IT 206 Quiz 2 Study Guide & Final Review

What is an association relationship?

"Uses" relationship Represents a conceptual relationship, where there is NO owner Both classes can exist independently Classes can be accessed directly Student uses a library

What is a composition relationship?

"has a" "death" relationship Special form of association (strong-type) where two class are connected together conceptually with ownership Represents a "death" relationship, with one class owning another. If parent class dies so does the child. Classes are existent-dependent Child class can only be accessed via parent clas Employee has a job course has an instructor

What is an aggregation relationship?

"has a" relationship Special form of association (weak-type) Represents a conceptual relationship, where there is one owner Both classes can exist independently Child class can be accessed directly course has an instructor

What is a Class?

A blueprint or template that defines the attributes & behaviors that an object of that class can have. Attributes in a class can be of mix data types. (both primitive and reference)

What is a concrete class?

A class that can be instantiated

What is an abstract class?

A class that is used when it is desirable to force a class to be extended because it is too broad or "abstract" to be instantiated on its own. Cannot instantiate objects from an abstract class Classes should have at least one abstract method

What is an abstract method?

A method that must be overridden at some point Has no method body

What happens when you call and override a method by a subclass object?

A new method is invoked with the same method name

How to prevent from violation information hiding with arrays of instance variables?

All constructors that accept an array as a parameter for an array as an instance variable should use a copy of the array and not a reference value to the array All accessor methods that access an array as an instance variable should return a copy of the array and not a reference value to the array Similar to accessors, all mutator methods that accept an array as a parameter for an array as an instance variable should use a copy of the array to store values and not the original array

Method Overriding

Allows you to reuse methods in the subclass from the superclass. These methods can be enhanced (more specialized). They must have the same method declaration (same name & formal parameters) in the subclass that is in the superclass. Ex// toString()

What is an Object?

An object represents a specific instance of a class. Each object has the same attributes but with unique values. All objects contain the same behaviors

What is a stream?

An object that manages data flow between the program and I/O devieces or files

How do owner (parent) classes incorporate child classes?

As instance variables

How many constructors will be invoked when a subclass object is instantiated (created)?

At least two constructors are invoked, the subclass constructor that invokes the superclass constructor. A superclass constructor must have a default constructor if there are no specific constructors which in turn must be called when a sublcass object is created.

Where in the class is the space in memory allocated for the Array of Instance Variables?

At object creation time, so within the constructor

How will can you make sure a text file is saved?

By making sure you explicitly close the output stream If you don't explicitly close it, Java will close it for you when program ends Best Practice: Make sure you explicitly close the file

You ______ instantiate an object of an abstract class

Cannot

Instance variables in inheritance

Cannot be overridden, only non-private variables are inherited.

What is downcasting?

Casting an object of a subclass that has a superclass reference value to a subclass reference value

What is upcasting?

Casting an object of subclass that has subclass reference value to a superclass reference value such as for storing objects into an array Cast operator is NOT needed because of substitution principle (JAVA will do this for you)

FileNotFound is a _____ exception

Checked

What is an interface?

Collection of abstract methods and constants These abstract methods are common methods that may be implemented by several disparate classes. Interface is like a fake inheritance Provides for consistency of activity across disparate classes Behaviors are done differently in each class. Ex// getMeasure()

Text files are...

Commonly used to store data Both numbers and words can be stored as text

When down casting, a ______ results in cast attempts that are not possible - where objects are not related

Compiler Error

What are the steps of adding a value to an array as an instance variable?

Create a mutator method that accepts a value Check if there is room in the instance array Check if the parameter value is valid Set the parameter value to the array Increment the current size

What are the steps of accessing a specific element in an array as an instance variable?

Create an accessor method that accepts an index parameter and has return type Check to make sure that the index is valid. Return the element at the specified index

What are the steps when writing to a file?

Create an object of the PrintWriter class that takes in an object of the FileOutputStream class which takes in an object of the File class 1: Pass the name of the file in code 2. Ask the user to specify the file name 3. Allow the user to select a file PrintWriter may throw a checked FileNotFoundException In this case, FileNotFound does not mean the file was not found. It means the file could not be created. As a result, the method must "catch or declare" the exception

What are the 2 types of levels in the inheritance hierarchy?

Direct superclass/subclass: one level ex// car is a vehicle Indirect superclass/subclass: two or more levels ex// sports is a car, car is a vehicle

PrinterWriter

Does the writing

When using string literals to specify file paths, what should be used?

Double backslashes, since on backslash is an escape character

What is it called when the JVM determines which method to select?

Dynamic binding

What is single inheritance?

Each subclass has only one superclass Java supports only single inheritance

What are the advantages of OO?

Easier to reuse code/easier maintenance Easier to increase an application's functionality Information Hiding - protect the data Data Encapsulation (Requirement of OO)

How are interfaces different from class?

Every method in an interface is abstract Every method in an interface is public There are no instance variables There are no static methods in interfaces

What are checked exceptions?

Exceptions represent invalid conditions outside immediate control of program Exceptions of the Exceptions class are checked Methods are obliged to establish a policy for handling them (catch or declare) IOexception, FileNotFound

What are unchecked exceptions?

Exceptions that are defects in the program (programmer error in logic) RunTimeExceptions are unchecked Not obligated to establish a policy for handling them DivisionByZero, runtime errors

What is a common error when implementing an interface?

Forgetting to declare the overridden method public in the class that is doing the implementing.

How should exceptions be ordered?

From most specific to least specific NumberFormatException IllegalArgumentException Exception

JFileChooser

GUI presented to user to select a file

The inheritance hierarchy becomes more____as you go up the chart

Generalized

When to use an abstract class instead of an interface?

Generally if the classes have an inheritance relationship, use an abstract class.

Association multiplicity

Goes both ways

Substitution Principle

In inheritance, a sublcass object reference value may be used in any location that expects a superclass object reference value

What are the 4 types of relationships?

Inheritance Association Aggregation Composition

Data flow IN

Input stream From JOP.showInputDialog and/or taken from file

What is the issue with information hiding and Array of Instance Variables?

Instance variable are meant to be private should be accessed and manipulated from the data definition class. Instance variables also store the reference value that points to the contents of an array. Within that array are the set of instance variables. The issues lies when it comes time to sharing the contents. Since it's an array, the contents aren't passed, only the reference value. This creates a backdoor for an external class (implementation) to be able to read/update the contents of the array directly instead of using methods in the data definition class.

How is an Array of Instance Variables created?

Instantiated using the "new" keyword

What is Inheritance?

It is conceptualized as a hierarchy where a subclass inherits properties (attributes) and behaviors from a superclass "is-a" relationship Provides easier maintenance and less duplication than maintaining individual classes Some type of Generalization/specialization hierarchy

What is instanceof?

It is used to perform safe downcasting to prevent syntax errors such as ClassCastException if (v instanceof Car) { Car c = (Car)v; c.getIsSport(); } OR if (v instanceof Car) { ((Car)v).getIsSport(); }

What is said about when a class implements an interface?

It must override all the methods of that interface since all interface methods are abstract

What is dynamic binding?

Just means that calls to overridden methods are determined at execution time (based on object type not reference) need superlass reference and overridden methods

Instances of Association are called

Links

Java is a strongly typed language

Meaning variables must be declared with data types

______ is when two methods share the same name but different parameters

Method overloading

______ is when two methods share the same name and parameters, but have different implementation

Method overriding

What are the disadvantages of OO?

More time consuming than procedural

How many catch blocks can be used for one try?

Multiple

What is OO programming?

Object-Oriented programming is modeled on the concept of real world "things" (objects) and their interactions (relationships) with other "things". Objects are based off real world "things", with attributes and behaviors OO still relates to the procedural approach like breaking tasks into sub tasks and reusing methods to handle those tasks.

When to use inheritance?

Only when the classes differ in both multiple attributes and behaviors

Data flow OUT

Output String From JOP.showMessageDialog and/or provided from a file

We are able to have an superclass object reference assigned to a sublcass object that is derived from that superclass because of

Polymorphism

What is polymorphism?

Polymorphism refers to the fact that you can have different subclass with the reference value of a single superclass and be able to select proper methods (that are in both the super and subclass) based on the subclass object type

3 types of methods that cannot be overridden

Private methods - meant to be private and not inherited (password validation) Static methods - apply for all instances Final methods - cannot be changed

What are exceptions?

Rare events outside normal behavior of code

Where in the class is the Array of Instance Variables declared?

Reference value for the array is declared at the top of the class

Overridden methods in a subclass cannot be more ______ than the method in the super class

Restrictive

FileOutputStream

Sends the data

What is the power of inheritance?

Software reusability New classes created (extended) from existing class use existing class' properties and behaviors (no need to code again) Subclasses: Are enhanced with additional capabilities (more specialized) Inherited behaviors can be customized New properties and behaviors can be added

The inheritance hierarchy becomes more______as you go down the chart

Specialized

What are not inherited?

Static methods & Constructors Constructors are not members of a class

Give an example of a "is a" relationship

Student is a Person

Most "portable" type of data file

Text file

Text files vs Binary files

Text files are Sequence of characters when view by text editor or read by program Designed to be read by humans Binary files' contents are handled as sequences of binary digits Designed to be read only by programs

What must be abstract in order for a method to be abstract?

The class must be abstract as well

What is the equals method?

The equals method is a method from the object class that is used to compare two objects to each other. public boolean equals(Object o) { if (o == null || this.getClass() != o.getClass()) { return false; } //downcast Student s = (Student)o; return this.getName().equals(s.getName()) && this.getGPA() == s.getGPA();

What is the Object Class?

The highest class in the OO hierarchy. All classes extend the Object class. Common overridden methods include toString() and equals(object o)

How are copy constructors used?

They are used when accessing or mutating the object instance variable within the parent class. Like arrays, the object reference value is stored into the instance variable, so to avoid violating information hiding , a reference value of a copied instance object is used. Accessor - return a copy of the object Mutator - set a copy of the object

What does throw early/catch late mean

Throw early means that a method detects a problem it can't solve, it is better to throw (address/state/inform) an exception rather than to come up with a work aorund Catch late means that a method should only catch an exception if it can remedy the error, if it cannot, it should propagate (send) it to the calling method until it has reached a method suitable to address the error.

Why would you need to downcast?

To call methods that only exist in the subclass

All methods in interfaces are public and abstract

True

An abstract class must be extended in order to be instantiated

True

If a class has an abstract method, then the class is also abstract

True

The "public abstract" keywords do not need to be provided in interfaces

True

How can you append to a file?

Use println

How do you use an interface with a class?

Use the "implements" keyword

How to call an overridden method from the super class?

Use the "super" keyword

What is a copy constructor?

Used to create a copy of an object and its attributes

Scanner Cass

Used to read text from a file

How to access instance variables?

Via accessors and mutators

What is static binding?

When the compile knows which method to use

When to use an interface instead of an abstract class?

When you need to force the creation of similar behaviors across disparate classes

When importing classes to read/write a file you can import all the classes or just the following specific ones

Writing import java.io.File; import java.io.FileNotFoundException; import java.io.PrintWriter; import javax.swing.JFileChooser; Read import java.util.Scanner; import javax.swing.JFileChooser; A shortcut can be used to reference all files in the package, such as: import java.io.*;

Can a class implement more than one interface?

Yes

Are interfaces abstract?

Yes (since it has abstract methods, the class must be abstract as well)

What will happen if the file name doesnt exist?

a new empty file with a name will be created

How do you create a custom checked exception?

create a class that extends the Exception class

How do you create a custom unchecked exception?

create a class that extends the RuntimeException class

How are constants written in interfaces?

double speed = 45.5; String message = "Hello"; int distance = 10;

What are the methods to write to a file?

print - Prints out a message println -Prints out a message followed by a new line printf -Prints out a formatted message. Some examples: %d - Print the next item as an integer (int) %f - Print the next item as a real number (double)

What will happen if the file name already exists?

the old contents of the file will be lost (overwritten)