Chapter 4 - Grouping objects

Question 1

2 points on its usage are:
* you may not remove or add elements while this is iterating a collection. however, we may change the state of an object
* the proper use of this is always with definite iteration. in general we should not be breaking out of this early

Answer 1

give to points to keep in mind when using a for-each loop

Question 2

this is used to add elements to the ArrayList

Answer 2

describe the ArrayList method
.add(object)

Question 3

these include:
1. hasNext()
2. next()
3. remove()

Answer 3

name 3 methods that an iterator will hold

Question 4

this is an object that stores a grouping of object references

Answer 4

what is a
collection

Question 5

this exception may be seen when we try and modify a collection while it is being iterated. such as when using a for-each loop

Answer 5

when might we see the fllowing exception
ConcurrentModificationException

Question 6

when might we see the exception
NullPointerException

Answer 6

this exception might be seen if we tried to call a method on a variable that has not been initialised with an object

Question 7

when this is not initialised the default value it will be given is null

Answer 7

if we declare an object field but do not initialise it within the constructor what value will it be given by default

Question 8

1. this is a reserved java keyword
2. it essentially means: no object or empty

Answer 8

describe the keyword
null

Question 9

describe the string method
concat()

Answer 9

this method appends (concatenate) a string to the end of another string.

Question 10

how can we start using an
**iterator object **
in our program

Answer 10

to begin using this we must import the iterator class that is part of the java standard library using:

Import java.util.Iterator;

Question 11

declaration
Iterator<ElementTypeInCollection> it;

initialisation
it = collection.iterator();

equivalent
Iterator<ElementTypeInCollection> it = collection.iterator();

Answer 11

give psuedocode that
declares and initialise an iterator object

Question 12

glossary quiz

Answer 12

ignore

Question 13

what is a
collection

Answer 13

this is an object that stores a grouping of object references

Question 14

if we declare an object field but do not initialise it within the constructor what value will it be given by default

Answer 14

when this is not initialised the default value it will be given is null

Question 15

what will the
iterator() methodof collections return

Answer 15

this will retuen an iterator object for that collection

Question 16

this is the combination of a generic type and a generic type parameter to create a new type

Answer 16

what is a
specific type

Question 17

how is the
diamond notation
used

Answer 17

this will either:
* hold a generic type parameter
* or be left empty if we have already declared the type parameter

Question 18

what is a
generic class also referred to as

Answer 18

this is also referred to as a
parameterized type
because it receives a type as a parameter when it is declared.

Question 19

the syntax for this is:

do {  
    // code block to be executed}
while (condition);

Answer 19

what is the syntax for the
do-while loop

Question 20

what are
generic type parameters

Answer 20

Atypegiven betweenangle bracketsto make ageneric typespecific.

Question 21

how does the
for-each loop get its name

Answer 21

this gets its name from the way it is read:
~~~
For each element in collection do{
loop body
}
~~~

Question 22

what code can be used as validation which
ensures we do not recieve an IndexOutOfBoundsException

Answer 22

what does the following validation code ensure:

If(index >=0 && index < collection.size())
{
    We have a valid index
}

Question 23

1. this involves an indefinite number of iterations
2. this implies that a while loop would be better suited than a for-each loop

Answer 23

give two properties of searching a collection

Question 24

when using an iterator do we require our own index value

Answer 24

when iterating a collection using this it will itself keep track of where it is and so using our own index is unnecessary

Question 25

what are the two outcomes of searching a collection and how might we express this in code

Answer 25

the two outcomes of this are:
* The search succeeds after an indefinte number of iterations
* The search fails after the collection has been exhausted

both must be taken into account during the search and so the code may look as follows

Int index = 0
Boolean searching = True;
While(searching && index < file.size())

Question 26

the syntax for this is
string.concat(string2)

@param string2 the string to append to the first string

Answer 26

what is the syntax for the string method
concat()

Question 27

this will remove the element it last passed

Answer 27

describe the iterator method
remove()

Question 28

what two things must be specified when declaring a collection

Answer 28

when declaring this we must specify:
1.The type of the collection (I.e ArrayList)
2.The type of the elements that will be stored in the collection (generic type parameter)

Question 29

this is an object that allows us to iterate over different types of collections

Answer 29

what is an
iterator

Question 30

describe
definite iteration

Answer 30

this is when we know beforehand how many iterations will occur.

for-each loops are a perfect application for this type of iteration as we know it will iterate as many times as the size of a collection

Question 31

when iterating a collection using this it will itself keep track of where it is and so using our own index is unnecessary

Answer 31

when using an iterator do we require our own index value

Question 32

this can be a more concise way to write code. and invloves a method returning an anonymous object that can be used by the next method call

example:
String A = Method1()
String B = A.Method2()
String C = B.Method3()

String c = method1().method2().method3()

Here each method returns an anonymous object instead of the first method where we used a reference for each returned object

Answer 32

describe
chaining methods

Question 33

write a method that returns the parameterized type ArrayList<String>
which will hold the first two objects from the collection named library

Answer 33

the code to achieve this is:

public ArrayList<String> firstTwo(){
    ArrayList<String> temp = new ArrayList<>();
    temp.add(library.get(0));
    temp.add(library.get(1));

    return temp;
}

Question 34

this gets its name from the way it is read:
~~~
For each element in collection do{
loop body
}
~~~

Answer 34

how does the
for-each loop get its name

Question 35

when might we see the fllowing exception
ConcurrentModificationException

Answer 35

this exception may be seen when we try and modify a collection while it is being iterated. such as when using a for-each loop

Question 36

what is the wording if we have the following
1.Collection = ArrayList
2.Objects / Elements it will hold = String
~~~
ArrayList<String>;
~~~</String>

Answer 36

this can be read as
an “ArrayList of String”

Question 37

this will return the next element of the collection and then move past it

Answer 37

describe the iterator method
next()

Question 38

what does the following validation code ensure:

If(index >=0 && index < collection.size())
{
    We have a valid index
}

Answer 38

what code can be used as validation which
ensures we do not recieve an IndexOutOfBoundsException

Question 39

this can be achieved using:
declaration
ArrayList<String> someString;
initialisation
someString = new ArrayList<>();

Answer 39

(la) 1. declare anArrayListof some type of element
2. then initialise anArrayListusing the diamond notation

Question 40

what check can be made to avoid
null errors

Answer 40

to avoid these use a check such as:
If (var == null)

Question 41

(la) 1. declare anArrayListof some type of element
2. then initialise anArrayListusing the diamond notation

Answer 41

this can be achieved using:
declaration
ArrayList<String> someString;
initialisation
someString = new ArrayList<>();

Question 42

why do we not require our own index when using an iterator

Answer 42

this is not required because the iterator is itself aware and keeping track of its position within a collection

Question 43

describe the
do-while loop
and how it operates

Answer 43

this is a variant of the while loop and operates as follows:
1. It will first execute a block of code (do)
2. Then it will check if a condition is true (while)
3. If the condition is true it will again execute the do block of code
4. This continues until the condition is false

Question 44

these include:
* .add(object)
* .get(index)
* .remove(index)
* .size()

Answer 44

name 4 methods of the ArrayList

Question 45

positive

Boolean searching = True;
While(searching)

negative

Boolean found = False;
While(!found)

both are equivalent but they are expressed differently and is something that must be kept in mind for readability of the problem

Answer 45

give examples of positive and negative boolean expressions

Question 46

this is considered incomplete because for it to function it must be passed a second type as a parameter
providing a second type will complete this

Answer 46

why is a generic type class considered incomplete and how would we complete it

Question 47

describe the ArrayList method
.get(index)

Answer 47

this is used to access an element in the ArrayList

Question 48

what is an important note concerning iterating a collection using an iterator

Answer 48

an important note when performing this is:

that all interaction with the collection is done using the iterator we never directly access the collection

Question 49

what exception will be shown if we try and

access an index of a collection that is equal to or greater than its size

Answer 49

in this case we will see the exception:
IndexOutOfBoundsException

Question 50

to avoid these use a check such as:
If (var == null)

Answer 50

what check can be made to avoid
null errors

Question 51

what is
garbage collection

Answer 51

this is a runtime system that reclaims memory from objects that have no references to them (anonymous objects)

Question 52

describe the keyword
null

Answer 52

1. this is a reserved java keyword
2. it essentially means: no object or empty

Question 53

this is not required because the iterator is itself aware and keeping track of its position within a collection

Answer 53

why do we not require our own index when using an iterator

Question 54

give examples of positive and negative boolean expressions

Answer 54

positive

Boolean searching = True;
While(searching)

negative

Boolean found = False;
While(!found)

both are equivalent but they are expressed differently and is something that must be kept in mind for readability of the problem

Question 55

ignore

Answer 55

glossary quiz

Question 56

this is a class that does not define a single type but can be many types.

this is because it is actually composed of two types being:
1. itself
2. and a second type we provide it

when a generic type is declared and given a second type, the combination makes a new type

we then refer to this as a specific type

Answer 56

what is a generic class

Question 57

this is used to removes an element from the given index

Answer 57

describe the ArrayList method
.remove(index)

Question 58

what is the
syntax of the for-each loop

Answer 58

syntax is:
~~~
For (ElementType element : collection) {
Loop body
}
~~~

example is:
~~~
For (String fileName : files) {
System.out.println(fileName);
}
~~~

Question 59

this is a variant of the while loop and operates as follows:
1. It will first execute a block of code (do)
2. Then it will check if a condition is true (while)
3. If the condition is true it will again execute the do block of code
4. This continues until the condition is false

Answer 59

describe the
do-while loop
and how it operates

Question 60

this will return the number of elements in the ArrayList

Answer 60

describe the ArrayList method
.size()

Question 61

describe how an iterator positions itself within a collection and give three points concerning
1. where it starts
2. how it moves to the next element
3. what happens when we ask the iterator to remove an element from the collection

Answer 61

1.It sets itself before the first element
2.When next() is called it returns the element in front of it then moves past it but stays before the second element
3.If we told this to remove an item it would remove the item it last passed

Question 62

how can we use an ArrayList

Answer 62

this is not strictly part of java but is included in the java standard library so to use it we must import it using:
import java.util.ArrayList;

Question 63

in this case we will see the exception:
IndexOutOfBoundsException

Answer 63

what exception will be shown if we try and

access an index of a collection that is equal to or greater than its size

Question 64

this is a runtime system that reclaims memory from objects that have no references to them (anonymous objects)

Answer 64

what is
garbage collection

Question 65

1.It sets itself before the first element
2.When next() is called it returns the element in front of it then moves past it but stays before the second element
3.If we told this to remove an item it would remove the item it last passed

Answer 65

describe how an iterator positions itself within a collection and give three points concerning
1. where it starts
2. how it moves to the next element
3. what happens when we ask the iterator to remove an element from the collection

Question 66

describe the ArrayList method
.add(object)

Answer 66

this is used to add elements to the ArrayList

Question 67

to begin using this we must import the iterator class that is part of the java standard library using:

Import java.util.Iterator;

Answer 67

how can we start using an
**iterator object **
in our program

Question 68

describe the iterator method
next()

Answer 68

this will return the next element of the collection and then move past it

Question 69

are the following two fields the same type, explain the answer

Private ArrayList<Person> members;
Private ArrayList<TicketMachine> machines;

Answer 69

these are not the same type:
1. they are composed of the same generic type (ArrayList)
2. but the generic type paramaters are differrent and so we have created two different specific types

Question 70

this is when we are uncertain about how many iterations will happen. while loops are suited to this type of iteration as we can base the iteration on a condition

Answer 70

describe
indefinite iteration

Question 71

describe the ArrayList method
.remove(index)

Answer 71

this is used to removes an element from the given index

Question 72

ArrayList includes this because it is a general purpose class or “generic type” this means it is not restricted in what types it can store but we must include the type via this

Answer 72

why does
ArrayList include a generic type parameter

Question 73

(la) use animportstatement to gain access to a library class

Answer 73

This can be achieved using the keyword “import” followed by the qualified name of the package

Question 74

This can be achieved using the keyword “import” followed by the qualified name of the package

Answer 74

(la) use animportstatement to gain access to a library class

Question 75

the syntax for this is:

while(booleanCondition) {
    Loop body
}

Answer 75

what is the
syntax of a while loop

Question 76

the purpose of this is so that we can iterate over a collection and perform actions on every element inside the collection

Answer 76

describe the purpose of the
for-each loop

Question 77

describe
chaining methods

Answer 77

this can be a more concise way to write code. and invloves a method returning an anonymous object that can be used by the next method call

example:
String A = Method1()
String B = A.Method2()
String C = B.Method3()

String c = method1().method2().method3()

Here each method returns an anonymous object instead of the first method where we used a reference for each returned object

Question 78

what is the naming convention when using a getter method to get a boolean value

Answer 78

the convention for this is to prepend the word “is” to the methods name

Question 79

Atypegiven betweenangle bracketsto make ageneric typespecific.

Answer 79

what are
generic type parameters

Question 80

an important note when performing this is:

that all interaction with the collection is done using the iterator we never directly access the collection

Answer 80

what is an important note concerning iterating a collection using an iterator

Question 81

give psuedocode that
declares and initialise an iterator object

Answer 81

declaration
Iterator<ElementTypeInCollection> it;

initialisation
it = collection.iterator();

equivalent
Iterator<ElementTypeInCollection> it = collection.iterator();

Question 82

this is when we know beforehand how many iterations will occur.

for-each loops are a perfect application for this type of iteration as we know it will iterate as many times as the size of a collection

Answer 82

describe
definite iteration

Question 83

this is also referred to as a
parameterized type
because it receives a type as a parameter when it is declared.

Answer 83

what is a
generic class also referred to as

Question 84

why is a generic type class considered incomplete and how would we complete it

Answer 84

this is considered incomplete because for it to function it must be passed a second type as a parameter
providing a second type will complete this

Question 85

this can be read as
an “ArrayList of String”

Answer 85

what is the wording if we have the following
1.Collection = ArrayList
2.Objects / Elements it will hold = String
~~~
ArrayList<String>;
~~~</String>

Question 86

give two properties of searching a collection

Answer 86

1. this involves an indefinite number of iterations
2. this implies that a while loop would be better suited than a for-each loop

Question 87

describe the iterator method
hasNext()

Answer 87

this will check whether the collection has a next element

note: important to use this before moving to the next element

Question 88

(la) explain the purpose of a collection

Answer 88

the purpose of this is to hold many references to objects

Question 89

an iterator has been initialised with the identifier “it”
use it to iterate the collection it is from using a while loop
note: in pseudocode

Answer 89

this can be achieved using:

While (it.hasNext()) {
    Call it.next() to get the next element and hold it in variable
    Do something to that element
}

Question 90

describe
indefinite iteration

Answer 90

this is when we are uncertain about how many iterations will happen. while loops are suited to this type of iteration as we can base the iteration on a condition

Question 91

describe the iterator method
remove()

Answer 91

this will remove the element it last passed

Question 92

the code to achieve this is:

public ArrayList<String> firstTwo(){
    ArrayList<String> temp = new ArrayList<>();
    temp.add(library.get(0));
    temp.add(library.get(1));

    return temp;
}

Answer 92

write a method that returns the parameterized type ArrayList<String>
which will hold the first two objects from the collection named library

Question 93

what is a
specific type

Answer 93

this is the combination of a generic type and a generic type parameter to create a new type

Question 94

when declaring this we must specify:
1.The type of the collection (I.e ArrayList)
2.The type of the elements that will be stored in the collection (generic type parameter)

Answer 94

what two things must be specified when declaring a collection

Question 95

what is the syntax for the string method
concat()

Answer 95

the syntax for this is
string.concat(string2)

@param string2 the string to append to the first string

Question 96

these include:
* A while loop does not have to be tied to a collection (we can loop on any condition as long as we can create a boolean expression)
* If we are using a while loop to iterate a collection we can abort early in an elegant way

Answer 96

name 2
benefits the while loop has over the for-each loop

Question 97

syntax is:
~~~
For (ElementType element : collection) {
Loop body
}
~~~

example is:
~~~
For (String fileName : files) {
System.out.println(fileName);
}
~~~

Answer 97

what is the
syntax of the for-each loop

Question 98

these are not the same type:
1. they are composed of the same generic type (ArrayList)
2. but the generic type paramaters are differrent and so we have created two different specific types

Answer 98

are the following two fields the same type, explain the answer

Private ArrayList<Person> members;
Private ArrayList<TicketMachine> machines;

Question 99

describe the purpose of the
for-each loop

Answer 99

the purpose of this is so that we can iterate over a collection and perform actions on every element inside the collection

Question 100

these include:
1.Ordered - meaning the objects can be accessed by using the position they are placed in
2.all elements are of same type - all items (elements) stored in this collection object will be of the same type
3.Infinite capacity - many elements can be added without a limit (except the hardware itself)

Answer 100

give three
properties of ArrayList

Question 101

give three
properties of ArrayList

Answer 101

these include:
1.Ordered - meaning the objects can be accessed by using the position they are placed in
2.all elements are of same type - all items (elements) stored in this collection object will be of the same type
3.Infinite capacity - many elements can be added without a limit (except the hardware itself)

Question 102

why does
ArrayList include a generic type parameter

Answer 102

ArrayList includes this because it is a general purpose class or “generic type” this means it is not restricted in what types it can store but we must include the type via this

Question 103

the convention for this is to prepend the word “is” to the methods name

Answer 103

what is the naming convention when using a getter method to get a boolean value

Question 104

(la) understand how a generic type relates to a specific type and a generic type parameter

Answer 104

1. A generic type is a class that requires a type as a parameter.
2. When the type is passed to it it becomes a specific type.
3. We pass the type to the generic type within angle brackets known as diamond notation.
4. What is passed inside the angle brackets is known as the generic type parameter

Question 105

this will retuen an iterator object for that collection

Answer 105

what will the
iterator() methodof collections return

Question 106

this is used to access an element in the ArrayList

Answer 106

describe the ArrayList method
.get(index)

Question 107

this method appends (concatenate) a string to the end of another string.

Answer 107

describe the string method
concat()

Question 108

give two benefits that give an iterator its power and usefullness

Answer 108

these include:
1. While we can iterate an array list using our own index there are other collections where providing our own index is either impossible or inefficient this is where the power of the iterator comes into play
2.Using an iterator allows us to safely remove elements from a collection while we iterate it. A for-each loop would throw an error if we used a collections remove method this is not the case when we use an iterator to do the removal for us

Question 109

this is not strictly part of java but is included in the java standard library so to use it we must import it using:
import java.util.ArrayList;

Answer 109

how can we use an ArrayList

Question 110

1. A generic type is a class that requires a type as a parameter.
2. When the type is passed to it it becomes a specific type.
3. We pass the type to the generic type within angle brackets known as diamond notation.
4. What is passed inside the angle brackets is known as the generic type parameter

Answer 110

(la) understand how a generic type relates to a specific type and a generic type parameter

Question 111

this can be achieved using:

While (it.hasNext()) {
    Call it.next() to get the next element and hold it in variable
    Do something to that element
}

Answer 111

an iterator has been initialised with the identifier “it”
use it to iterate the collection it is from using a while loop
note: in pseudocode

Question 112

what is the syntax for the
do-while loop

Answer 112

the syntax for this is:

do {  
    // code block to be executed}
while (condition);

Question 113

this will either:
* hold a generic type parameter
* or be left empty if we have already declared the type parameter

Answer 113

how is the
diamond notation
used

Question 114

what is an
iterator

Answer 114

this is an object that allows us to iterate over different types of collections

Question 115

these are libraries that come with a programming language and contain hundreds or thousands of classes that have become useful to the language. In Java these classes are contained in what are called packages and are used in the same way we would use our own classes

Answer 115

what are
class libraries

Question 116

name 2
benefits the while loop has over the for-each loop

Answer 116

these include:
* A while loop does not have to be tied to a collection (we can loop on any condition as long as we can create a boolean expression)
* If we are using a while loop to iterate a collection we can abort early in an elegant way

Question 117

the purpose of this is to hold many references to objects

Answer 117

(la) explain the purpose of a collection

Question 118

give to points to keep in mind when using a for-each loop

Answer 118

2 points on its usage are:
* you may not remove or add elements while this is iterating a collection. however, we may change the state of an object
* the proper use of this is always with definite iteration. in general we should not be breaking out of this early

Question 119

what is the
syntax of a while loop

Answer 119

the syntax for this is:

while(booleanCondition) {
    Loop body
}

Question 120

what is a generic class

Answer 120

this is a class that does not define a single type but can be many types.

this is because it is actually composed of two types being:
1. itself
2. and a second type we provide it

when a generic type is declared and given a second type, the combination makes a new type

we then refer to this as a specific type

Question 121

describe the ArrayList method
.size()

Answer 121

this will return the number of elements in the ArrayList

Question 122

this will return the character at the specified index of the string

Answer 122

describe the
String.charAt(index)
method

Question 123

this exception might be seen if we tried to call a method on a variable that has not been initialised with an object

Answer 123

when might we see the exception
NullPointerException

Question 124

these include:
1. While we can iterate an array list using our own index there are other collections where providing our own index is either impossible or inefficient this is where the power of the iterator comes into play
2.Using an iterator allows us to safely remove elements from a collection while we iterate it. A for-each loop would throw an error if we used a collections remove method this is not the case when we use an iterator to do the removal for us

Answer 124

give two benefits that give an iterator its power and usefullness

Question 125

describe the
String.charAt(index)
method

Answer 125

this will return the character at the specified index of the string

Question 126

the two outcomes of this are:
* The search succeeds after an indefinte number of iterations
* The search fails after the collection has been exhausted

both must be taken into account during the search and so the code may look as follows

Int index = 0
Boolean searching = True;
While(searching && index < file.size())

Answer 126

what are the two outcomes of searching a collection and how might we express this in code

Question 127

name 3 methods that an iterator will hold

Answer 127

these include:
1. hasNext()
2. next()
3. remove()

Question 128

what are
class libraries

Answer 128

these are libraries that come with a programming language and contain hundreds or thousands of classes that have become useful to the language. In Java these classes are contained in what are called packages and are used in the same way we would use our own classes

Question 129

name 4 methods of the ArrayList

Answer 129

these include:
* .add(object)
* .get(index)
* .remove(index)
* .size()

Question 130

this will check whether the collection has a next element

note: important to use this before moving to the next element

Answer 130

describe the iterator method
hasNext()