Procedural abstraction Information hiding

Procedural abstraction Information hiding Abstract Data Types (ADT)

Figure 3.1 Isolated tasks: the implementation of task T does not affect task Q

Figure 3.2 A slit in the wall

Add data to a data collection Remove data from a data collection Ask questions about the data in a data collection Operations on data

An abstract data type -- a collection of data and a set of operations on that data. A data structure -- a construct within a programming language that stores a collection of data. ADTs vs. Data Structures

Figure 3.3 A dispenser of chilled water, crushed ice, and ice cubes

Figure 3.4 A wall of ADT operations isolates a data structure from the program that uses it

Figure 3.5 A grocery list

Create an empty list. Determine whether a list is empty. Determine the number of items on a list. Add an item at a given position in the list. Remove the item at a given position in the list. Remove all the items from the list. Retrieve (get) the item at a given position in the list. ADT List Operations

createList() isEmpty() size() add(index, item) remove(index) removeAll() get(index) ADT List Operations-Pseudocode

To get a list of the following items: milk, eggs, butter, apples, bread, chicken First, declare aList as an object of List Then, aList.createList() aList.add(0, milk) aList.add(1, eggs) aList.add(2, butter) aList.add(3, apple) aList.add(4, bread) aList.add(5, chicken) ADT List Operations-Pseudocode

After the following statement aList.add(3, nuts) The list will be milk, eggs, butter, nuts, apples, bread, chicken If the following operation is performed aList.remove(4) The list will be milk, eggs, butter, nuts, bread, chicken ADT List Operations-Pseudocode

Once the behavior (basic operations) of an ADT is designed, access and manipulation of the ADT’s data can be defined based on its operations. displayList - displays all the items on the list aList. replace - replaces the ith item on the list aList with newItem. Access and Manipulation of ADT’s Data

displayList(aList) for (index = 0 through aList.size() - 1) { dataItem = aList.get(index) Display dataItem } Access and Manipulation of ADT’s Data - displayList

replace(aList, i, newItem) if (i >= 0 and i < aList.size()) { aList.remove(i) aList.add(i, newItem) } Access and Manipulation of ADT’s Data - replace

Figure 3.6 The wall between displayList and the implementation of the ADT list

Make an appointment for a certain date, time, and purpose. Cancel the appointment for a certain date and time. Check whether you have an appointment at a given time and date. Determine the purpose of the appointment at a given time and date. ADT for appointment book

createAppointmentBook() isAppointment(date, time) makeAppointment(date, time, purpose) cancelAppointment(date, time) checkAppointment(date, time) More operations based on the operations above, e.g. change the date or time of a particular appointment within the existing appointment book. What needs to be done to achieve that? ADT appointment -Pseudocode

Get the purpose of the old appointment Check if the new date and time is available to appointment If yes, make the appointment at new date and time. If no, remind the user of the existing appointment and the failure to make the new appointment. ADT appointment -Pseudocode

Java Classes (class Sphere) Java Inheritance (class ColoredSphere) Java Interfaces Java Exceptions Implementing ADTs in Java

Figure 3.7 ADT operations provide access to a data structure

Figure 3.8 Violating the wall of ADT operations

Figure 3.9 An object’s data and methods are encapsulated

createList() isEmpty() size() add(newPosition, newItem) remove(index) removeAll() get(index, dataItem) An Array-Based Implementation of the ADT List

Figure 3.10 An array-based implementation of the ADT list

Figure 3.11 Shifting items for insertion at index 2

Figure 3.12 a) Deletion causes a gap; b) fill gap by shifting

Procedural abstraction Information hiding