }

SwapCommand.java:

import java.util.ArrayList;

public class SwapCommand extends UndoCommand { private ArrayList sourceList; private int index1, index2; private String temp;

public SwapCommand(ArrayList lst, int i1, int i2) { this.sourceList = lst; this.index1 = i1; this.index2 = i2; } @Override public void execute() { temp = sourceList.get(index1); sourceList.set(index1, sourceList.get(index2)); sourceList.set(index2, temp); }

}

InsertAtCommand.java:

import java.util.ArrayList;

public class InsertAtCommand extends UndoCommand { private ArrayList sourceList; private int index; private String item;

public InsertAtCommand(ArrayList lst, int i, String it) { this.sourceList = lst; this.index = i; this.item = it; } @Override public void execute() { sourceList.add(index, item); } }

GroceryList.java:

import java.util.*; import java.io.PrintWriter;

public class GroceryList { protected ArrayList listItems = new ArrayList(); protected Stack undoStack = new Stack();

public void addWithUndo(String newItemName) { // Add the new list item listItems.add(newItemName);

// Make an undo command that removes the last item and push onto stack undoStack.push(new RemoveLastCommand(listItems)); }

public void removeAtWithUndo(int removalIndex) { if (removalIndex >= 0 && removalIndex < listItems.size()) { String removedItem = listItems.remove(removalIndex); undoStack.push(new InsertAtCommand(listItems, removedItem, removalIndex)); } else { System.out.println("Index out of bounds. Cannot remove the item."); } }

public void swapWithUndo(int index1, int index2) { if (index1 >= 0 && index1 < listItems.size() && index2 >= 0 && index2 < listItems.size()) { Collections.swap(listItems, index1, index2); undoStack.push(new SwapCommand(listItems, index1, index2)); } else { System.out.println("Index out of bounds. Cannot swap the items."); } }

// Pop and execute the command at the top of the stack public void executeUndo() { if (undoStack.empty()) { System.out.println("Cannot execute undo because undo stack is empty."); } else { undoStack.pop().execute(); } }

final int getListSize() { return listItems.size(); }

final int getUndoStackSize() { return undoStack.size(); }

final ArrayList getVectorCopy() { return listItems; }

public void print(PrintWriter outputStream) { for (int i = 0; i < listItems.size(); i++) { outputStream.write(i + ". " + listItems.get(i) + " "); } } }