Chapter 4: Classes & Objects, Object Oriented Data Structures Java: Chapter 2, Java Methods Chapter 1

What is an object?

An entity that models something from the real world.

What three things can an object represent?

GUI components ( title bar, buttons), software entities ( events, files), abstract concepts ( location on grid, game rules)

An object is an ________ of its class.

instance

What is the creation of an object called?

An Instantiation (of its class)

Where does the object's memory go when it is no longer being used?

The garbage collection (free-memory pool)

What is called upon to create an object?

The new operator calls the constructor

What must the name of the constructor be?

The name of the constructor must be the same name of its class:

public balloon ( int x, int y)

What are the restrictions for constructors and its parameters?

Constructors can have args or many args. However, constructors with the same number and type of parameters cannot coexist.

What does void indicate?

Method does not return any value.

What is the difference between public and private methods?

Private methods can only be called from constructors or methods of the same class while public methods can be called from other classes as well.

What methods give outsiders access to public and private methods?

Accessors and getters

What type of relationship exists between a RoundBalloon and a Balloon?

A RoundBalloon IS-A Balloon.

Balloon b1 = new RoundBalloon();

RoundBalloon b2 = new RoundBalloon(10, 20, color.RED);

What does "jar" stand for?

Java archive

What does a jar file allow you to do?

allows you to run a Java program with a simple click, w/o creating any projects in an IDE (no need for NetBeans!); same as .zip file

What are two advantages of encapsulation/information hiding?

-Change the structure of fields and rest of project won't be affected;

-easier to maintain, document, and reuse encapsulated class;

-other classes do not need to know the implementation details to use the class effectively

What is a class?

A class (class definition) is a blueprint for making an object.

Where is the source code for a class usually stored?

In a separate file with the same name as the class with extension ".java" (Balloon class in Balloon.java); capitalized by convention

What is a wrapper class?

These classes (Integer, Long, Byte) "wrap" primitive data types (int, long, byte) into an object. Numbers and characters are not objects.

What three things will a class always describe of an object?

The instance variables/fields (attributes), the procedures for creating the object (constructors), and the behaviors of the object (methods)

What does CRC stand for?

Class, Responsibilities, and Collaborators (classes that are used by this class - Balloon class uses Canvas class)

What is the main method?

The place where control is passed when the Java program starts. There can only be one public main method

What class extends what other class?

Subclass extends Superclass

How many classes can can extend the same superclass? How many superclasses can a single subclass extend?

Several classes can extend the same superclass, but a subclass can extend only one superclass (no multiple inheritance).

What does and doesn't a subclass inherit?

A subclass inherits all the methods and fields of its superclass, but not the constructors.

What is the paradox of subclass inheritance?

A subclass inherits the private fields of its superclass but does not have access to them.

What are two attributes that a field always has?

Data type (int, double, String, Color) & name (usually lowercase by convention)

Why are fields usually private?

So that a programmer can change the number, names, and types of fields without affecting other classes of the same project

Give an example and a diagram of a HAS-A relationship.

Balloon <>------------Color

(Balloon has a color)

What does static mean?

The field belongs to all objects of the class, not to a particular class. (static applies to methods too)

What does final mean?

Means the field is constant (values cannot be changed)

What is java.util?

Miscellaneous utility classes

What is java.awt?

Windowing and graphics toolkit

What is javax.swing?

GUI development package

What is an import statement?

Statements that allow us to use short names for library classes instead of fully-qualified names (Ex: Whenever you see JButton, treat it as javax.swing.JButton)

What does the . (java.awt.) wildcard symbol mean?

Imports all the classes from that package

Abstraction

A model of a system that includes only the details essential to the perspective of the viewer of the system

Information hiding

The practice of hiding details within a module with the goal of controlling access to the details from the rest of the system

Data abstraction

The separation of a data type's logical properties from its implementation

Abstract data type (ADT)

A data type whose properties (domain and operations) are specified independently of any particular implementation

Application (or user or client) level

We use the ADT to solve a problem. When working at this level we only need to know how to create instances of the ADT and invoke its operations.

Logical (or abstract) level

Provides an abstract view of the data values (the domain) and the set of operations to manipulate them. At this level, we deal with the "what" questions. What is the ADT? What does it model? What are its responsibilities? What is its interface?

Implementation (or concrete) level

Provides a specific representation of the structure to hold the data and the implementation of the operations. Here we deal with the "how" questions.

Preconditions

Assumptions that must be true on entry into a method for it to work correctly.

Postconditions or Effects

The results expected at the exit of a method, assuming that the preconditions are true.

Abstract Method Rules

Only includes a Description of its parameters

No method bodies or implementations are allowed

Only the interface of the method is included.

How are Java interfaces similar to Java classes?

- Can include variable declarations

- Can include methods

What conditions do Java interfaces have?

- Variables must be constant

- Methods must be abstract

- A Java interface cannot be instantiated

Why would we use an interface to formally specify the logical level of an ADT?

- It provides a template for classes to fill

- A separate class then "implements" it

What are some benefits to using an interface

- We can check if our syntax meets our specifications

- We can check if the interface "contract is met", IE: method names, return types, and parameters are correct.

- We can provide a consistent interface to applications from among alternate implementations of the ADT.

What are the responsibilities of StringLog ADT

Remember the strings that have been inserted into it and to verify if their are any matching strings

What is a StringLog used for?

To record strings and later check to see if a particular string has been recorded

What must a StringLog have?

A "Name"

Constructors

Crates a new instance of the ADT. It's up to the implementer of the StringLog to decide how many and what kind of constructor to provide.

Types of Transformers & definitions

- Insert(String Element): Assumes the StringLog is not full and adds elements to the log of strings

- Clear: resets the StringLog to the empty state; the StringLog retains its name.

Types of Observers

- contains(String element): returns true if element is in the StringLog, false otherwise; We ignore case when comparing the strings.

- size: returns the number of elements currently held in the StringLog.

- isFull: returns whether or not the StringLog is full.

- getName: returns the name attribute of the StringLog.

- toString: returns a nicely formatted string that represents the entire contents of the StringLog.

Application (or user or client) level

The UseStringLog program is the application. It declares a variable log of type StringLogInterface. It uses the ArrayStringLog implementation of the StringLogInterface to perform some simple tasks.

Logical (or abstract) level

StringLogInterface provides an abstract view of the StringLog ADT. It is used by the UseStringLog application and implemented by the ArrayStringLog class.

Implementation (or concrete) level

The ArrayStringLog class developed in Section 2.3 provides a specific implementation of the StringLog ADT, fulfilling the contract presented by the StringLogInterface. It is used by applications such as UseStringLog. Likewise, the LinkedStringLog class (see Section 2.6) also provides an implementation.

Instance variable

String[] log;

The elements of a StringLog are stored in an array of String objects named log.

Instance variable

int lastIndex = -1;

Originally the array is empty. Each time the insert command is invoked another string is added to the array. We use this variable to track the index of the "last" string inserted into the array.

Instance variable

String name;

Recall that every StringLog must have a name. We call the needed variable name.

Stepwise Refinement

- Approach a problem in stages.

- Similar steps are followed during each stage, with the only difference being the level of detail involved.

-The completion of each stage brings us closer to solving our problem.

What are the Two Standard variations of stepwise refinement

- Top-Down: the problem is broken down into several parts and each part is divided and then those parts are subdivided. Used to design non-trivial methods

- Bottom-up: Details come first. They are brought together into increasingly higher-level components. A useful approach if you can identify previously created program components to reuse in creating your system.

What are the two ways to define software testing?

- The process of executing a program with data sets designed to discover errors.

- Software testing is one facet of software verification.

Software validation

The process of determining the degree to which software fulfills its intended purpose.

Software verification

The process of determining the degree to which a software product fulfills its specifications

Deskchecking

Tracing an execution of a design or program on paper

Walk-through

A verification method in which a team performs a manual simulation of the program or design

Inspection

A verification method in which one member of a team reads the program or design line by line and the others point out errors

What purpose do test cases serve?

allow us to assert that a program works correctly

What must we do for each test case?

-determine inputs that represent the test case

-determine the expected behavior of the program for the given input

-run the program and observe the resulting behavior

-compare the expected behavior and the actual behavior of the program

Functional domain

The set of valid input data for a program or method

In limited test cases, where the functional domain is small, what can someone do to verify the program is working?

Test the program against every possible input element.

How to identify text cases?

- Covers general dimensions of data

- Within each dimension identify categories of inputs and expected results

- Test at least one instance of each combination of categories across dimensions.

- Testing like this is called black-box testing and the tester must know the external interface to the module.

Test plan

A document showing the test cases planned for a program or module, their purposes, inputs, expected outputs, and criteria for success

Test driver

A program that calls operations exported from a class, allowing us to test the results of the operations

What is a node?

A node in a linked list is an object that holds some important information, such as a string, plus a link to the exact same type of object, i.e. to an object of the same class.

Self-referential class

A class that includes an instance variable or variables that can hold a reference to an object of the same class

LLStringNode log

In this implementation, the elements of a StringLog are stored in a linked list of LLStringNode objects. We call the instance variable that we use to access the strings log. It will reference the first node on the linked list, so it is a reference to an object of the class LLStringNode.

String name;

Recall that every StringLog must have a name. We call the needed variable name.

central processing unit

CPU (acronym)

millions of semiconductor devices (transistors) etched into a silicon chip; speed measured in Hz

CPU (def)

combination of transistors into logical devices

gates (def)

random access memory

RAM (acronym)

CPU can read directly from and write to any memory location; holds data and CPU instructions

RAM (def)

read only memory

ROM (acronym)

initialization and hardware diagnostic programs; can never be deleted or edited

ROM (def)

secondary storage, input/ output

peripheral devices (ex)

1024

1KB= __ bytes

1024^2

1MB= __ bytes

1024^3

1GB= __ bytes

1024

1 terabyte= __ gigabytes

hard disk, CD-ROM, optical (ZIP) disk, memory stick/ flash drive

secondary storage (ex)

Input/ Output

I/O devices (acronym)

monitor and video adapter, keyboard, mouse, touchpad, internet adapter, modem, D/A and A/D convertors, scanners, digital cameras, printers

I/O devices (ex)

applications -> operating system -> device drivers -> BIOS, firmware

software layers order

program that maintains file system, dispatches applications, other system-level services

operating system (def)

program with simple text user interface

console application (def)

Graphical User Interface

GUI (acronym)

graphics, menus, buttons, icons

GUI (def)