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SCJP > Chapter 1 - Declarations and Access Control > Flashcards

Chapter 1 - Declarations and Access Control Flashcards

To pass the SCJP 6 exam

1
Q

Access Modifiers Members can use

A

public
protected
default
private

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2
Q

Access Modifiers Classes can use

A

default

public

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3
Q

Class

A

A template that describes the kinds of state and behavior that objects of this type support

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4
Q

Object

A

When JVM encounters new keyword, make an instance of that class. Object will have its own state, and access to all behaviors defined by its class.

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5
Q

State

A

Each object has its own unique set of instance variables as defined by the class. All instance variables make up the objects state

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6
Q

Inheritance

A

Code in one class can be reused in other class. Superclasses are extended to more specific sub classes. Subclass inherits accessible instance variables and methods.

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7
Q

Interface

A

100-percent abstract superclass that identified the methods a subclass must support, but not how they must be supported.

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8
Q

Legal identifiers

A
  1. start with a letter, $, or connecting character like a _. Identifiers CANNOT start with a number
  2. after 1st character, can contain letters, $, connecting characters or numbers
  3. no limit to # of characters
  4. cant use JAVA keywords
  5. Identifiers are CASE sensitive
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9
Q

Classes and interfaces

A

First letter should be Capitalized, if more than 1 word, use camelcase.

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10
Q

Methods

A

First letter should be lowercase, then normal camelCase

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11
Q

Variables

A

start with lowercase, use camelCase

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12
Q

CONSTANTS

A

UPPER_CASE. use underscores for more than 1 word.

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13
Q

JavaBeans

A

Java classes that have properties. Properties are private instance variables only accessible by getter and setter methods

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14
Q

JavaBeans Naming Rules #1

A

If property is NOT boolean, methods prefix must be get, example getSize()

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15
Q

JavaBeans Naming Rules #2

A

If property is boolean, the getter method is get or is. For example getStopped() or isStopped()

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16
Q

JavaBeans Naming Rules #3

A

Setter method must prefex set, example setSize()

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17
Q

JavaBeans Naming Rules #3

A

Setter methods must be marked public, with void return type

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18
Q

JavaBeans Naming Rules #4

A

Getter methods must be marked public, take no arguments, and have a return type that matches the argument type of setter method for that property

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19
Q

JavaBean Listener Naming Rules #1

A

Listener methods names used to register a listener, must use the prefix add, followed by listener type: addActionListener()

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20
Q

JavaBean Listener Naming Rules #2

A

Listener methods used to remove a listener must use the prefix remove

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21
Q

JavaBean Listener Naming Rules #3

A

Listener method names must end with the word “Listener”

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22
Q

Source File Declaration Rules #1

A

There can be only one public class per source code file

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23
Q

Source File Declaration Rules #2

A

Comments can appear at the beginning or end of any line in the source code

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24
Q

Source File Declaration Rules #3

A

If there is a public class in a file, the name of the file must match the name of the public class. Example: public class Dog { } must be in source file as Dog.java

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25
Q

Source File Declaration Rules #3

A

If class is part of package, the package statement must be the first line in source file, before any import statements

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26
Q

Source File Declaration Rules #3

A

If there are import statements, they must go between the package statement and the class declaration. If NO package statement, import statements MUST be first line of source

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27
Q

Source File Declaration Rules #4

A

import and package statements apply to all classes within a source code file.

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28
Q

Source File Declaration Rules #5

A

A file can have more than one nonpublic class

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29
Q

Source File Declaration Rules #6

A

Files with no public classes can have a name that does not match any of the classes in the file.

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30
Q

Modifiers fall into two categories

A

Access modifiers: public, protected, private

Non-access modifiers: strictfp, final, and abstract

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31
Q

Class Access - 3 things

A

When code has access to another class:

  1. Create an instance of class
  2. Extend class
  3. Access certain accessable methods and variables
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32
Q

Default Access

A

Class has no modifier preceding it in the declaration. Think of it as package-level access. Classes with default can only be seen by classes within same package.

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33
Q

Public Access

A

A class declared as public gives all classes from all packages access to the public class.If public class you are accessing is in different package, must import the public class.

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34
Q

Can a class be marked as final and abstract

A

NO

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35
Q

Final Class

A

final class means the class can’t be subclassed. Guarantees none of the methods in the class will ever be overridden

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36
Q

Abstract class

A

can NEVER be instantiated. Methods in abstract class end in semicolon rather than curly pair brace {}. If a single method is marked as abstract, the WHOLE class must be declared as abstract

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37
Q

Interface

A

declares what a class can do, without saying anything about HOW the class will do it.

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38
Q

Interface

A

implicitly public and abstract

must NOT be marked as static

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39
Q

Interface

A

all variables in interface must be public, static, and final. They can only declare CONSTANTS, not instance variables.

40
Q

Interface legal declarations

A

public abstract interface Rollable { } //abstract redundant

public interface Rollable { }

41
Q

Interface method modifiers

A

public and abstract modifiers are redundant but acceptable.

42
Q

Interface constants

A

they must be public, static, and final, but done have to be declared that way. You CANNOT change the value of a interface CONSTANT!

43
Q

Interface constants

A

any combination of LEGAL modifiers is OK, as is using no modifiers at all.

44
Q

Interface constants

A

can NEVER be given a value by the implementing or any other class.

45
Q

Subclass

A

if a subclass inherits a member, it’s exactly as if the subclass actually declared the member itself

46
Q

Private Members

A

Members marked private can’t be accessed by code in any class other than the class in which the private member was declared.

47
Q

Private Members

A

you can declare a matching method in a subclass the same as the superclass marked private and its just as if the superclass private method does NOT exist.

48
Q

Can a private method be overridden by a subclass?

A

Technically NO. CAREFUL. Subclass method with same name as private superclass method makes it look and feel as if overwritten.

49
Q

Protected and Default Methods

A 
default member may be accessed only if the class accessing it is in the same package
protected members: may be accessed by inheritance even if subclass is different package
50
Q

Protected and Default methods

A

behavior differs only when talking about subclasses

51
Q

Protected Methods

A

Protected: accessible to all other classes inside package and inheritable by any subclasses outside the package

52
Q

Protected Method behavior once a subclass has inherited it

A

The member become PRIVATE to any code outside the subclass, with exception of subclasses of subclass.

53
Q

Final Method

A

Final keyword prevents a method from being overridden in a subclass.

54
Q

Final Arguments

A

Method arguments are essentially the same as variable declarations that appear in parenthesis.If arg defines var as final, it cannot be modified in the method.

55
Q

Abstract Methods

A

A method that has been declared, but not implemented; has NO functional code. Ends with a semi colon instead of a curly brace.

56
Q

Abstract Methods in Public class

A

Will NOT compile if even one method is defined as abstract in a class. You can have abstract class with no abstract methods.

57
Q

Abstract Method subclass inheritance

A

The first concrete subclass of an abstract class MUST implement all abstract methods of the superclass, unless the subclass is ALSO abstract.

58
Q

Methods can never be marked as

A

abstract and final, or both abstract and private…. it just would’t make SENSE!

59
Q

Private Methods

A

cannot be overridden, so they CANNOT be marked abstract.

60
Q

Abstract Method

A

can never be combined with the static modifier

61
Q

Synchronized Modifier

A

method can only be accessed by one thread at a time. Can ONLY be applied to methods,NEVER variables nor classes.

62
Q

Native Methods

A

method is implemented in platform dependent code like C. Must end with semicolon indicating there is no implementation.

63
Q

StrictFP Methods (Floating point)

A

can declare individual methods and or classes as strictfp, but NEVER variables.

64
Q

Constructor

A

Every time you make a new object, at least one constructor is invoked

65
Q

Constructor

A

Must have the same name as the class in which they are declared

66
Q

Constructors

A

Can’t be marked static, final or abstract

67
Q

Primitives

A

Eight types, char, boolean, byte, short, int, long, double, or float. Once declared a primative type can never be changed.

68
Q

Reference Variable

A

Declared to be a specific type, and that type can never change.

69
Q

Primitive sequence from small to big

A

Byte, short, int, long, double, float

70
Q

Primitive number types are all signed

A

That effects their ranges… First bit: 0=positive, 1=negative

71
Q

Range of numeric primatives

A 
byte 8
short 16
int 32
long 64
float 32
double 64
72
Q

char

A

contains a single, 16 bit Unicode character

73
Q

instance variables

A

defined inside the class, but outside of any method, and only initialized when class is instantiated

74
Q

instance variables

A

fields that belong to each UNIQUE object

75
Q

instance variables

A

can be marked final

cannot be marked abstract, synchronized, strictfp, native or static

76
Q

local variables

A

variables declared within a method

77
Q

local variables

A

always on stack, not on the heap

78
Q

local variables

A

must be initialized before they are used

79
Q

array declarations

A

arrays are OBJECTS that store multiple values of the SAME type.

80
Q

arrays

A

ALWAYS objects on the HEAP

81
Q

array of Primatives

A

declared by stating the type of elements the array will hold, followed by square brackets on either side of the identifier:
int[] key;
int key [];

82
Q

array of Objects

A

Thread[] threads; // Recommended

Thread threads []; // legal but less readable

83
Q

Multidimensional arrays

A

String[] [] [] occupantName; // 3 dim array

String[] managername[]; // 2 dim array

84
Q

array declaration

A

never legal to include size of array in your declaration.
int [5] scores ; // illegal
JVM doesn’t allocate space until you actually instantiate the array object.

85
Q

Final Variables

A

once initialized to value; CANNOT reinitialize or change it

86
Q

Final Object Reference Variable

A

once assigned can never refer to a different object. The data within object can be modified, but the reference variable cannot.

87
Q

Burn this in

A

there are no final objects, only final references

88
Q

Transient Variables

A

tell JVM to skip the variable when you attempt to serialize it.

89
Q

Volatile Variables

A

can only be applied to instance variables.

90
Q

Can mark as Static

A

methods
variables
a class nested within another class, but not within a method
Initialization blocks

91
Q

static members

A

exist before you ever make a new instance of a class, and will only be ONE copy.

92
Q

enums

A

cannot declare them in a method

93
Q

enums

A 
semicolon on declaration is optional
enum CoffeeSize ( BIG, HUGE, SMALL ) ; //; not required
94
Q

enums

A

you can NEVER invoke an enum constructor directly, the enum constructor is automatically invoked.

95
Q

enums

A

you can declare more than one argument to the constuctor. as BIG(i, “A”)

SCJP (5 decks)

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