ng on ngu lap trinh java

8/10/2019 Ng on Ngu Lap Trinh Java

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Ngn ng lp trnh Java


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TNG QUAN TI LIU Nhng khi nim trong lp trnh hng i tng. C bn v ngn ng Java.

C bn v i tng (Objects), nhng i tng dliu n gin. Lp (Classes) v k tha (Inheritance) Giao din (Interfaces) v Packages.

Gii quyt nhng li thng gp khi vit chngtrnh.


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Bi 1: Nhng khi nim trong lptrnh hng i tng


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i tng l g? nh ngha: i tng l mt gi phn mm bao

gm nhng bin (variables) v nhng phnngthc lin quan (related methods).

Variables: lu tr trng thi (states) ca i tng. Methods: th hin nhng hnh ng (behavior)

ca i tng.

Vic ng gi ny c 2 li ch: Tnh module (Modularity).

Che giu thng tin (Information-hiding).


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Thng ip (Message) l g? Nhng i tng phn mm tng tc v giao tip

vi nhau bng cch truyn thng ip (sendingmessage).

Thng ip c 2 li ch quan trng: Mi tng tc gia cc i tng u thc hin c

ch bng cc thng ip.

Nhng i tng c th khc process, trn mykhc u c th gi/nhn thng ip cho nhau.


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Lp (class) l g? Lp l mt m t v nhng bin, phng thc cho

tt c nhng i tng thuc lp .

S khc nhau gia i tng vi lp: i tng l mt th hin (instance) c th ca mt

lp. Thut ng i tng (object) nhiu khi c dng

ch c lp (class) v nhng th hin (instance) calp.


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K tha (Inheritance) l g? Lp trnh hng i tng a thm nhng nh

ngha: lp con (subclass), lp cha (superclass), ktha (inherit), override.

Lp con k tha ton b nhng bin ca lp cha.Ngoi ra, lp con cn k tha mt s phng thcca lp cha.

Li ch ca k tha: lp con cung cp nhng phngthc chuyn bit (code reuse). Lp trnh vin c thto ra nhng lp abstract nh ngha nhngphng thc chung.


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SUMMARY Class l khun mu cho nhng i tng. Objects c to ra t class. Th no l constructor. Khi to i tng nh th no. Bin v phng thc ca lp. Bin v phng thc ca instance. Interface l mt giao thc ca nhng hnh ng.

Implement mt interface l implement tt c nhng phngthc trong interface.


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Interface l g? Trong ngn ng lp trnh Java, interface l mt kiu.

Ging vi class, interface nh ngha cc phngthc. Khc vi class, interface khng implement ccphng thc ny.

Interface c li ch: Th hin phn chung ca nhng lp khng c quan h vi

nhau.

Khai bo nhng phng thc m lp phi implement. Phi by giao din ca i tng m khng phi by lp ca

i tng. Mt cch thc hin a k tha.


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Bi 2: C bn v ngn ng Java


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Bin (Variables)


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Variables Bin l mt mc d liu c t tn. Cch khai bo mt bin: type name [= ];

//integersbyte largestByte = Byte.MAX_VALUE;

short largestShort = Short.MAX_VALUE;int largestInteger = Integer.MAX_VALUE;long largestLong = Long.MAX_VALUE;

//real numbersfloat largestFloat = Float.MAX_VALUE;double largestDouble = Double.MAX_VALUE;

//other primitive typeschar aChar = 'S';boolean aBoolean = true;


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Kiu d liu (1): PrimitivesKeyword Description Size/FormatIntegers

byte Byte-length integer 8-bit twos complement

short Short integer 16-bit twos complementint Integer 32-bit twos complement

long Long integer 64-bit twos complement

Real numbers

float Single-precision floating point 32-bit IEEE 754double Double-precision floating point 64-bit IEEE 754

Other types

char A single character 16-bit Unicode character

boolean A boolean value (true/false) true or false


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Kiu d liu (2): v dLiteral Value Kiu d liu178 int

8864L long

37.266 double

37.266D double

87.363F float

26.77e3 double

c chartrue boolean

false boolean


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Kiu d liu (3): tham chiu Arrays, classes, interfaces l kiu tham chiu (reference).

reference An object/arrayobjectName


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Tn bin Bt u l: k t, $, _. Theo sau l k t, s, $, _. Phn bit

ch hoa ch thng. Ngn ng Java yu cu: l mt nh danh hp l. Khng phi t

kha. Duy nht trong phm vi (scope) ca n. Quy c t tn: tn bin bt u l ch thng. Tn lp bt

u bng ch hoa. K t u mi t vit hoa. K t (_) thngch c dng ngn cch nhng t trong constants.


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Phm vi ca bin


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Khi to bin type variable = ;//integersbyte largestByte = Byte.MAX_VALUE;short largestShort = Short.MAX_VALUE;int largestInteger = Integer.MAX_VALUE;long largestLong = Long.MAX_VALUE;

//real numbersfloat largestFloat = Float.MAX_VALUE;

double largestDouble = Double.MAX_VALUE;

//other primitive typeschar aChar = 'S';boolean aBoolean = true;


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Bin final Ta c th khai bo bin trong bt k phm vi no l final. Gi tr

ca bin final khng th thay i c sau khi khi to. Khai bo: final type variable [= ]; V d:final int aFinalVar = 0;

final int blankFinal;

blankFinal = 0; Mi c gng thay i bin final sau khi khi to s pht sinh

li compile time.`


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Ton t (operators)


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Ton t tnh ton (Arithmetic)Operator S dng M t

+ op1 + op2 Cng; ni xu (String)

- op1op2 Tr

* op1 * op2 Nhn

/ op1 / op2 Chia

% op1 % op2 Php ly phn d ca op1 / op2

Ch vi php ton %: Dng cho c s thc. Quy tc: a % b = (du ca a) abs(a) % abs(b);V d: -5 % 3 = -2; -5 % -3 = -2; 5 % 3 = 2; 5 % -3 = 2


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Unary Arithmetic Operators

Operator S dng M t

+ +op Tr v kt qu int nu op kiu byte, short,char

- -op Tr v kt qu o du ca op


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Shortcut Arithmetic Operators

Operator S dng M t

++ op++ Tng op nn 1; tr v gi tr ca op trckhi tng

++ ++op Tng op nn 1; tr v gi tr ca op sau khitng

-- op-- Gim op i 1; tr v gi tr ca op trc khigim

-- --op Gim op i 1; tr v gi tr ca op sau khi

gim

V d 1: a = 5; b = a++ + ++a + a++; a = ?, b = ?;V d 2: a = 5; b = a-- + ++a + a++; a = ?, b = ?;V d 3: a = 2; array[a] = a = 0;


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Relational Operators

Operator S dng M t

> op1 > op2 Tr v true nu op1 ln hn op2

>= op1 >= op2 Tr v true nu op1 ln hn hoc bng op2

< op1 < op2 Tr v true nu op1 nh hn op2

=,


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Conditional Operators

Operator S dng M t

&& op1 && op2 Tr v true nu op1 v op2 true. Khng lnggi op2 nu op1 false

|| op1 || op2 Tr v true nu op1 hoc op2 true. Khnglng gi op2 nu op1 true

! !op Tr v true nu op false

& op1 & op2 Tr v true nu op1v op2 true. Lun lunlng gi op2. Thc hin bitwise AND vi 2

ton hng s.| op1 | op2 Tr v true nu op1 hoc op2 true. Lun lun

lng gi op2. Thc hin bitwise OR vi 2ton hng s.

^ op1 ^ op2 Tr v true nu op1 v op2 l khc nhau.

(XOR logic)


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Shift Operators

Operator S dng M t

op1 >> op2 Dch phi op1 op2 bits. Lp y bn bn tri

bng bit du (Signed right shift).>>> op1 >> op2 Dch phi op1 op2 bits. Lp y bn tri bng

0 (Unsigned right shift).

V d: 13 >> 1: 6; -13 >> 1: -6; -13 >>> 1: 2147483641;

V d: 1


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Bitwise Logic Operators

Operator S dng M t

& op1 & op2 AND bit. Ch p dng cho kiu integeral.

| op1 | op2 OR bit. Ch p dng cho kiu integeral.

^ op1 ^ op2 XOR bit. Ch p dng cho kiu integeral.

~ ~op Ly b bit (complement). (0->1, 1->0). Chp dng cho kiu integral.


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Assignment Operators

Operator S dng M t

= op1 = op2 Gn gi tr op2 cho op1. Tr v gi tr caop1 sau khi gn.

op= op1 op= op2 Vit tt ca op1 = op1 op op2. C mt lith: khng phi p kiu.opc th l: +, -, *, /, %, &, |, ^, ,>>>

Li th khng phi p kiu:

byte a = 2;

a = (byte)(a + 3);

Vit gn:a += 3;


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Others Operators

Operator S dng M t

?: op1 ? op2 :op3

Nu op1 true, tr v op2; ngc li tr vop3.

[] Dng choarray S dng khai bo, khi to, truy cp phn tmng.

. Dng cho itng

Truy cp variables, methods ca i tng,class.

(params) Dng trong

methods

Khai bo danh sch cc bin.

(type) (type)op p kiu

new To i tng To i tng/array mi.

instanceof op1 instanceofop2

Return true nu op1 l mt th hin ca op2.(op2 l class type, interface type, array type).


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Biu thc


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nh ngha Biu thc l mt chui cc bin, ton t, li gi phng thc

c to thnh theo ng c php ca ngn ng. Kt qu trv mt gi tr.

V d: aChar = S, The string + value,Character.isUpperCase(aChar). Trong Java th t lng gi cc ton hng trong biu thc l

duy nht: t tri -> phi. Sau php ton c thc hin datrn th t tnh ton ca ton t. V d:

1. int[] a = {4, 4}; 2. int b = 1; 3. a[b] = b = 0;Line 3 equivalent: a[1] = b = 0;


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Th t u tin ca ton tNhm Ton t

Unary ++ -- + - ! ~ (type)

Arithmetic * / %

+ -

Shift > >>>

Comparison < >= instanceof

== !=

Bitwise & ^ |

Short-circuit && ||

Condition ?:

Assignment = op=


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Cu lnh - statement


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nh ngha Cu lnh tng ng vi mt cu trong ngn ng t nhin.

Cu lnh to nn mt n v thc thi y . Nhng biu thc sau y c th to thnh cu lnh bng

cch b xung du (;) vo cui biu thc:1. Nhng biu thc gn: a = S;2. Biu thc s dng ++, --: a++;3. Nhng li gi phng thc: System.out.println(String);4. Biu thc to i tng: Integer obj = new Integer(4); Cu lnh khai bo: double aValue = 933.24; Cu lnh iu khin: for, if, while, do while, switch, return,

break, continue.


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Khi lnh (Blocks) nh ngha: l mt nhm cha 0 hoc nhiu lnh c t

trong cp {}. N c th c s dng bt k ni no m lnhn c th s dng.

V d:if(Character.isUpperCase(aChar)) {System.out.println(The upper character);System.exit(0);

}


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Cu lnh iu khin


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while, do - while

+ while () {

statement

}

Lp khi iu kin cn ng. Kim tra iu kin trc khi thc hinlnh.+ do {

statement

} while();

Lp khi iu kin cn ng. Kim tra iu kin sau khi thc hinlnh.? 1. while (i > 0) i--; 2. do i--; while (i > 0); 3. do i--; j--; while (i >

0);


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for

for (initialization; termination; increment) {

statement(s)

}

Lp v hn: for ( ; ; ) {}Ch : phn khi to (initialization) v phn bc nhy (increment)

c th cha nhiu biu thc (khai bo) ngn cch bi du (,).for (int i = 0, j = 1; i < 10; i++, j+=2) {}? for (int i = 0, long j = 1; i < 10; i++, j+=2) {}? for (int i = 0, long j = 1; ; i++, j+=2) {}


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Enhanced for

Java 1.5 cung cp lnh for m rng lp qua mng, collection(Iterable):

for (var : ) {}

V d:int[] a = {4, 3, 2, 1};

for(int i : a) { System.out.println(i); }

Collection col = new ArrayList();

Integer iobj;

for(iobj : col) { System.out.println(iobj); }


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if, if/else

Cu lnh if r nhnh da trn biu thc logic:if () { statement(s) }

Phn else c th c hoc khnng:

if () {statement(s)

}

else {

statement(s)}

?: if (aChar = A) { System.out.println(aChar); }C th dng ton t ? : thay th cu lnh if/else


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switch

Lnh r nhnh da trn biu thc dng int (byte, short, char, int;but not long) hoc kiu lit k enum(Java 1.5)

switch() {

case :

statement(s);

break;

case :

statement(s);

break;[default:

statement(s);

}


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Lnh x l exceptiontry catch finally

try {

statement(s)

} catch(exceptiontype name) {

statement(s)} finally {

statement(s)

}

C th c nhiu khi catch vi exeption type khc nhau. Khi finally lun c thc hin nu khi lnh try c thc

hin (tr khi ta dng lnh System.exit()).


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break, continue, return(branching statements)

break dng kt thc vng lp for, while, do while: break[label];

continue dng b qua vng lp hin ti: continue [label]; return thot khi phng thc v tr v gi tr (nu c): return

[];

loop1:

for(i = 0; i < 100; i++) {

for(j = 0; j < 1000; j++) {

if (j == i * 12 + 7)break loop1;

}

}


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Bi 3: C bn v i tng(Objects), nhng i tng d liun gin.


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Life Cycle ca mt i tng


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To ra i tngC 3 bc chnh: Khai bo bin tham chiu (reference): type name Khi to i tng: new class

Gi constructor ca i tng: constructor cng tn vi lp,khng c gi tr tr v.C th gp thnh mt bc:Point originOne = new Point(23, 94);

Ch : Khi nh ngha class, nu ta khng nh ngha bt kconstructor no, java compiler s to cho ta mt defaultconstructor khng c tham s, cng access modifier vi class.


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S dng i tng Tham chiu n bin ca i tng (qualified name):

objectReference.variableName

Gi phng thc ca i tng:objectReference.method([argumentList])

Access Modifier: private < default < protected < public:

+ private: this object, class only.

+ default: all classes in the same package.

+ protected: the subclasses. Java 1.5 c thm hn ch: nusubclass package khc, ch c th truy cp n protectedmembers ca i tng hin thi.

+ public: all classes.


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Thu hi nhng i tng khng cns dng

i tng khng cn c s dng khi cc tham chiu n nra khi phm vi hoc khng cn tham chiu n n:

Point pt = new Point(0, 0); pt = null;

Java t ng thu hi nhng i tng khng cn c s dnggarbage collection. Ta c th thc y garbage collection bng: System.gc() hoc

Runtime.gc().

Ta khng th khng nh c khi no mt i tng s b thu

hi.


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Character


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Static methods ca lp Character

Method Description

boolean isLetter(char ch)boolean isDigit(char ch)

Determines whether the specified char valueis a letter or a digit, respectively.

boolean isWhiteSpace(char ch)Determines whether the specified char value

is white space according to the Javaplatform.

boolean isUpperCase(char ch)boolean isLowerCase(char ch)

Determines whether the specified char valueis upper- or lowercase, respectively.

char toUpperCase(char ch)char toLowerCase(char ch)

Returns the upper- or lowercase form of thespecified char value.

toString(char ch)Returns a String object representing the

specified character value.

int digit(char ch, int radix)Returns the numeric value of the character in

the specified radix.


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String, StringBuffer, StringBuilder


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Khi no s dng String,StringBuilder, StringBuffer

String: Khi ni dung ca xu s khng thay i String objectl immutable (i tng s khng thay i sau khi khi to).

StringBuilder (Ch t Java 1.5 mi c lp ny): Khi ni dung ca

xu s thay i. Ch c 1 thread truy cp n ni dung ca xu(Not threadsafe). B li, tc nhanh. StringBuffer: Khi ni dung ca xu s thay i. C th c nhiu

thread truy cp n ni dung ca xu (threadsafe). Hn ch tc chm.

StringBuilder, StringBuffer nh ngha method append cho bt kkiu d liu no.


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To String, StringBuilder,StringBuffer

Hy tra cu trong JDK 1.5 nhng constructor ca cc lp ny.V d:String palindrome = "Dot saw I was Tod";

char[] helloArray = { 'h', 'e', 'l', 'l', 'o' };String helloString = new String(helloArray);

System.out.println(helloString);

Constructors ca StringBuilder (tng t vi StringBuffer):StringBuilder(), StringBuilder(CharSequence), StringBuilder(int),StringBuilder(String).


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di ca String, StringBuilder,StringBuffer

di: phng thc length(), tr v int l di ca xu tnhtheo s k t.

StringBuilder, StringBuffer cn c phng thc capacity(), tr v

int l ln ca b m.V d:String palindrome = "Dot saw I was Tod";

int len = palindrome.length();


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Truy cp n cc k t trong String,StringBuilder, StringBuffer

Phng thc charAt(int), v substring(int [, int]).V d:String anotherPalindrome = "Niagara. O roar again!";

char aChar = anotherPalindrome.charAt(9);


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Tm kim k t, substring trongString

Method Description

int indexOf(int)int lastIndexOf(int)

Returns the index of the first (last) occurrence of thespecified character.

int indexOf(int, int)int lastIndexOf(int, int)

Returns the index of the first (last) occurrence of thespecified character, searching forward(backward) from the specified index.

int indexOf(String)int lastIndexOf(String)

Returns the index of the first (last) occurrence of thespecified string.

int indexOf(String, int)int lastIndexOf(String, int)

Returns the index of the first (last) occurrence of thespecified string, searching forward (backward)from the specified index.

booleancontains(CharSequence)

Returns true if the string contains the specifiedcharacter sequence


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Thay th k t, substring trongString

Method Description

String replace(char,char)

Replaces all occurrences of the character specified as thefirst argument with the character specified as the secondargument. If no replacements are necessary, the originalstring object is returned.

String replaceAll(Stringregex, Stringreplacement)

Replaces each substring of this string that matches thespecified regular expression.


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So snh Strings, tng phn trongString

Method Description

boolean endsWith(String)boolean startsWith(String)boolean startsWith(String, int)

int compareTo(String)int compareToIgnoreCase(String)

boolean equals(Object)boolean equalsIgnoreCase(String)boolean contentEquals(CharSequence)

boolean regionMatches(int, String, int,int)boolean regionMatches(boolean, int,String, int, int)

boolean matches(String regex)


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Thao tc trn String

Method Description

String concat(String)

String[] split(String, int)

String[] split(String)

int - max return array size

CharSequencesubSequence(int, int)

String trim()

String toLowerCase()String toUpperCase()


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Thao tc trn StringBuilder,StringBuffer

StringBuffer append(boolean)StringBuffer append(char)StringBuffer append(char[])

StringBuffer append(char[], int, int)StringBuffer append(double)StringBuffer append(float)StringBuffer append(int)StringBuffer append(long)StringBuffer append(Object)

StringBuffer append(String)

StringBuffer delete(int, int)StringBuffer deleteCharAt(int)

StringBuffer insert(int, boolean)StringBuffer insert(int, char)StringBuffer insert(int, char[])StringBuffer insert(int, char[], int,

int)StringBuffer insert(int, double)StringBuffer insert(int, float)StringBuffer insert(int, int)StringBuffer insert(int, long)StringBuffer insert(int, Object)StringBuffer insert(int, String)

StringBuffer replace(int, int, String)void setCharAt(int, char)

StringBuffer reverse()


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Number


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Number classes


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Nhng method chung ca lpNumber

Method Description

byte byteValue()short shortValue()

int intValue()long longValue()float floatValue()double doubleValue()

Convert the value of this number object to the primitivedata types of byte, short, int, long, float, and double.

compareTo

Compare this number object to the argument. Note thatthe Number class does notimplement the Comparable

interface, but most of the subtypes implementComparable.

boolean equals(Object)Determine whether this number object is equal to the

argument. Note that the Number class does notoverride the equals method from Object..


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Mt s constant hu ch ca lp Floatv Double

Constant Description

Float.NaNDouble.NaN

Not a Number. Returned by certain methods in

the java.lang.Math class when the result isundefined for the arguments passed to themethod.

Float.NEGATIVE_INFINITYDouble.NEGATIVE_INFINITY

The negative infinity value for a float or a double.

Float.POSITIVE_INFINITYDouble.POSITIVE_INFINITY

The positive infinity value for a float or a double.


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Chuyn t String sang Number

S dng phng thc static ca wrapper class (Byte, Integer,Double, Float, Long, Short): valueOfreturn wrapper type.

V d:

float f = Float.valueOf(9.3).floatValue();double d = Double.valueOf(9.3e2).doubleValue();


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Chuyn t Number sang String

C 3 cch:

Dng ton t gp xu vi xu . Dng phng thc static String.valueOf(primitive).

Dng phng thc static toString(primitive) ca cc lp: Byte,Short, Integer, Long, Float, Double.V d:int i;

String s1 = + i;String s2 = String.valueOf(i);

String s3 = Integer.toString(i);


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Nhng php ton s hc nng cao

Method of Mathclass

Description

double abs(double)float abs(float)

int abs(int)long abs(long)

Tr v gi tr tuyt i

double ceil(double) Tr v gi tr nguyn ln nht nh hn i s

double floor(double) Tr v gi tr nguyn nh nht ln hn i s

double rint(double)Tr v gi tr nguyn gn vi i s nht kiu

double (rintround integer)

long round(double)int round(float)

Tr v gi tr lm trn ca i s kiu long, int


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Arrays


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Tng qut v Array

Array l mt cu trc lu tr nhiu gi tr ca cng mt kiu. di ca array c thit lp khi array c to ra. Sau khito ra, di ca array khng thay i c.


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To v s dng Arrays (1)

Khai bo bin tham chiu n array: elementType[] name;int[] anArray; //Khng khai bo kch thc ca array.boolean[] anArrayOfBooleans;

Object[] anArrayOfObjects;String[] anArrayOfStrings;

To (cp pht) array: new elementType[size];anArray = new int[10];

Array Initializers: shortcut syntax to v thit lp gi tr choarray: {list of values};

boolean[] answers = {true, false, true, true, false};


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To v s dng Arrays (2)

Truy cp n phn t ca Array: arrayname[index]for(int i=0; i


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Array ca Objects

Array c th cha kiu tham chiu (reference) cng nh kiu cs (primitive). Vic to, khi to u ging nhau:

String[] anArray = {String One, String Two, String Three};

Object[] anObjArray = { String, new Integer(10), new Byte(2)};


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Array ca Arrays (1)

Array c th cha nhng phn t l Array. Khi , cp phtArray bng new, ch s cui cng khng c c mt.

String[][] anArray = { {One, Two}, {Three, Four}};

int[][] aMatrix = new int[4][]; aMatrix[1] = new int[3]; aMatrix[2]= new int[5];


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Copy Array

copy array, ta dng phng thc static ca lp System:public static void arraycopy(Object source, int srcIndex, Object

dest, int destIndex, int length).


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Array ca Arrays (2)


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Bi 4: Lp (Classes) v k tha(Inheritance)


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To lp


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Khai bo lpElement Function

@annotation(Optional) An annotation (sometimes called meta-

data)

public (Optional) Class is publicly accessible

abstract (Optional) Class cannot be instantiated

final (Optional) Class cannot be subclassed

classNameOfClass

Name of the class

(Optional) Comma-separated list of type variables

extends Super (Optional) Superclass of the class

implementsInterfaces

(Optional) Interfaces implemented by the class

{ ClassBody} Provides the class's functionality


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Khai bo Member Variables

Element Function

accessLevel (Optional) Access level for the variable

static (Optional) Declares a class variable

final(Optional) Indicates that the variable's value cannot

change

transient (Optional) Indicates that the variable is transient

volatile (Optional) Indicates that the variable is volatile

type name The type and name of the variable


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nh ngha Methods (1)


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nh ngha Methods (2)

Element Function

@annotation (Optional) An annotation (sometimes called meta-data)

accessLevel (Optional) Access level for the method

static (Optional) Declares a class method

(Optional) Comma-separated list of type variables.

abstract(Optional) Indicates that the method must be implementedin concrete subclasses.

final (Optional) Indicates that the method cannot be overridden

native

(Optional) Indicates that the method is implemented in

another languagesynchronized (Optional) Guarantees exclusive access to this method

returnTypemethodName

The method's return type and name

(paramList) The list of arguments to the method

throws exceptions (Optional) The exceptions thrown by the method


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nh ngha Constructors

Constructor c cng tn vi lp. Khng c kiu tr v. C hockhng c tham s.

public Stack() { }

public Stack(int size) {} Trong constructor, ta c th gi superclass constructor:

super([danh sch i s]); hoc constructor khc: this([danhsch i]). Nhng lnh ny, nu c, phi l lnh u tin trongconstructor.

T th h M th d


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Truyn tham s cho Methods,Constructors

Java truyn tham s bng gi tr: primitive type passed byvalue; cn li - passed by value of reference.

Java 1.5 cho php phng thc c th nhn mt s bt k thams (c gi l varargs).

public static Polygon polygonFrom(Point listOfPoints) {//listOfPoints kiu Point[]

}

System.out.printf(String format, Object args);


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Tr v gi tr t Methods

Lnh return .public boolean isEmpty() { return items.isEmpty(); }

Nu method khai bo kiu tr v l void, ta dng lnh return

khng c biu thc hoc l khng cn lnh return. Vi override method, kiu tr v c th l subclass ca kiu tr

v ca overrided method (covariant return type Java 1.5) chkhng cn phi ging hon ton.


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S dng t kha this

C ch khi ta cn truy cp n cc members ca lp m trongphm vi hin thi c bin trng tn:

public class HSBColor {

private int hue, saturation, brightness;public HSBColor (int hue, int saturation,

int brightness) {

this.hue = hue;

this.saturation = saturation;

this.brightness = brightness;

}

}

Ki t t b


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Kim sot truy cp n members calp

Ta s dng access modifier.class Point {

privateint x, y;

publicint getX() { return x;}}

Specifier Class Package Subclass World

private Y N N N

no specifier Y Y N N

protected Y Y Y N

public Y Y Y Y

M b i t b


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Members ca instance v membersca lp

Members ca instance: khng c t kha static. Chtruy cp c khi i tng c khi to.

Members ca lp: khai bo c t kha static. C thtruy cp trc tip qua tn lp.

class A {

public void instanceMethod() {}

public static void classMethod() {} }

A a = new A();

a.instanceMethod();a.classMethod();

A.classMethod();

Khi to members ca instance v


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Khi to members ca instance vmembers ca lp (1)

Khi to trc tip.private int i = 10;

private static int count = 0;

Khi to instance member qua constructor hocinitialization blockkhi lnh t do trong body caclass, c gi trc mi constructor:

{

i = 10;

}

Khi to members ca instance v


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Khi to members ca instance vmembers ca lp (2)

Khi to class member qua static initialization blockstatic {

count = 0;

}static initialization block c gi thc hin khi class

c np vo h thng.


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Qun l k tha


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Overriding v Hiding Methods

Mt instance method ca subclass vi cng ch k (signature)v return type vi instance method ca superclass c gi loverrides. Java 1.5 cho php kiu tr v ca override method lkiu con ca kiu tr v ca method lp cha (covariant returntype).

Instance method ch c th override bng mt instance method.Static method ch c th hide bng mt static method. Ngcli, pht sinh li compile.


92/115

Hiding Member Variables

Ta c th nh ngha mt bin trong subclass trng tn vi bintrong superclass. Khi bin trong subclass s che bin trongsuperclass. truy cp n bin trong superclass phi dng:super.variableName.


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S dng t kha super

Ta s dng t kha super truy cp n cc phng thc,bin ca lp cha: super.memberName;

public class Superclass {public boolean aVariable;public void aMethod() { aVariable = true; } }

public class Subclass extends Superclass {public boolean aVariable; //hides aVariable in Superclasspublic void aMethod() { //overrides aMethod in Superclass

aVariable = false;super.aMethod();

System.out.format("%b%n", aVariable);System.out.format("%b%n", super.aVariable);}

}


94/115

Final Class v Final Method

Ta khng th extends mt final class:public class final A {}public class B extends A {} //compile error

Ta khng th override mt final method:class A {final void finalMethod() {}

}

class B extends A {

void finalMethod() {} //compile error

}


95/115

Abstract Method v Abstract Class

Abstract method: ch c khai bo, khng c body.abstract void draw();

Abstract class: khai bo vi t kha abstract.

public abstract class Figure {} Khi mt lp c 1 phng thc l abstract (hoc cha c

implement), n buc phi khai bo l abstract. (nhng ngc lith khng ng mt lp abstract c th khng c mt phngthc abstract no).

Nhng lp con c nhim v implements cc abstract methods. Ta khng th khi to object ca abstract class, ch c th khai

bo bin kiu abstract class.


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Nested Classes


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Cc loi nested class

Static nested class

Inner (non-static) class: new Parent().new Inner();

Local class

Anonymous class

Type Scope Inner

static nested class member no

inner [non-static]

class member yes

local class local yes

anonymous class only the point where it is defined yes


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Kiu lit k


99/115

S lc v kiu lit k enum L tp hp c nh cc constants. Dng n gin nht:enum Days { SUNDAY, MONDAY, TUESDAY, WEDNESDAY,

THURSDAY, FRIDAY, SATURDAY };


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Li ch ca kiu lit k enum C th in ra tn c ngha. Typesafe

Namespace

S dng trong lnh switch Ta c th nh ngha thm methods, fields; implements

interface Implements Comparable, Serializable

Phng thc quan trng: values, name, ordinal, toString

Tm hiu thm: import static (Java 1.5), java.lang.Enum


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Bi 5: Giao din (Interfaces) vPackages


102/115

To v s dng interface


103/115

Interface l g?

Interface l mt tp hp cc method c khai bo nhngkhng c nh ngha

S khc nhau gia interface v abstract class: Interface khng th implement bt k phng thc no Class c th implement rt nhiu interface nhng ch c 1 super

class

Interface khng thuc mt class hierarchy Nhng lp khng c lin quan c th implements mt interface


104/115

Khai bo mt interface

Interface default l abstract.

Tt c phng thc trong interface, default (and only) l publicabstract (khng th l static)

Tt c cc bin khai bo trong interface, default (and only) lpublic static final.


105/115

Implement mt interface

Class c th implements 1 hoc nhiu interface. Cc interfaceny c khai bo sau mnh implements.

public class StockApplet extends Applet

implements StockWatcher{

}

S dng interface nh mt kiu


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S dng interfacenh mt kiutham chiu

Sau khi c nh ngha, interface c th c dng nh l mtkiu d liu (data type). Ta c th gn bin kiu interface bngmt instance ca class implements interface .

public class StockMonitor {

public void watchStock(StockWatcher watcher,

TickerSymbol tickerSymbol,

BigDecimal delta) {

...}

}


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Interface khng th m rng c

Nu ta thm phng thc mi vo interface, nhng class cimplement interface ny s b hng.

Ta ch c th nh ngha mt interface mi extends interface c,v nhng class mi s la chn dng interface mi hay

interface c.


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Static import

Ta c th import cc thnh phn static ca lp bng lnh:import static class.*; hoc import static class.memberName.

Sau trong chng trnh ta c th tham chiu n ccmember ny bng memberName.

import static java.lang.Math.*;

Ta c th truy cp n cc thnh phn static ch bng tn:PI, E, cos(), round()


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To v s dng package


110/115

Th no l mt package?

Package l mt tp hp cc kiu (classes, interfaces, enums,annotations) c lin h vi nhau cung cp kh nng bo v truycp v qun l name space.

Nhc li: nhng access modifier default (khng khai bo g) ch

c th truy cp c vi nhng i tng trong cng package.


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Cch to mt package?

Dng t kha package ; trn u cc file trongpackage.

Lnh ny nu c phi l lnh u tin trong file.package graphics;

public class Circle extends Graphic implements Draggable {

. . .

}


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Cch t tn mt package?

Tn package s tng ng vi th mc cha file sau khi dch. Vvy tn package phi ph hp vi h thng file ca h iuhnh.

Package c th cha bn trong cc package v cc file khc.VD

package com.fpt.fss.fmt;

S dng cc members ca mt


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S dng cc members ca mtpackage

Ta dng lnh import. Cc lnh import nu c phi ng ngay sau lnh package.VD

package com.fpt.fss.fmt;import java.io.*;

Lnh import java.io.* ch import cc class, interface capackage java.io m khng import cc subpackage ca packagejava.io.

Nu xy ra xung t gia cc tn trong cc package, ta phi sdng tn y : .


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Qun l file ngun v file class (1)


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Qun l file ngun v file class (2)

ng on ngu lap trinh java

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