8/7/2019 Java Notas

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 1 3/12/2007

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 2 3/12/2007

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 3 3/12/2007

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 4 3/12/2007

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 5 3/12/2007

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 6 3/12/2007

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 7 3/12/2007

Car extends Vehicle means Car IS-A Vehicle.Subaru extends Car means Subaru IS-A Car.

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 8 3/12/2007

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 9 3/12/2007

Modifiers and Access Modifiers

Local Variables Variables (non-Local) Methods Classes

finalpublic

protectedprivatestatic

publicdefault

final

finalpublic

protectedprivatestatic

transient

abstractsynchronized

strictfpnative

Final

Modifiers and Access Modifiers

Modifier Class Variable Method ConstructorFree-Floating

Block

public yes yes yes yes no

protected no yes yes yes no

(default) yes yes yes yes yes

private no yes yes yes no

final yes yes yes no no

abstract yes no yes no no

static no yes yes no yes

native no no yes no no

transient no yes no no no

volatile no yes no no no

synchronizedno no yes no yes

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 10 3/12/2007

Default Values for Array Elements

Array Type Default Value

byte 0

char '\u0000'

short 0

int 0

long 0L

float 0.0F

double 0.0

Boolean false

Object reference null

Java Primitive Data Types

Type Contains Default Size Min/Max Value

boolean true or false false 1 bit N.A.N.A.

char Unicode character \u0000 16 bits, twos complement

\u0000\uFFFF

byte signed integer 0 8 bits, twos complement-2

7 2

7-1

short signed integer 0 16 bits, twos complement

-2

15 2

15-1

int signed integer 0 32 bits, twos complement

-2

31 2

31-1

long signed integer 0 64 bits, twos complement

-2

63 2

63-1

float floating-point 0.0 32 bits, IEEE 754 +/-1.40239846E-45+/-3.40282347E+38

double floating-point 0.0 64 bits, IEEE 754 +/-4.94065645841246544E-324+/-1.79769313486231570E+308

Java Escape Sequences

Escape Sequence Unicode Equivalent Meaning

\b \u0008 Backspace

\t \u0009 Horizontal tab

\n \u000a Linefeed

\f \u000c Form feed\r \u000d Carriage return

\" \u0022 Double quote

\' \u0027 Single quote

\\ \u005c Backslash

\xxx \u0000 to \u00ff The character corresponding to the octal value xxx

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 11 3/12/2007

Class Member Accessibility

Member VisibilityModifier

same class same package subclass Universe

private yes

default yes yes

protected yes yes yes

public yes yes yes yes

Class Member Accessibility

Member Visibility

Accessible to:public protected package o

defaultprivate

Same class yes yes yes yesClass in same package yes yes yes

Subclass in same package yes yes yes

Subclass in different package yes yes

Non-subclass, different package yes

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 13 3/12/2007

Java Modifiers

Modifier Used On Meaning

classThe class contains unimplemented methods and cannot beinstantiated.

interface

All interfaces are abstract. The modifier is optional in interface

declarations.abstract

methodNo body is provided for the method (it is provided by a subclass).The signature is followed by a semicolon. The enclosing classmust also be abstract.

class The class may not be subclassed.

fieldThe field may not have its value changed (compiler mayprecompute expressions).

method The method may not be overridden (compiler may optimize).final

variableJava 1.1 and later: the local variable or method or exceptionparameter may not have its value changed.

native methodThe method is implemented in C, or in some other platform-dependent way. No body is provided; the signature is followed by a

semicolon.class A non-public class is accessible only in its package

interface A non-public interface is accessible only in its packagenone (package)

memberA member that is not private, protected, or public has packagevisiblity and is accessible only within its package.

private member The member is only accessible within the class that defines it.

protected memberThe member is only accessible within the package in which it isdefined, and within subclasses.

class The class is accessible anywhere its package is.

interface The interface is accessible anywhere its package is.public

member The member is accessible anywhere its class is.

class In Java 1.1, a class delared static is a toplevel class, not an innerclass.

fieldA static field is a "class field." There is only one instance of thefield, regardless of the number of class instances created. It maybe accessed through the class name.

initializerThe intializer is run when the class is loaded, rather than when aninstance is created.

static

methodA static method is a "class method." It is not passed as an implicitthis object reference. It may be invoked through the class name.

synchronized method

The method makes non-atomic modifications to the class orinstance, and care must be taken to ensure that two threadscannot modify the class or instance at the same time. For a staticmethod, a lock for the class is acquired before executing the

method. For a non-static method, a lock for the specific objectinstance is acquired.

transient fieldThe field is not part of the persistent state of the object, and shouldnot be serialized with the object.

volatile fieldThe field may be accessed by unsynchronized threads, so certaincode optimizations must not be performed on it.

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Sun Certified Programmer for Java 2 Study Guide Tables and Figures

JCTV 14 3/12/2007

Strings

Consider this table showing two situations using the == operator and equals():

s1 == s2 s1.equals(s2)

AString s1 = Java;

String s2 = Java;true true

BString s = Ja;

String s1 = s + va;

String s2 = Java;

false true

In situation A, the evaluation will always return true, since there is only one Stringobject created (s1 and s2 are both pointing to the same one).

To avoid the above situation, use the new keyword so that s1 and s2 are created asdifferent objects.

In situation B, s1 and s2 are pointing to different objects, because s1 is created at

runtime.

byte intshort long

float

char

double

Legal Conversions Between Numeric Types