Scjp 6 (310-065) Chapter 1 Declarations And Access Control

Front 1

What is an identifier?

Back 1

A name of a class, object, variable or method

Front 2

Which five rules apply to an identifier?

Back 2

1. Must start with a letter, currency character ($) or connecting character (_), but NOT with a number
2. After the first character can contain letters, currency characters, connecting characters or numbers
3. There is no limit to the number of characters
4. Can't use a java keyword
5. Is case-sensitive

Front 3

Which java keywords do you know?

Back 3

abstract, boolean, break, byte, case, catch, char, class, const, continue, default, do, double, else, extends, final, finally, float, for, goto, if, implements, import, instanceof, int, interface, long, native, new, package, private, protected, public, return, short, static, strictfp, super, switch, synchronized, this, throw, throws, transient, try, void, volatile, while, assert, enum

Front 4

What's the naming convention for a class or interface?

Back 4

Starts with a capital letter and capitalizes every next word (e.g. BufferedReader)

Front 5

What's the naming convention for a method?

Back 5

Start with a lowercase letter and capitalizes every next word (e.g. readLine)

Front 6

What's the naming convention for a variable?

Back 6

Start with a lowercase letter and capitalizes every next word. Sun recommends keeping the names short. Example: readAheadLimit

Front 7

What's the naming convention for a constant?

Back 7

They're in all uppercase letters, with an underscore between seperate words: AUTO_RESIZE_OFF

Front 8

What are java beans?

Back 8

Java beans are classes that contain properties and methods named in a certain way so that third party tools like editors and frameworks can assist in using these classes.

Front 9

What are the java bean property naming rules?

Back 9

A property is usually a private instance variable (but doesn't have to be). This private instance variable is named using the naming convention for a variable.

A property will always be get and set through public method, and not directly using the variable. When you want to get a property there's two options:
1. public PropertyType getPropertyName()
2. public boolean isPropertyName()
2) only applies to boolean typed properties. 1) applies to both boolean typed properties and the rest.

So when you have a private instance variable: private boolean ready = false;
You use either: public boolean getReady() or public boolean isReady()
When you have a variable: private String name = "Name";
You use: public String getName()

When you want to set a property there's only one option:
1. public void setPropertyName(PropertyType propertyName)
So when you have a private instance variable: private String name = "Name;
You use: public void setName(String name)

Front 10

What are the java bean event naming rules?

Back 10

An event is used to notify components when something important happens. An event is listened to by listeners. A class can fire an event that needs to be listened to. This class contains two public methods:
1. A public method to add a listener as a listener for this event. An example: public void public void addActionListener(ActionListener m)
The method starts with 'add', then the type starting with an uppercase letter. The method has one argument of the type that was used in the method name.
2. A method to remove a listener as a listener for the event. An example:
public void removeActionListener(ActionListener m). The same naming rule as in 1) applies to 'remove'.
Listener methods must end with 'Listener'.

Front 11

What are the 8 rules associated with declaring classes, import statements and package statements in a source file?

Back 11

1. Only one public class per file
2. Comments can be at the beginning or the end of a line
3. If there is a public class, the name of the file must correspond with this name (Example: class BufferedReader will be in file BufferedReader.java)
4. If a class is part of a package, the package name must be the first line in the file
5. If there are imports, the imports must go between the package and the first class declaration. If there isn't a package specified, the imports go before everything else.
6. import and package statement apply to all classes specified in the file
7. A file can contain several non public classes
8. A file containing no public classes can have any name.

Front 12

What is the minimum class declaration?

Back 12

class MyClass {}

Front 13

What are the types of modifiers that can be applied to a class?

Back 13

Access modifiers and non-access modifiers

Front 14

What access modifiers are there?

Back 14

public, protected, private

Front 15

What non-access modifiers are there?

Back 15

strictfp, final, abstract

Front 16

How many access controls are there?

Back 16

Four: default, private, public, protected

Front 17

How many access modifiers are there?

Back 17

Three: private, public, protected

Front 18

What does 'having access' to a class mean?

Back 18

1. You can create an instance of the class
2. You can extend it
3. You can access certain methods and variables, depending on the access control of those methods and variables.

Front 19

What access modifier does a default class have?

Back 19

None, there is no access modifier for the default access control.

Front 20

What does default access control mean?

Back 20

You can see it as package level access. A class with default access can only be seen by classes in the same package.

Front 21

What does the 'public' access modifier do to a class?

Back 21

All classes are allowed to access that class. But only when this class has been imported using the import statement or is in the same package.

Front 22

What does the 'strictfp' modifier do to a class?

Back 22

This turns on strict floating point processing which is not platform dependent, in contrast with the default floating point processing.

Front 23

What does the 'final' modifier do to a class?

Back 23

This class can not be subclassed, so no other class can ever extend this class. Final was invented for safety/security to guarantee a certain behavior.

Front 24

What does the 'abstract' modifier do to a class?

Back 24

An abstract class can never be instantiated. It needs to be extended by a subclass first, before it's behavior can be used.

Front 25

How do you define an abstract method?

Back 25

public abstract void myMethod();

Pay particular attention to the semicolon ; at the end of the line instead of the curly brace {

Front 26

Will a class that is marked with abstract and final compile or not? Why?

Back 26

This will not compile. An abstract class must be subclassed, where a final class cannot be subclassed. This is a contradiction, resulting in a compile error.

Front 27

What are the 9 rules about interfaces?

Back 27

1. All interface methods are implicitly abstract and public.
2. All variables in an interface must be public, abstract and final. Interfaces can only declare constants.
3. Interface methods must not be static
4. Interface methods cannot be marked final, strictft or native
5. An interface can extends one or more interfaces
6. An interface can't extend anything other than an interface
7. An interface can't implement another interface or class
8. An interface must be declared with the word 'interface'
9. Interface types can be used polymorphically

Front 28

What is the access level of an interface?

Back 28

It is defined as default when you haven't specified anything. All methods of an interface are defined as public and abstract when you haven't specified anything.

Front 29

Is it allowed to have the following method definition in an interface?
protected void myMethod();

Back 29

No it isn't. Methods in an interface must be public.

Front 30

How do you define a constant in an interface?

Back 30

interface Writable {
public static final int LEFT_TO_RIGHT = 1;
}

You could also have used:
interface Writable {
int LEFT_TO_RIGHT = 1;
}

This means the same (the compiler adds public static final by itself internally)

Front 31

Is the following interface variable declaration allowed or not?

public static int x = 1;

Back 31

Yes, it is. But it's also final, as all interface variables are:
public static final

Front 32

What are the two types of members a class can have?

Back 32

1. Methods
2. Variables

Front 33

Is it possible to define a class to have protected access, like so:

protected class MyClass {}

Back 33

No, a class can only have public or default access, as in:

public class MyClass {}

or:

class MyClass{}

Front 34

What access levels can members have?

Back 34

1. protected
2. default
3. public
4. private

Front 35

What are the three ways to access a method?

Back 35

1. Invoking a method in the same class
2. Invoking a method using a reference of the class
3. Invoking an inherited method

Front 36

In what ways can a public method be invoked?

Back 36

1. Invoking a method in the same class
2. Invoking a method using a reference of the class
3. Invoking an inherited method

Front 37

In what ways can a private method be invoked?

Back 37

Only by invoking a method in the same class
The method can't be invoked by an extending class, and also can't be invoked using a reference of the class

Front 38

In what ways can a protected method be invoked?

Back 38

1. A protected method can be invoked in the same class
2. A protected method can't be invoked by a reference to the class
3. A protected method can be invoked from extending classes

Front 39

In what ways can a default method be invoked?

Back 39

A default method can be invoked:
1. From the same class
2. From any class in the same package
3. From a subclass in the same package

A default method can't be invoked:
1. From a subclass outside the package
2. From any non-subclass outside the package