java 编程笔记Word下载.docx

java 编程笔记Word下载.docx

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System.out.println（"

Thisisthefirstlesson"

）;

//printlnispartofAPI

}

}

HOWTOCOMPILEANDRUNJAVAFILES:

JavaCompiler:

javacFrstProg.java（createsFrstProg.class）

JavaInterpreter:

javaFrstProg（executesFrstProg.class）

Output:

Thisisthefirstlesson

-Comments//…or/*…*/or/**…*/

-Blocks{…}

-Methods

-mainmethod（alwayspublicstaticvoid）

-Identifiers（UpperCase,LowerCase,_,$,Digits）cannotstartwithdigit

casesensitive（TOTAL,Total,total）

-Consistencyinnaming（BeginningLowercase=>

methodsandidentifiers

BeginningUppercase=>

classes

AllUppercase=>

constants

-printandprintlnmethods

-commandlinearguments（mainmethod）

-objectorientedprogramming（classes,objects,inheritance,etc.）

//Turkey.javaFile

classTurkey

System.out.print（"

Theinternational"

+"

dialingcode"

forTurkeyis"

+90）;

//NameTag.javaFile

classNameTag

Hello!

Mynameis"

+args[0]）;

javacNameTag.java（compile）

javaNameTagXXX（run）

MynameisXXX（output）

Toimportapackage:

importpackage.class;

Or:

importpackage.*;

JAVAAPI（ApplicationProgrammingInterface）

View:

Download:

Packages

java.appletcreatesprograms（applets）thatareeasilytransportedacross

theweb.

java.awt（AbstractWindowingToolkit）Drawgraphicsandcreate

graphicaluserinterfaces.

java.ioperformawidevarietyofI/Ofunctions.

java.langgeneralsupport.Itisautomaticallyimported.

java.mathforhighprecisioncalculations.

communicateacrossanetwork.

java.rmi（RemoteMethodInvocation）createprogramsthatcanbe

distributedacrossmultiplecomputers.

java.sqlinteractwithdatabases.

java.textformattextforoutput.

java.utilgeneralutilities.

PRIMITIVEDATATYPES:

byte8bits-128127

short16bits-3276832767

int32bits-2billion2billion

long64bits-10191019

Floatingpoint:

float32bits

double64bits

Others:

char16bits65536Unicodecharacters

booleanfalsetrue

void

WRAPPERCLASSES:

Classesdeclaredinpackagejava.lang:

ByteFloatCharacterBooleanVoid

ShortDouble

Integer

Long

OPERATORS:

Unary:

+-

Binary:

*/%Multiplication,division,remainder

+-Addition,subtraction

+Stringconcatenation

=Assignment

+=-=*=/=%=

count++returncountandthenadd1

++countadd1andthenreturncount

count--returncountandthensubtract1

--countsubtract1andthenreturncount

!

Logicalnot^Bitwisexor==!

=

&

Logicaland&

Bitwiseand>

<

||Logicalor|Bitwiseor>

=<

CODITIONSANDLOOPS:

condition?

expression1:

expression2

example:

intlarger=（num1>

num2）?

num1:

num2;

if（condition）switch（expression）{

Statement1casevalue1:

elseStatement-list1;

break;

Statement2casevalue2:

Statement-list2;

….

default:

Statement-list3;

}

while（condition）doStatementfor（init;

cond;

incr）

Statement;

while（condition）;

continuebreakreturn

INSTANTIATIONANDREFERENCES

classCarExample

{

inttotal=25;

intaverage;

average=20;

//CarClassshouldbedeclared

CarClassmyCar=newCarClass（）;

CarClassyourCar;

yourCar=newCarClass（）;

//Tocallamethoduse"

."

myCar.speed（50）;

yourCar.speed（80）;

Mycarcost$"

+myCar.cost（））;

classCarClass

int_speed;

int_cost;

CarClass（）

_speed=0;

_cost=2500;

publicvoidspeed（intspeed）

_speed=speed;

publicintcost（）

return_cost;

GARBAGECOLLECTION

Objectsaredeletedwhentherearenomorereferencestothem.Thereisapossibility

tohavetheSystemrunthegarbagecollectorupondemandusingtheSystem.gc（）

method.

Callingthegc（）methodsuggeststhattheJavaVirtualMachineexpendefforttoward

recyclingunusedobjectsinordertomakethememorytheycurrentlyoccupyavailable

forquickreuse.Whencontrolreturnsfromthemethodcall,theJavaVirtualMachine

hasmadeabestefforttoreclaimspacefromalldiscardedobjects.

Ifweaddtheline:

CarClassmomCar=myCar;

wegetthefollowingdrawing:

Toreducethenumberofreferencestoanobject,

W