Final Gaddis Chap 3

Question 1

package

Answer 1

a group of related classes

Question 2

the classes in the Java API are organized into

Answer 2

packages

Question 3

the Scanner class is in…

Answer 3

the java.util package

Question 4

Before they can be used, many API classes must be

Answer 4

imported

Question 5

import the Scanner class

Answer 5

import java.util.Scanner;

Question 6

explicit import statements

Answer 6

specify a single class
ex: 
import java.util.Scanner;

Question 7

wildcard import statements

Answer 7

imports all of the classes in a package
ex:
import java.util.*;

Question 8

the java.lang package

Answer 8

• automatically imported into every Java program
• contains general classes such as String and System
• does not need an import statement (automatically imported)

Question 9

Write a call to get an integer from the keyboard and store it in an integer variable num

Answer 9

Scanner scan=new Scanner (System.in);

num=scan.nextint();

Question 10

finding the classes

Answer 10

1) get written description of the problem domain
2) identify all nouns, each is a potential class
3) redefine list to include only classes relevant to the problem

Question 11

identify the responsibilities

Answer 11

1) things a class is responsible for knowing
2) things a class is responsible for doing
3) refine list to include only classes relevant to the problem

Question 12

encapsulation

Answer 12

enclosing the proper attributes and methods inside a single class. All that is necessary for the class to operate

Question 13

encapsulation ensures that

Answer 13

the class is self-contained

Question 14

data hiding

Answer 14

an aspect of encapsulation that uses the private access modifier on fields to hide them from other classes with the idea that classes should not only be self-contained but also self-governing. Methods are needed to allow access and modification of the class’ data

Question 15

Decisions that must be made when designing a class: (5)

Answer 15

1) what data must be accounted for
2) what actions need to be performed
3) what data can be modified
4) what data needs to be accessible
5) any rules as to how data should be modified

Question 16

Class design is typically done with the aid of

Answer 16

a Unified Modeling Language (UML) diagram

Question 17

UML class diagram

Answer 17

a graphical tool that can aid in the design of a class

Question 18

3 main sections for UML diagrams

Answer 18

class name, attributes, methods

Question 19

the data elements of a class

Answer 19

define the object to be instantiated from the class

Question 20

Attributes must be

Answer 20

specific to the class and define it completely
ex:
a rectangle is defined by: length and width

Question 21

Attributes are then

Answer 21

accessed by methods in the class

Question 22

instance

Answer 22

kind of like each use. For example, each instance of the Rectangle class shares the same design, but each instance contains different data.

Question 23

Each instance has

Answer 23

all of the attributes and methods that were defined in the class

Question 24

Classes are defined to represent

Answer 24

a single concept or service

Question 25

A class can be thought of as

Answer 25

a blueprint that objects are created from

Question 26

Constructors

Answer 26

special methods that are used to perform operations at the time an object is created. Constructors typically initialize instance fields and perform other object initialization tasks.

Question 27

If a constructor is not defined

Answer 27

Java provides a default constructor with no parameters

Question 28

Java’s default constructor

Answer 28

sets all the class’ numeric fields to 0, boolean fields to false, reference variables to null

Question 29

default constructors are used to

Answer 29

initialize an object in a default configuration

Question 30

Objects and classes

Answer 30

many objects can be created from a class. Each object is independent of the others
ex:
Rectangle r1=new Rectangle();
Rectangle yellowRectangle=new Rectangle();
Rectangle hersheyBar=new Rectangle();

Question 31

each object is

Answer 31

an address

Question 32

The class’ methods define

Answer 32

the actions that an instance of the class can perform

Question 33

The attributes of a class might need to be

Answer 33

changed, accessed, and calculated

Question 34

the methods that change and access attributes are called

Answer 34

accessors and mutators

Question 35

Because of the concept of data hiding,

Answer 35

fields in a class are private

Question 36

accessors

Answer 36

the methods that retrieve the data of fields

Question 37

mutators

Answer 37

the methods that modify the data of fields

Question 38

An accessor is needed when

Answer 38

the programmer wishes for a field to be viewed by other classes

Question 39

A mutator is needed when

Answer 39

the programmer wishes for a field to be modified

Question 40

accessors and mutators are also called

Answer 40

getters and setters

Question 41

an example of getters and setters

Answer 41

public void setLength (double len)

puble double getLength ()

Question 42

access modifier

Answer 42

a java key word that indicates how a field or method can be accessed

Question 43

3 Java access modifiers

Answer 43

public, private, protected

Question 44

public

Answer 44

states that any other class can access the resource

Question 45

private

Answer 45

indicates that only data within this class can access the resource

Question 46

protected

Answer 46

indicates that only classes in the current package or a class lower in the class hierarchy can access this resource

Question 47

classes that need to be used by other classes are typically made

Answer 47

public

Question 48

if there is more than one class in a file,

Answer 48

only one can be public and it must match the file name

Question 49

typically, the layout of a source code file is

Answer 49

1) attributes
2) methods
- the main method is sometimes 1st, sometimes last
- accessors and mutators are typically grouped

Question 50

exmple of layout

Answer 50

public class Rectangle
{
// instance variables
	//constructor(s) – optional**
 // getters & setters
 // toString – optional**

//** but HIGHLY suggested
}

Question 51

method header format:

Answer 51

accessModifier ReturnType MethodName (Parameters)

Question 52

methods that need to be used by other classes should be made

Answer 52

public

Question 53

example

Answer 53

public class Rectangle
{
private double width;
private double length;

public void setWidth (double w)
{    width = w;
}
public void setLength (double len)
{    length = len;
}
public double getWidth ()
{    return width;
}
public double getLength ()
{    return length;
}

}

Question 54

application

Answer 54

a collection of classes that interact

Question 55

the class that starts the application must have

Answer 55

a main method

Question 56

The class that starts the application can be used as

Answer 56

a driver to test the capabilities of other classes

Question 57

So, you only need a main method when

Answer 57

a program has multiple classes (is an application)

Question 58

Demos

Answer 58

classes that use other classes

Question 59

stale data

Answer 59

data that is the result of calculation of various factors. If you change one of the factors, the overall calculation does not change, making the number stale.
ex: length * width=area
If length changes, area doesn’t. So it is inaccurate and stale

Question 60

to avoid stale data

Answer 60

calculate the value of that data within a method rather than storing it in a variable

Question 61

Application: how to avoid stale data:

Answer 61

public double getArea()
{
return length*width;
}

This dynamically calculates the value of the rectangle’s area when the method is called, so any change to the length or width variables will not leave the area of the rectangle stale

Question 62

Write a program that sets width and length and returns width length and area

Answer 62

public class Rectangle
{
	private double width;
	private double length;

	public void setWidth(double w)
	{	width = w;
	}
	public void setLength(double len)
	{	length = len;
	}
	public double getWidth()
	{	return width;
	}
	public double getLength()
	{	return length;
	}
public double getArea()
	{	return length * width;
	}

}