Intermediate Java Exam 2

Front 1

Selection sort

Back 1

Algorithm that finds the smallest Item and put it into location 0, then finds the next smallest and places it into the 1 index. and so forth

Front 2

Inner Class

Back 2

a class that is declared within another class

Front 3

Every Java object has a pseudo-instance variable called ______ which is a refrence back to that same object

Back 3

.this

Front 4

______ implicitly converts back and forth between primitive types and there _______ classes.

Back 4

Autoboxing, Wrapper classes

Front 5

If JButton is clicked a ___________ is generated which then passed to a ____________ is linked to the JButton

Back 5

Action Event and Action Listener

Front 6

Name the layout managers in Java

Back 6

Flow Layout, GridLayout, BorderLayout, GridbagLayout

Front 7

Shallow Copy

Back 7

if a copy constuctor for a class makes a bitwise copy of all of the instance variables it is making a Shallow copy

Front 8

Binary Sort and its Function

Back 8

the amount of guesses it will take to find the value (Worst Case Scenario) is : logBase2(N) (Log N)

where N is the number of Items.

for this code to work the Array must be sorted in from Least to Great or Vice Verse.

The Code find the middle and compares that value. so if it is greater it will never search less.

Front 9

We can arrange graphical components differently in different parts of our JFrame by putting them into ____ objects, since each ________ has its own Layout Manager

Back 9

JPanel, JPanel

Front 10

T/F

The binary The binary search
algorithm requires the array being searched to be sorted.

Back 10

TRUE

Front 11

row major order

Back 11

The first index gives us a "row", which is an array of items

Front 12

data abstraction

Back 12

We don’t need to know the internal data representation
We don’t need to know the method implementation

Front 13

how the ArrayList is implemented

Back 13

Data is maintained in two parts:
an array to actually store the information
an int to keep track of the number of elements being stored

Front 14

Most of our operations are concerned with the logical size of the array

Back 14

Number of actual elements being stored

Front 15

The physical size of the array is

Back 15

abstracted out of our view

Front 16

The physical size of the array is abstracted out of our view meaning......

Back 16

This changes as necessary but we never need to know what it actually is in order to use the ArrayList
Remember previous discussion on resizing

Front 17

A is sorted in ascending order if

Back 17

A[i] < A[j] for all i < j

Front 18

A is sorted in descending order if

Back 18

A[i] > A[j] for all i < j

Front 19

Some algorithms are better than others
The most useful measure of “better” here

Back 19

is how long it takes to run
The better algorithms run a lot more quickly than the poorer algorithms

Front 20

SelectionSort

Back 20

SelectionSort is very intuitive:
Find the smallest item and swap it into index 0
Find the next smallest item and swap it into index 1
Find the next smallest item and swap it into index 2…
Find the next smallest item and swap it into index N-2

Front 21

InsertionSort

Back 21

unlike the other sorts, passes through the array only once. The insertion sort is commonly compared to organizing a handful of playing cards. You pick up the random cards one at a time. As you pick up each card, you insert it into its correct position in your hand of organized cards.

Front 22

Sequential Search

Back 22

Start at the beginning of the array and check each item in sequence until the end of the array is reached or the item is found

One stops the loop with failure (get to end)
The other stops the loop with success
If the data is unsorted, we cant do any better

Front 23

linear run-time

Back 23

time proportional to N, the number of items in the array

Front 24

Idea of Binary Search:

Back 24

Searching for a given key, K
Guess middle item, A[mid] in array
If A[mid] == K, we found it and are done
If A[mid] < K then K must be on right side of the array. If A[mid] > K then K must be on left side of the array. Either way, we eliminate ~1/2 of the remaining items with one guess

Front 25

associated with the class itself rather than individual objects.Can be accessed through the class using ClassName.variableName or through the objects using variableName from within an object objectName.variableName from outside an object. access from class or frm outsde of object,data must be public.

Back 25

Static Variables

Front 26

When should I use a variable and when should I use a method?

Back 26

Variables should be used to store the basic properties of an object
Can be changed through mutators but should not become "obsolete."Methods should be used to calculate / determine values using variables. We don't want to waste time calculating something that is set. However, if a value may change over time, it should be calc'ed

Front 27

Copying objects

Back 27

In Java there are two primary ways of doing this:
Using a “copy constructor” for the class

Using the “clone” method for a class

Front 28

copy constructor

Back 28

This method takes an argument of the same class type and makes a copy of the object
Ex: String newString = new String(oldString);

Front 29

“clone” method

Back 29

This allows an object to “make a copy of itself.”

defer it to CS 0445

Front 30

Assign each instance variable in the old object to the corresponding instance variable in the new object
If the instance variables are themselves references to objects, those objects will be shared
See ex12b.java and Scores.java

Back 30

Shallow Copy

Front 31

Copy primitive types normally
For reference types, do not assign the reference; rather “follow the reference” and copy that object as well
Note that this process could proceed through many levels
See ex12b.java and Scores.java

Back 31

Deep Copy

Front 32

Often in instance methods you are accessing both instance variables and method variables
If a method variable has the same name as an instance variable, updates will change the method variable, NOT the instance variable.

It allows disambiguation between instance variables and method variables

Back 32

The this. reference

Front 33

When a reference to an object is reassigned, the original object can no longer be accessed through that reference
If there is no other reference to that object, then it cannot be accessed, period
In this case the object has become ...

Back 33

Garbage Collection

Front 34

Graphical output and use of a mouse and other graphical components for input

Back 34

Graphical interfaces

Front 35

The AWT

Back 35

(Abstract Windowing Toolkit)

first versions of Java
Created components such as Frame, Panel, Button, TextField, Label
AWT varied on different windowing systems
AWT Java program looks different when run on MS Windows machines, MACs and Sun
because the differ underlying windowing systm

Front 36

more consistent in its look and feel across all platforms.

It also adds some extra features that did not exist in the AWT
components are similar to AWT in name, but with a “J” in front
Ex: JFrame, JPanel, JButton, JTextField, JLabel

Back 36

Swing

Front 37

Set of graphics and media packages that enables developers to design, create, test, debug and deploy rich client applications that operate consistently across diverse platforms

Back 37

JavaFX

Front 38

objects that will be the windows in graphical applications
We can draw/paint graphics within them

Back 38

JFrames

Front 39

bjects that will be the windows in graphical applications within the context of another program (i.e. a Web browser)

Back 39

JApplets

Front 40

simple components to show formatted text on the display
We can set the font type, size and color
We can set and change the text itself as desired throughout program execution

Back 40

JLabels

Front 41

simple components that can also show text on the display in addition
they also respond to clicks of the mouse

Back 41

JButtons

Front 42

If a user clicks the mouse within a JButton, an _______ object is generated in response
This object is passed automatically to an________
object

Back 42

ActionEvent, ActionListener

Front 43

The ActionListener must be registered to _______ to the JButton

Back 43

listen

Front 44

ActionListener is actually an

Back 44

interface with the single method actionPerformed().

Any class that implements actionPerformed() can be an ActionListener

like ControlListener you used in Assig4

causing the actionPerformed method within the ActionListener to execute

Front 45

It is the actionPerformed method that is doing the actual response to the button click
This idea is called

Back 45

event-driven programming

Programmer writes code to respond to the various events that may occur

Front 46

The basic idea for the different types of events...

Back 46

Triggered object generates an event object
Event object is passed to event listener object
Method in the event listener executes to handle the event
It is important that event handlers are linked to the appropriate event generators
Otherwise event will still be generated but will not be responded to

Front 47

If we want to have multiple components, we need to determine how to lay them out
To do this we use a_______

These determine how components appear in a window and how much space is allocated for them.

Back 47

layout manager

Front 48

Places components as we read a book – left to right top to bottom

Back 48

FlowLayout

Front 49

Places components in an equally sized 2-dimensional rectangular grid

Back 49

GridLayout

Front 50

This is a component in which the user can enter text

Back 50

JTextField

Front 51

Have most of the functionality of JFrames, except without the title/menu bar
Can store other components and lay them out using a layout manager

Back 51

JPanels

Front 52

subdivides our window into 5 areas
NORTH, SOUTH, EAST, WEST, CENTER
We can put a component in each area or just some of them
If the component is a JPanel, we can then put our other components within that

Back 52

BorderLayout

Front 53

How to terminate a graphical program?

Back 53

set an option in the JFrame
theWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

or create a JButton that uses the System.exit(0); method call

Front 54

What if we want it to also store and manipulate our own data in the JPanel?

Back 54

We need to extend it using inheritance

Front 55

When we extend a class in Java, the new class has ...

Back 55

all of the functionality of the original, plus any new functionality that we give it via additional instance variables and methods
So, we can do this:
class MyPanel extends JPanel
We can then put whatever we’d like into our new class.We can add new instance variables, methods or both

Front 56

(T/F) ActionListener is a class

Back 56

false. ActionListener is an interface

Front 57

A _____ is a named set of methods.

Back 57

Java interface

Front 58

(T/F) A Java interface is a named set of methods
headers and method bodies.

Back 58

False, A Java interface is a named set of methods
However, no method bodies are given – just the headers

Front 59

In Java interface: Static constants (are allowed/not allowed),

instance variables (are allowed/not allowed), static methods (are allowed/not allowed).

Back 59

Static constants are ALLOWED

Instance variables are NOT Allowed
Static methods are NOT Allowed

Front 60

(T/F) Any Java class (no matter what its inheritance) can implement an interface by implementing the methods defined in it.

Back 60

True. Essentially an interface is stating an ABILITY of the class

Front 61

(T/F) A given class can implement any number of interfaces

Back 61

True

Front 62

Note that in the________we must declare that the interfaces are implemented

Back 62

Class header

Front 63

can be used to reference any object that implements that interface

Back 63

interface variable

Front 64

(T/F) a single class may implement many interfaces, if it is being
accessed through an interface variable, the methods in the other interfaces are
also available.

Back 64

False! if accessed through an interface variable, the methods in the other interfaces are
NOT available. The interface masks the object such that only the interface methods are visible / callable. If other methods are attempted to be accessed, a compilation error will result.

But only the interface methods are accessible through the interface reference

Front 65

Even though a single class may implement many interfaces, if it is being accessed through an interface variable, the methods in the other interfaces are not available. Describe the example used in class. Booable();

Back 65

Laughable L1, L2, L3;
L1 = new Comedian();
L2 = new SitCom(); // implements Laughable
L3 = new Clown(); // implements Laughable
L1.laugh(); L2.laugh(); L3.laugh();
L1.boo(); // illegal evn thoComedian has boo()
((Booable)L1).boo(); // this is ok since we cast

Front 66

________ are classes that ______ objects around primitive values, thus making them compatible with other Java classes.

Back 66

Wrappers, "Wrap"

Front 67

Java primitive types are NOT classes, and thus cannot be used in this way.
If I make an array of Object or any other class, primitive types cannot be stored in it. How do we work around this problem?

Back 67

by using Wrapper Classes

Front 68

a static method that enables us to

convert from a String into an int.

Back 68

Integer.parseInt()

Front 69

a static method that tests if a letter is a character or not.

Back 69

Character.isLetter()

Front 70

(T/F) Arithmetic operations are defined for wrapper classes.

Back 70

FALSE! Arithmetic operations are NOT defined for wrapper classes. We need to get the underlying primitive.

k = i + j;

k = new Integer(i.intValue() + j.intValue());

In words: Get the primitive value of each Integer object, add them, then create a new Integer object with the result

Front 71

This does the conversion back and forth automatically.

Back 71

Autoboxing

Front 72

(T/F) autoboxing Saves the programmer some keystrokes and improves efficiency.

Back 72

FALSE! Saves the programmer some keystrokes
However, the work STILL IS DONE, so from an efficiency point of view we are not saving
Should not use unless absolutely needed

Front 73

One ability of the wrapper classes is....

Back 73

static methods to parse strings into the correct primitive values

Integer.parseInt(), Double.parseDouble(), Boolean.parseBoolean()

These enable us to read data in as Strings, then convert to the appropriate primitive type afterward

Front 74

The Character wrapper class provides many useful methods:

Back 74

Case conversion, checking for letters, checking for digits.

Can be useful when we are parsing text files ourselves.

Front 75

The String class has some very useful methods:

Back 75

ex:

split()

See ex18.java

Front 76

Sometimes we want to build a new class that is largely like one we already have
Much of the functionality we need is already there, but some things need to be added or changed. We can achieve this by...

Back 76

using inheritance! wahhhhh !

Attributes of a base class, or superclass are passed on to a subclass

Front 77

the “is a” idea

Back 77

A subclass object “is a” superclass object.

Note that “is a” is a one way operation

Front 78

“Is a” is a ____ way relationship.

Back 78

“Is a” is a one way relationship.

Front 79

Inheritance in Java is implemented by ______a class

Back 79

Inheritance in Java is implemented by extending a class.

We saw this already in Counters2.java, where our new class extended JPanel

Front 80

The protected declaration is...

Back 80

...between public and private.

Protected data and methods are directly accessible in the base class and in any subclasses (and in the current package).

However, they are NOT directly accessible anywhere else

Front 81

In Java, class _______is the base class to all other classes.

Back 81

In Java, class Object is the base class to all other classes

Front 82

The tree of classes that extend from Object and all of its subclasses is called...

Back 82

...the class hierarchy

Front 83

All classes eventually lead back up to....

Back 83

All classes eventually lead back up to Object

Front 84

class hierarchy enables...

Back 84

enables consistent access of objects of different classes, as we shall see shortly

Front 85

it allows us to mix methods and objects of different types in a consistent way.

Back 85

polymorphism

Front 86

method overloading is also called...

Back 86

ad hoc polymorphism

Front 87

ad hoc polymorphism is also called ...

Back 87

method overloading

Front 88

ad hoc polymorphism, or method overloading

Back 88

In this case different methods within the same class or in a common hierarchy share the same name, but have different method signatures (name + parameters)

public static float max(float a, float b)
public static float max(float a, float b, float c)
public static int max(int a, int b)

Front 89

When a method is called, the call signature is matched to the correct method version. When is this done?

Back 89

This is done during program COMPILATION

Front 90

ad hoc polymorph, or method overloading, If an exact signature match is not possible, it will select the next closest via ...

Back 90

via “widening” of the values is used

Front 91

when values of “smaller” types are cast into values of “larger” types, this is called...

hint: polymorph concept

Back 91

Widening.

Fewer widenings provides a "closer" match

Front 92

If two or more versions of the method are possible with the same amount of “widening”, the call is _________, and a ______ error will result.

Back 92

If two or more versions of the method are possible with the same amount of “widening”, the call is ambiguous, and a compilation error will result

Front 93

Subclassing Polymorphism
Sometimes called...

Back 93

“true polymorphism”

Front 94

Subclassing Polymorphism

Consists basically of two ideas:

Back 94

Method overriding
Dynamic (or late) binding

Front 95

Method overriding

Back 95

A method defined in a superclass is redefined in a subclass with an identical method signature
Since the signatures are identical, rather than overloading the method, it is instead overriding the method
For subclass objects, the definition in the subclass replaces the version in the superclass

Front 96

Dynamic (or late) binding

Back 96

The code executed for a method call is associated with the call during run-time
The actual method executed is determined by the type of the object, not the type of the reference

Front 97

Polymorphism example: the Animals

Back 97

Animal [] A = new Animal[3];
A[0] = new Bird();
A[1] = new Person();
A[2] = new Fish();
for (int i = 0; i < A.length; i++)
A[i].move();

Front 98

When mixing objects of difference classes, some access rules are important to know: what are they?

Back 98

Superclass references can always be used to access subclass objects, but NOT vice versa.
Given a reference R of class C, only methods and instance variables that are defined (initially) in class C or ABOVE in the class hierarchy can be accessed through R
They still exist if defined in a subclass, but they are not accessible through R

Front 99

(T/F) Superclass references can always be used to access subclass objects, and vice versa

Back 99

FALSE!

Superclass references can always be used to access subclass objects, but NOT vice versa!

Front 100

Animal A = new Bird();
Bird B = new Animal();

which is ok

Back 100

Animal A = new Bird(); // this is ok
Bird B = new Animal(); // this is an ERROR

Front 101

Suppose class Fish contains a new instance variable waterType and a new method getWaterType()
Fish F = new Fish();
Animal A = new Fish();
System.out.println(F.getWaterType()); ok?
System.out.println(A.getWaterType()); ok?

Back 101

System.out.println(F.getWaterType()); // ok
System.out.println(A.getWaterType()); // NO!

The reason is that the method is not visible from the reference’s point of view (A is an Animal reference so it can only “see” the data and methods defined in class Animal)
System.out.println(((Fish) A).getWaterType());
^ ok, sinc we have now cast the ref to the Fish type, wich CAN acc methd

Front 102

If unsure, test using__________before casting.

Back 102

If unsure, test using instanceof operator before casting

Front 103

Object, Method and Instance Variable Access

Back 103

Superclass references CAN BE used to ref subclass objects
Subclass references CANNOT BE used to ref superclass objects
The type of the ref deter what data and methods are ACCESSIBLE
The type of the object determines what data and methods EXIST
Methods and data initially defined within a subclass CANNOT BE accessed via a superclass reference
The type of the object also determines which VERSION of an overridden method is called

Front 104

Superclass references (CAN BE / CANT BE) used to ref subclass objects

Back 104

Superclass references CAN BE used to ref subclass objects

Front 105

Subclass references (CAN / CANNOT)used to ref superclass objects

Back 105

Subclass references CANNOT BE used to ref superclass objects

Front 106

The _____ determines what data and methods are ______.

Back 106

The type of the reference determines what data and methods are ACCESSIBLE

Front 107

The __________ determines what data and methods _______.

Back 107

The type of the object determines what data and methods EXIST

Front 108

Methods and data initially defined within a subclass (CAN/ CANNOT BE) accessed via a superclass reference

Back 108

Methods and data initially defined within a subclass CANNOT BE accessed via a superclass reference

Front 109

The type of the object also determines which __________of an overridden method is called

Back 109

The type of the object also determines which VERSION of an overridden method is called

Front 110

Sometimes in a class hierarchy, a class may be defined simply to give cohesion to its subclasses
No objects of that class will ever be defined
But instance data and methods will still be inherited by all subclasses, this is called...

Back 110

Abstract classes

Front 111

(T/F) Abstract classes objects may be instantiated

Back 111

FALSE

No objects may be instantiated

Front 112

Java allows only_______ inheritance

Back 112

Java allows only single inheritance

Front 113

We may want to identify an object in multiple ways:
One based on its inherent nature (i.e. its inheritance chain). Make an example

Back 113

Ex: A Person
Others based on what it is capable of doing
Ex: An athlete
Ex: a pilot

Front 114

(T/F) An interface variable can be used to reference any object that implements that interface

Back 114

True However, only the interface methods are accessible through the interface reference

Front 115

An occurrence of an erroneous, unusual or unexpected event in a program execution

Back 115

Exception:

Front 116

Exceptions are objects that are ...

Back 116

Exceptions are objects that are thrown …
and catched

Front 117

Java exception handling.

Exceptions are handled using

Back 117

Exceptions are handled using try-catch blocks

Front 118

If all goes well (no exceptions occur) what block of code is executed?

Back 118

Code in try block is executed, followed by code in (optional) finally block.

If an exception occurs anywhere in the try block
Execution immediately jumps out of the try block.

Front 119

If the exception is not handled in a catch block, the (optional) finally block is executed and then the exception is...

Back 119

propagated

Front 120

Is The Finally block is optional?

Back 120

YES

Front 121

If an exception is handled
Execution resumes immediately AFTER

Back 121

try/catch block in which it was handled, and does NOT return to throw point

Front 122

termination model of exception handling

Back 122

As opposed to a resumption model, where execution resumes from where the exception occurred

Front 123

If an exception is propagated
A handler is searched for by... AKA...

Back 123

backing up through the call chain on the run-time stack. dynamic exception propagation

Front 124

If no exception handler is ever found

Console applications...

GUI applications...

Back 124

Console applications crash and report exception
GUI applications will continue to execute, but may be in an inconsistent state – more soon

Front 125

Checked exceptions

Back 125

If a method does NOT handle these, the method MUST state that it throws them
Done in a throws clause in the method header

These include IOException, and InterruptedException (and their subclasses)
That is why various handouts throughout the term have had some exception handling – it was required

Front 126

Unchecked exceptions

Back 126

Method not required to explicitly "throw" these
These include RunTimeException and Error

Front 127

a method should be able to call itself – we call this a...

Back 127

RECURSIVE CALL