IT計算機 第四單元

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第四罩元

宣告、初始化和使用燮數(shù)

FundamentalsoftheJavan，ProgrammingLanguage

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軍元概

?罩元目檄

-阜雪建數(shù)的使用方法典定羲燮數(shù)的言吾法

-列出Java程式言吾言的八彳固基本型別

-根獴Java程式言吾言的指醇方金十和音吾法規(guī)即來宣告、初始

化及使用燮數(shù)典常數(shù)

-使用55算子(operator)來更改燮數(shù)值

-使用晉升(promotion)典型別醇換(typecasting)

FundamentalsoftheJavan,ProgrammingLanguageModule4,slide2of36

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擘曾燮數(shù)的使用和言吾法

翱列:

1publicclassShirt{

2

3publicintshirtID=0;//IS衫的ID

4publicStringdescription=''-descriptionrequired-";//

5

6//彥真色代礁卷R4工色，B=盛色，G/景色，U=未^定

7publiccharcolorCode='U';

8

9publicdoubleprice=0.0;//所有勰衫的fO殳^格

10

11publicintquantityInStock=0;//所有勰衫的JO殳數(shù)量

12

13//道方法印出項目的所有值

14publicvoiddisplayShirtlnformation(){

15

16System,out.printin(''ShirtID:''+shirtID);

17System,out.printin(''Shirtdescription:"+description);

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18System,out.printin(''ColorCode:''+colorCode);

19System,out.printin(''Shirtprice:''+price);

20System,out.printin(''Quantityinstock:''+quantity工nStock);

21

22}//display方法的結(jié)尾

23}//類直別的結(jié)尾

FundamentalsoftheJavaProgrammingLanguageModule4,slide4of36

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燮數(shù)的使用

?物件^醴中唯一的資料

?指派一彳固燮數(shù)值幺合其他燮數(shù)

?在數(shù)擘表示式中用來代表數(shù)值

?在簧幕中印出燮數(shù)值

?侑者存參考至其他物件

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燮數(shù)的宣告典初始化

?言吾法（腐性或燮數(shù)）：

[modifiers]typeidentifier=[value];

?^法（11域燮數(shù)）：

typeidentifier;

?吉吾法（11域燮數(shù)）：

typeidentifier=[value];

?蒯列：

publicintshirtID=0;

publicStringdescription="-descriptionrequired-";

publiccharcolorCode='Uz;

publicdoubleprice=0.0;

publicintquantitylnStock=0;

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描述基本資料型別

?整數(shù)型別(byte>short>int和long)

?浮黑占數(shù)型別(float和double)

?字元型別(char)

?暹申苴型別(boolean)

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整數(shù)型別

(K合法的字面字

型別是度如國(1itcralvalue)

靶例

byte8bits-2?到2--1（-128至U127,2

共256他可能的值）-114

short16bits-2”到26-1（-32,768到32,767,2

or65,535《固可能的值）-32699

int32bits-2”到2^-1（-2,147,483,648到2

2,147,483,647共147,334,778

4,294,967,296他可能的值）

long64bits-2。到26J-12

（-9,223,372,036854,775,808到-2,036,854,775,808L

9,223,372,036854,775,807,共IL

18,446,744,073,709,551,616

他可能的值）

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整數(shù)基本型別

publicintshirtID=0;//勰衫JIBS的ID

publicintquantityInStock=0;//所有勰衫的數(shù)量

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浮黠數(shù)基本型別

型別浮黠艮度合法的字面字，literalvalue例

float32bits99F

-327,456,99.01F

4.2E6F（工程襟IB投

4.2*106）

double64bits-1111

2.1E12

999,701,327,456,2。。。

publicdoubleprice=0.0;//所有勰衫的^格

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文字基本型別

?唯一的資料型別卷char

?用央侑者存16bits的罩一字元，如'y，字元

-輪例：

publiccharcolorCode='U';

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暹it基本型別

?唯一^的資料型月ll^bool一an

?只能用來侑者存tru一或falsa

?用來信者存建算式的建算結(jié)果卷tru一或falsa

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燮數(shù)命名

?命名規(guī)劃：

-燮數(shù)^別字必須以大嘉或小嘉字母、底^（_）或金菱字

符虢（$）作卷^豆真字母。

-燮數(shù)言戢別字不要使用檄粘符虢、空白、破折虢或任何

Java程式言吾言的展融建字。

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燮數(shù)命名

?命名型即：

-以小嘉字母卷每他燮數(shù)的^豆尾隨彳友的罩字就以大嘉

字母回如：myVariabl一。

-it攆可以落助言刖意，加者殳升可以1?使用者了解此燮數(shù)

使用目的的建數(shù)名。

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指派一彳固數(shù)值

?鸛列:

price=12.99;

?IS例(boolean)：

booleanisOpen=false;

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在一行程式中宣告典初始化燮數(shù)

?吉吾法：

typeidentifier=value[,identifier=value];

?翱列：

doubleprice=0.0,wholesalePrice=0.0;

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其他宣告典初始化燮數(shù)的方法

?指派字面字(literal)值：

intID=0;

floatpi=3.14F;

charmyChar='G';

booleanisOpen=false;

?指派一彳固建數(shù)值幺合另一彳固燮數(shù)：

intID=0;

intsalelD=ID;

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其他宣告典初始化燮數(shù)的方法

?揩算式的結(jié)果指派給整數(shù)、浮黠數(shù)或布林建數(shù)

floatnumberOrdered=908.5F;

floatcasePrice=19.99F;

floatprice=(casePrice*numberOrdered);

inthour=12;

booleanisOpen=(hour>8);

?指派方法呼叫的回停值幺合建數(shù)

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常數(shù)

?燮數(shù)（可更改）：

doublesalesTax=6.25;

?常數(shù)（不可更改）：

finaldoubleSALES_TAX=6.25;

?命名型即一常數(shù)全部的字母都卷大癮加使用底^

（）來分可句。

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信者存於言己tfrIB內(nèi)的基本資料型別典常數(shù)

Variablededaredgectewith

insideofamethodattributevariables

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幺束曾一：在程式中使用基本資料型別建數(shù)

?目檄

?步驟

?Bttt

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檄^算子

用途算子初列

加法+sum=numl+num2

如果numl等於10、num2

等於2,更Jsum等於12。

減法一diff=numl-num2

如果numl等於10、num2

等於2,邱Jdiff等於8。

乘法*prod=numl*num2

如果numl等於10、num2

等於2,用Jprod等於20。

除法/quot=numl/num2除法is算畬回傅一他

如果numl等於10、num2整數(shù)值（非模數(shù)）

等於2,即Jquot等於5。

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模數(shù)%mod=numl%num2模數(shù)是言十算第一他

如果numl等於31、num2數(shù)除以第二彳固數(shù)所

等於6,邱Jmoci等於1。得到的繪數(shù)。

典第

相同

FundamentalsoftheJavan,ProgrammingLanguageModule4,slide23of36

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遮增典遮澗算子

?晨的表示方式:

age=age+1

?短的表示方式:

建算子用途蒯列

++前置遮增inti=6;

(++variable)intj=++i;

i等於7,j等於7

彳爰置遮增inti=6;i在遽增之前

(variabl一++)intj=i++;就指定區(qū)合jo

i等於7,j等於6所以j仍等於

6o

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一前置遽減int1=6;

(--variable^)intj=--i;

i等於5,j等於5

彳爰置遮減inti=6;i在遽減之前

(variable--)intj=i--;就指定幺合jo

i等於5,j等於6所以j仍等於6。

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it增輿遮減il算子（++輿一）

翱列：

intcount=15;

inta,b,c,d;

a=count++;

b=count;

c=++count;

d=count;

System,out.printIn(a+''+b+''+c+''+d);

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算子的侵先/慢序

?建算子侵先順序的規(guī)即

1.有一舉寸II括弧的建算子

2.遮增及遮減建算子

3.乘法典除法建算子是由左而右做言十算

4.加法輿減法建算子是由左而右做言十算

?需要建算子侵先順序的靶例：

c=25-5*4/2-10+4;

答案是34或9呢？

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使用IB括弧

竄創(chuàng)列：

c=(((25-5)*4)/(2-10))+4;

c=((20*4)/(2-10))+4;

c=(80/(2-10))+4;

c=(80/-8)+4;

c=-10+4;

c=-6;

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晉升典型別醇換

?冏愚

intnuml=53;//32bits言己t意醴來信者存值

intnum2=47;//32bits言己t意艘來信者存值

bytenum3;//fl留8bits言己首亶

num3=(numl+num2);//畬造成褊群金昔

?解法：

intnuml=53;

intnum2=47;

longnum3;

num3=(numl+num2);

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晉升

?自勤彝生的晉升：

-如果你指派一彳固較小型別的燮數(shù)幺合一彳固較大型別的建

數(shù)畤

-如果你指派一彳固整數(shù)型別的燮數(shù)幺合一彳固浮黑占數(shù)型別的

?自勤褻生晉升的靶例：

longbig=6;

intsmall=99L;

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型別斡換

?吉吾法：

identifier=(target_type)value

intnuml=53;//32bits言己t意艘來存放值

intnum2=47;//32bits言己t意艘來存放值

bytenum3;//fl留8bits言己t意骨亶

num3=(numl+num2);//與芟生褊言翳昔

?解法：

intnuml=53;//32bits言己t意艘來存放值

intnum2=47;//32bits言己驚艘來存放值

bytenum3;//fl留8bits言己首亶

num3=(byte)(numl+num2);//沒有資料ifi失

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型別斡換

輪例:

intmylnt;

longmyLong=99L;

mylnt=(int)(myLong);//沒有資料遺失，只有零被刪除

//更大的數(shù)目招畬造成資料遺失

//失

intmylnt;

longmyLong=123987654321L;

mylnt=(int)(myLong);//數(shù)目曾■被截掉

Fundamentalsofthe