JavaBeans

Question 1

What is component software?

Answer 1

Component software is software that is designed to work as a component of a larger application. Think of the way PCs are built: memory chips, CPUs, keyboards, etc.

Question 2

Why does component software work?

Answer 2

The interfaces between software components are standardized, so they work together seamlessly.

Question 3

How do components communicate with one another?

Answer 3

Through interfaces. The component offers services to the rest of the system. a provided interface specifies the services that other components can utilize, and how they can do so.

Question 4

Are components encapsulated? Why?

Answer 4

Yes. Other components do not need to know how the services are implemented, they just need to work.

Question 5

Describe the principle of substitutability with respect to component software.

Answer 5

A component should be able to replace another component if the successor component meets the requirements of the initial component (expressed via interfaces). This allows us to use updated versions or an alternative without breaking the system.

Question 6

Name two techniques for employing a component across network links

Answer 6

1. serialization

2. marshalling

Question 7

Compare and contrast object oriented programming and component-based software engineering.

Answer 7

OOP believes software should be modeled after the conceptual way we think about objects in the world and how they behave (mammal, dog, barks, etc).

Component-based software states that developers should construct software by gluing together prefabricated components– modularizing systems.

Question 8

Where is a discussion about component programming more relevant, java beans or enterprise java bean? Why?

Answer 8

Enterprise Java Bean (EJB). EJBs are distributed components. JavaBeans are local program components, usually GUI.

Question 9

What is the point of a JavaBean?

Answer 9

The primary intent of the JaveBean is to support visual application development environments (though the patterns defined by the javabean spec are applicable to class libraries in general).

By default, many java classes are beans simply because they follow javabean method-naming and event-handling conventions.

Question 10

What is a javabean usually?

Answer 10

A javabean is usually simply a class that subclasses java.awt.Component and implements object serialization eo externalization.

the javabean follows a standard set of method-naming conventions that allow application builder tools to automatically detect the properties, actions, and events support by a javabean through introspection.

Question 11

What is the purpose of an Enterprise Java Bean?

Answer 11

The purpose of an EJB is to isolate business logic and data access in server-side components.

They can also be accessed in visual development tools to link events (perhaps originating from a client javabean).

Question 12

JavaBean can be read as a synonym for what?

Answer 12

component

also, it’s pretty much just a java object. :/

Question 13

Where do javabeans typically run, client side or server side?

Answer 13

usually client.

Question 14

Enterprise java bean is typically for client or server side?

Answer 14

server side

Question 15

Which kind of classes is a javabeans component?

Answer 15

every java user interface class is a javabeans component

Question 16

what will learning javabeans help you do?

Answer 16

create custom events

develop your own source components that can fire events

Question 17

What are the minimum java bean requirements?

Answer 17

1. A bean must be a public class
2. A bean must have a no-arg constructor (though it can have others too)
3. A bean must implement the java.io.Serializable interface

Question 18

A javabean component is a special kind of java class. Sum it up in a sentence.

Answer 18

A javabean component is a serializable public class with a public no-arg constructor.

Question 19

Describe property naming patterns for javabeans

Answer 19

The javabean, like all classes, can have properties. Primitive type or an object type. The property type dictates the signature of the accessor and mutator methods.

public String getMessage()

public boolean isCentered()

Question 20

what do properties describe in the bean?

Answer 20

properties describe the state of the bean

Question 21

data fields are used to store properties. how do they work in beans?

Answer 21

a bean property is not necessarily a data field.

Question 22

what is the difference between a property and a field?

Answer 22

a property is a concept, a field is an implementation

Field: a data member of a class. unless specified otherwise, a field is not static.

Property: characteristics of an object that users can set, such as the color of a window.

A property may be read-only with a get method but not set method, or write-only with a set method but no get method

Question 23

Can beans communicate with other beans?

Answer 23

Yes.

Question 24

What model provides the foundation for communcation between beans?

Answer 24

The Java event delegation model enables beans to send, recieve, and handle events.

event object
source object
event listener object

–review event driven programming for more

This is called the “delegation model” because the source object delegates the event to the listeners for processing.

Question 25

What is an event source?

Answer 25

The component on which an event is generated.

Every java GUI component is an event source for one or more events.

A JButton object fires a java.awt.event.ActionEvent when it is clicked.

Question 26

what should a source component contain?

Answer 26

code that detects and external or internal action that triggers the event

the source should fire an event to the listeners by invoking the event handler defined by the listeners.

the source component must also contain methods for registered and deregistering listeners.

Question 27

what should a listener component do?

Answer 27

a listener component for an event must implement the event listener interface.

otherwise, the object of the listener component cannot receive event notifications from a source component.

Question 28

can a listener component have more than one listener interface?

Answer 28

yes. it may register many listeners. it may also register itself.

Question 29

what is the naming pattern for removing custom source component?

Answer 29

public void removeListener(Listener 1)

Question 30

what is the naming pattern for adding a unicast listener

Answer 30

public void addListener(Listener 1)

throws TooManyListenersException;

Question 31

what is the naming pattern for adding a multicast listener

Answer 31

public void addListener(Listener 1)

*no exception thrown, as in unicast listener

Question 32

Give an example of a custom source component

Answer 32

Course class, when number of students cap has been reached and we need to do something if the cap is exceeded.

Question 33

why does synchronizing certain methods help?

Answer 33

avoids data corruption (for example, when attempting to register multiple listeners concurrently)

Question 34

if you want to create a custom event class, what must you extend?

Answer 34

java.util.EventObject or a subclass that class

Question 35

a custom event listener interface must extend what class??

Answer 35

java.util.EventListener or a subinterface of that class

Question 36

by convention, a custom listener interface should be named what?

Answer 36

XListener for the event class named XEvent

Question 37

by convention, a custom event class should be named what?

Answer 37

XEvent

Question 38

why doesn’t a custom event class have a no arg constructor?

Answer 38

you must always specify a source for the event when creating an event

Question 39

what does unicasted mean?

Answer 39

only one listener object is notified of the event

Question 40

what does multicasted mean?

Answer 40

each object in a list of listeners is notified of the event

Question 41

what happens when a builder tool inspects a bean that includes:

public color getColor()
public void setColor(Color c)

Answer 41

• the tool infers that a property named color exists
• the builder tool knows this property is readable and writable
• the builder knows that the type is Color
• the builder can look for a property editor for the type, and display the property (usually in a property sheet) for editing

Question 42

what is an indexed property?

Answer 42

an indexed property is an ordered collection of values associated with a single name.

The individual values are accessed using an integer index (like an array).

Question 43

What design pattern must an indexed property follow?

Answer 43

Access entire array:

public [] get();

public void set()[] value);

Access individual values in the property array:

public [] get(int index);

public void set(int index, )[] value);

Question 44

what is a bound property?

Answer 44

a bound property notifies listeners when its value changes.

Question 45

What class must a bound property use?

Answer 45

PropertyChangeSupport

Question 46

What methods should a bounded property use?

Answer 46

addPropertyChangeListener

removePropertyChangeListener

Question 47

where does PropertyChangeSupport live?

Answer 47

java.beans package

Question 48

give an example of how you would use a bound property

Answer 48

number of tickets sold at a concert. we only have 1000 tickets. we can’t sell 1001, so we need to close sales when we hit 1000.

Question 49

describe what a bound property must do on a listener list

Answer 49

a bound property must be able to add and remove itself

Question 50

what is a constrained property

Answer 50

a constrained property is a special kind of bound property

the bean keeps track of a set of veto listeners

when a constrained property is about to change, the listeners are consulted. any one of the listeners has a chance to veto the change.

Question 51

what is a veto listener

Answer 51

a veto listener vetos a constrained property change when the property change asks the other listeners if it should change

Question 52

are veto listeners part of the property change listeners?

Answer 52

no. they are in the class VetoableChangeSupport

Question 53

where does a veto change live?

Answer 53

VetoableChangeSupport