Java 2 Declarations And Access Control

Front 1

How many public classes can you have per source code file?

Back 1

one

Front 2

What must the name of the source code file be that contains a public class?

Back 2

It must match the name of the public class.

Front 3

How do you make a class a part of a package?

Back 3

You must have the package statement as the first line in the source code file.

Front 4

Where do "import" statements go in a source code file?

Back 4

Between the package statement and the class declaration. If there isn't a package statement, then the import statement(s) must be the first line(s) in the source code file.

Front 5

If there are no package or import statements, what must be the first line in the source code file?

Back 5

the class declaration

Front 6

Give the 3 access modifiers.

Back 6

public, protected, private

Front 7

Give 3 nonaccess modifiers.

Back 7

strictfp, final, abstract

Front 8

There are ____ access controls but only ____ access modifiers.

Back 8

four
three

Front 9

What is the "default" or "package access"?

Back 9

What you get when you don't use any of the three access modifiers.

Front 10

What kind of access can a class have?

Back 10

"public" or "default" access

Front 11

How does Sun recommend that you name your packages?

Back 11

Use reverse domain names, appended with division and/or project names.

Front 12

What does it mean for a class to have "default" access?

Back 12

package-level access - a class with default access can be seen only by classes within the same package

Front 13

What happens when a class in package A tries to access a default class in package B.

Back 13

You get a compilation error.

Front 14

What does a class declaration with the "public" keyword do?

Back 14

Gives all classes from all packages access to the public class.

Front 15

What do you need to do to access a public class in another package?

Back 15

You need to import the public class.

Front 16

Can you use "strictfp" in combination with "abstract" or "final" as class modifiers?

Back 16

Yes

Front 17

Can you use both "final" and "abstract" together as class modifiers?

Back 17

No

Front 18

What does it mean to mark a class as "strictfp"?

Back 18

It means that any method code in the class will conform to the IEEE754 standard rules for floating point. Without it, floating points used in the methods might behave in a platform-dependent way.

Front 19

What does it mean to use the "final" keyword in a class declaration?

Back 19

It means the class can't be subclassed, i.e. no other class can ever "extend" a "final" class and any attempts to do so will give you a compiler error.

Front 20

Why would you mark a class as "final"?

Back 20

You need an absolute guarantee that "none" of the methods in that class will ever be overridden.

Front 21

Name a class in the Java core libraries that is "final".

Back 21

the java.lang.String class

Front 22

A "final" class obliterates a key benefit of OO - _________.

Back 22

extensibility

Front 23

Can an "abstract" class be instantiated?

Back 23

No, you'll get a compiler error

Front 24

What is an "abstract" class' sole mission in life?

Back 24

to be extended (subclassed)

Front 25

How do methods that are marked "abstract" end?

Back 25

they end in a semicolon rather than curly braces

Front 26

If a method declaration ends with a semicolon rather than curly braces and it is in a class (as opposed to an interface), how must the method and class be marked?

Back 26

they must both be marked as "abstract"

Front 27

If even a single method is "abstract", the whole class must be declared ______.

Back 27

"abstract"

Front 28

Can you put nonabstract methods in an abstract class?

Back 28

Yes

Front 29

Why can't you mark a class as both "abstact" and "final"?
What happens if you do this?

Back 29

They have nearly opposite meanings. An abstract class must be subclassed, whereas a final class must not be subclassed.
The code will not compile.

Front 30

What are the members of a class?

Back 30

its methods and instance (nonlocal) variables

Front 31

How many access control levels can the members of a class use?

Back 31

all four: public, protected, default, and private

Front 32

If class A itself can't be accessed by class B, can any members of class A be accessed by class B?

Back 32

no, not even if the member is declared "public".

Front 33

What does it mean to declare a member of a class "public"?

Back 33

It means all other classes, regardless of the package they belong to can access the member (assuming the class itself is visible).

Front 34

If a member of a superclass is declared "public", does a subclass inherit that member?

Back 34

Yes, regardless of whether both classes are in the same package.

Front 35

What does the reference "this" refer to?

Back 35

It always refers to the currently executing object - the object running the code where you see the "this" reference.

Front 36

What does it mean to see a method invoked (or a variable accessed) without the dot operator (.)?

Back 36

It means that the method or variable belongs to the class where you see that code. It also means that the method or variable is implicitly being accessed using the "this" reference.

Front 37

What does it mean for a member of a class to be marked "private"?

Back 37

It means the member can't be accessed by code in any class other than the class in which the private member was declared.

Front 38

Can a subclass inherit a private member?

Back 38

No

Front 39

Is it good practice to mark an instance variable as "public"?

Back 39

No, it's nearly always best to keep all instance variables "private" or "protected".

Front 40

What should a programmer use if an instance variable needs to be changed?

Back 40

Should use public accessor methods, like "get<propertyName>" or "set<propertyName>"

Front 41

Can a "private" method be overridden?

Back 41

No, since a subclass cannot inherit a "private" method.

Front 42

What is the critical difference between "protected" and "default" members?

Back 42

A "default" member may be accessed only if the class accessing the member belongs to the same package whereas a "protected" member can be accessed (through inheritance) by a subclass even if the subclass is in a different package.

Front 43

When you think of "default" access, think ______ restriction. But when you think "protected", think _____ + ____.

Back 43

package
package kids

Front 44

If a subclass-outside-the-package gets a reference to the superclass, can the subclass use the dot operator on the superclass reference to access a protected member of the superclass?

Back 44

No, the subclass can only see a "protected" member through inheritance.

Front 45

Once the subclass-outside-the-package inherits a protected member, that member (as inherited by the subclass) becomes _______ to any code outside the subclass, with the exception of subclasses of the subclass.

Back 45

private

Front 46

"default" members are visible only to the subclasses that are in the same ______ as the superclass.

Back 46

package

Front 47

Can an access modifier be applied to local variables?

Back 47

No, you will get a compiler error.

Front 48

What is the only modifier that can ever be applied to local variables?

Back 48

final

Front 49

What does the "final" keyword do for a method?

Back 49

It prevents a method from being overridden in a subclass, and is often used to enforce the API functionality of a method.

Front 50

What happens when a subclass tries to override a "final" method of its superclass?

Back 50

You get a compiler error

Front 51

Method arguments are essentially the same as _______.

Back 51

local variables

Front 52

What must be true of a final argument to a method?

Back 52

It must keep the same value that the parameter had when it passed into the method.

Front 53

What is an "abstract" method?

Back 53

A method that's been declared (as abstract) but not implemented. It has a semicolon instead of curly braces for where the implementation code goes.

Front 54

What must be true about a class that has an abstract method?

Back 54

It must be declared "abstract" also.

Front 55

Why would you mark a method "abstract"?

Back 55

when you want to force subclasses to provide the implementation

Front 56

Can you hava an "abstract" class with no "abstract" methods?

Back 56

Yes

Front 57

The first concrete subclass of an "abstract" class must do what?

Back 57

It must implement all abstract methods of the superclass. Any class that extends an abstract class must do this unless the subclass is also abstract.

Front 58

A method can never be marked as both "abstract" and _____, or "abstract" and _____.

Back 58

final
private

Front 59

What must be true about a class that has an abstract method?

Back 59

It must be declared "abstract" also.

Front 60

Why would you mark a method "abstract"?

Back 60

when you want to force subclasses to provide the implementation

Front 61

Can you hava an "abstract" class with no "abstract" methods?

Back 61

Yes

Front 62

The first concrete subclass of an "abstract" class must do what?

Back 62

It must implement all abstract methods of the superclass. Any class that extends an abstract class must do this unless the subclass is also abstract.

Front 63

A method can never be marked as both "abstract" and _____, or "abstract" and _____. Why?

Back 63

final
private
"abstract" methods must be implemented(which essentially means overridden by a subclass) whereas "final" and "private" methods cannot ever be overridden

Front 64

"abstract" methods say nothing about the implementation, so they cannot be marked as _____, _____, or ______.

Back 64

synchronized
strictfp
native

Front 65

Can you combine the "abstract" modifier with the "static" modifier?

Back 65

No

Front 66

What does the "synchronized" keyword on a method indicate?

Back 66

It indicates that a method can be assessed by only one thread at a time.

Front 67

Can the "synchronized" modifier be applied to variables or classes?

Back 67

No - only to methods

Front 68

Can you use "synchronized" with "abstract"?

Back 68

No, since sychronization is an implementation issue.

Front 69

Can you combine "synchronized" with "final"?

Back 69

Yes

Front 70

What does the "native" modifier indicate about a method?

Back 70

that a method is implemented in a platform-dependent language, such as C

Front 71

"native" can never be combined with _____, and "native" can only be applied to _____.

Back 71

abstract
methods

Front 72

What is a "native" method's body?

Back 72

must be a ";" (like "abstract" methods), indicating that the implemtation is omitted

Front 73

What can "strictfp" modify?

Back 73

a class or nonabstract methods, a variable can never be declared "strictfp"

Front 74

What does "strictfp" do?

Back 74

It forces floating points (and any floating-point operations) to adhere to the IEEE754 standard.

Front 75

Where are "instance variables" defined and when are they initialized?

Back 75

They are defined inside the class, but outside of any method, and are only initialzed when the class is instantiated. They are the "fields" that belong to each unique object.

Front 76

What 2 non-access modifiers can be used with "instance variables"?

Back 76

"final" and "transient"

Front 77

What 4 non-access modifiers cannot be used with "instance variables"?

Back 77

abstract
synchronized
strictfp
native

Front 78

Where are local variables declared and where do they live?

Back 78

They are declared within a method and they live on the stack.

Front 79

If a local variable is an object reference, where will the object be created?

Back 79

On the heap, there is no such thing as a stack "object", only a stack "variable"

Front 80

local variables can't use most of the modifiers that can be applied to instance variables but they can be marked ____.

Back 80

final

Front 81

What must be done before a local variable can be used?

Back 81

It must be initialized. local variables don't get default values.

Front 82

What is it called when a local variable is declared with the same name as an instance variable?

Back 82

shadowing

Front 83

What does it mean to declare a variable "final"?

Back 83

It makes it impossible to reinitialize that variable once it has been initialized with an explicit value.

Front 84

What does it mean to mark an object reference variable final?

Back 84

It can't ever be reassigned to refer to a different object. However, the data within the object can be modified.

Front 85

What does a reference variable hold?

Back 85

bits that represent, in a platform-dependent format, a way to get to an object

Front 86

What must be done if you declare a "final" instance variable by the time the constructor completes?

Back 86

you're obligated to give it an explicit value.
Note: a final variable isn't given a default value.

Front 87

If you declare an instance variable "final", but don't give it an explicit value at the time you declare it, the variable is considered a _____ final.

Back 87

blank
It can stay blank only until the constructor completes

Front 88

Variables declared in an interface are always implicitly _____.

Back 88

final

Front 89

Interface variables are always implicitly ____ _____ _____.

Back 89

public static final

Front 90

What does it mean to mark an instance variable as "transient"?

Back 90

you're telling the JVM to skip (ignore) this variable when you attempt to serialize the object declaring it

Front 91

The keyword "transient" can only be applied to _______.

Back 91

instance variables

Front 92

What is serialization?

Back 92

It lets you save (sometimes called "flatten") an object by writing its state (in other words its instance variables) to a special type of IO stream.

Front 93

What does the "volatile" modifier do?

Back 93

it tells the JVM that a thread accessing the variable must always reconcile its own private copy of the variable with the master copy in memory. It can only be applied to instance variables

Front 94

What do "static" variables and methods belong to?

Back 94

the class rather than to any particular instance. You can use a static method or variable without having any instances of that class at all.

Front 95

How many copies are there of a "static" variable?

Back 95

one, it will be shared by all instances of the class

Front 96

When is a "static" instance variable set to zero?

Back 96

When the class it is in is first loaded by the JVM before any instances are created.

Front 97

Making the method called by the JVM (main()) a static method means what?

Back 97

the JVM doesn't have to create an instance of your class just to start running code.

Front 98

Can you access an instance variable (non-static) from the static main() method?

Back 98

No, main() doesn't know anything about any instances so it can't access the variables. You will get a compile error.

Front 99

A "static" method of a class can't access a ______ member of
its own class.

Back 99

non-static (instance) - method or variable

Front 100

How do we access a "static" method (or "static" variable)?

Back 100

Use the dot operator on the class name, as opposed to on a reference to an instance.
Note: however, you are allowed to use an object reference variable to access a static member.

Front 101

What are 3 things you can mark as "static"?

Back 101

methods, variables, top-level nested classes

Front 102

What are 6 things you cannot mark as "static"?

Back 102

constructors
classes
interfaces
inner classes
inner class methods and instance variables
local variables

Front 103

How many package statements can there be per source code file?

Back 103

one

Front 104

If there is no "public" class in your source code file, how can you name your file?

Back 104

you can name it whatever you like

Front 105

Does the order of the classes in a source code file matter?

Back 105

No

Front 106

When would you group several classes into a single source code file?

Back 106

when those classes should only be used together as one component

Front 107

Do package and import declarations apply to all classes in a source code file?

Back 107

Yes

Front 108

When you put a class in a package (through the package declaration) you essentially give the class a longer name, which we call the _______________.

Back 108

fully qualified name

Front 109

What are the 2 ways you can eliminate confusion about which class you want in your code?

Back 109

1. Use an "import" statement
2. Use the fully qualified name throughout your code

Front 110

What is the order in which the compiler resolves imports?

Back 110

Explicit imports are resolved first, then the classes from the current package, and last - the implicit imports (wildcard package imports)

Front 111

What do you have to do if you want to use two classes with the same name from two different packages?

Back 111

you have to use the fully qualified names

Front 112

List 5 rules that apply to the "main()" method.

Back 112

1. It must be marked "static"
2. It must have a "void" return type
3. It must have a single String array argument
4. You can name the argument anything you like
5. It should be declared "public" and for the exam, assume it must be "public"

Front 113

If the JVM can't find you "main()" method, what happens?

Back 113

You get a runtime error - the NoSuchMethodError

Front 114

What must the signature of your "main()" method look like if you want the JVM to run your class?

Back 114

public static void main(String[] args) {}
otherwise you get a runtime error
Note: you can write "static public" instead of "public static" and you can give the argument "args" a different name

Front 115

What is the signature of the one and only java.lang.Runnable interface method?

Back 115

public void run(){}

Front 116

When you create an interface, you're defining a ______ for what a class can do.

Back 116

contract

Front 117

Can interfaces be implemented by any class, from any inheritance tree?

Back 117

Yes - this lets you take radically different classes and give them a common characteristic.

Front 118

Can an interface have both abstract and nonabstract methods?

Back 118

No - only abstract methods so they must end with a semicolon rather than curly braces

Front 119

All interface methods are implicitly ______ and ______.

Back 119

public
abstract

Front 120

Can interface methods be static?

Back 120

No

Front 121

Do you need to type the "public" or "abstract" modifiers in the method declarations of interface methods?

Back 121

No

Front 122

All variables defined in an interface must be _____, _____,
and _____.

Back 122

public, static, and final - in other words they must be constants, not instance variables

Front 123

Because interface methods are abstract, they cannot be marked ____, _____, ______, or _____.

Back 123

final, native, strictfp, synchronized

Front 124

Can an interface method extend one or more other interfaces?

Back 124

Yes

Front 125

What is the only thing that an interface can extend?

Back 125

another interface

Front 126

Can an interface implement another interface or class?

Back 126

No

Front 127

What keyword must you use to declare an interface?

Back 127

"interface"

Front 128

Can interface types be used polymorphically?

Back 128

Yes

Front 129

Is the "abstract" modifier required in an interface declaration?

Back 129

No - interfaces are implicitly abstract

Front 130

When is the "public" modifier required on a interface declaration?

Back 130

When you want the interface to have public rather than default access.

Front 131

Do you need to explicitly declare interface constants as "public", "static", and "final"?

Back 131

No

Front 132

Can an interface variable be given a value by the implementing class?

Back 132

No - they are final

Front 133

If you create a class that implements the "Runnable" interface, what must you provide?

Back 133

the "public void run()" method

Front 134

If a class implements an interface, what must it do?

Back 134

It must have an implementation for each method in the interface

Front 135

What 4 things must a nonabstract implementation class do to be a legal implementation class?

Back 135

1. Provide concrete(nonabstract) implementation for all methods from the declared interface
2. Follow all the rules for legal overrides
3. Declare no checked exceptions on implementation methods other than those declared by the interface method, or subclasses of those declared by the interface method.
4. Maintain the signature of the interface method and maintain the same return type (but does not have to declare the exceptions declared in the interface method declaration).

Front 136

Can an implementation class be abstract?

Back 136

Yes - then it doesn't need to provide the implementation methods but can pass the buck to its first concrete class

Front 137

You can extend only one _____ but ______ many interfaces.

Back 137

class
implement

Front 138

Can an interface extend another interface?

Back 138

Yes - the subinterface simply adds more requirements to the contract of the superinterface.

Front 139

Can an interface extend more than one interface?

Back 139

Yes