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