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บทที่2 พื้นฐานภาษา Java
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»ÃÐÇѵÔÀÒÉÒ JAVA
ÀÒÉÒ¨ÒÇÒ à»š¹ÀÒÉÒâ»Ãá¡ÃÁàªÔ§Çѵ¶Ø·Õè¾Ñ²¹Ò¢Öé¹â´Â Dr.James Gosling áÅзÕÁÇÔÈǡâͧà¢Ò «Ö觺ÃÔÉÑ· Sun Microsystems µŒÍ§¡ÒùíÒÀÒÉÒ¨ÒÇÒÁÒ㪌᷹ÀÒÉÒ C++ ¨¹ã¹»‚ ¤.È. 1995 ÀÒÉÒ¨ÒÇÒàÃÔèÁ໚¹·Õè¹ÔÂÁá¾Ã‹ËÅÒÂ
¤ÇÒÁËÁÒÂÀÒÉÒ¨ÒÇÒ (Java Language)
ÀÒÉÒ¨ÒÇÒ (Java Language) ¤×Í ÀÒÉÒ¤ÍÁ¾ÔÇàµÍÃ�·Õè¶Ù¡¾Ñ²¹Ò¢Öé¹â´ÂºÃÔÉÑ· Sun Microsystems ໚¹ÀÒÉÒÊíÒËÃѺà¢Õ¹â»Ãá¡ÃÁ·ÕèʹѺʹع¡ÒÃà¢Õ¹â»Ãá¡ÃÁàªÔ§Çѵ¶Ø (OOP : Object-Oriented Programming) â»Ãá¡ÃÁ·Õèà¢Õ¹¢Ö鹶١ÊÌҧÀÒÂ㹤ÅÒÊ Ñ§¹Ñ鹤ÅÒʤ×Í·Õèà¡çºàÁ·Í´ (Method) ËÃ×;ĵԡÃÃÁ (Behavior) «Öè§ÁÕʶҹР(State) áÅÐÃÙ»¾Ãó (Identity) »ÃШíҾĵԡÃÃÁ (Behavior)
Ø´à ‹¹¢Í§ÀÒÉÒ¨ÒÇÒ (Java Language)
1) ໚¹ÀÒÉÒÊíÒËÃѺ¡ÒÃà¢Õ¹â»Ãá¡ÃÁàªÔ§Çѵ¶Ø (OOP: Object Oriented Programming)
2) Java ¤×Í platform independence ËÁÒ¤ÇÒÁÇ‹Ò ¤ÇÒÁÊÒÁÒö¢Í§â»Ãá¡ÃÁ·Õèà¢Õ¹ ŒÇ java ÊÒÁÒö·íÒ§Ò¹ä Œã¹ Ãкº»¯ÔºÑµÔ¡Ò÷Õè µ‹Ò§¡Ñ¹ â´ÂäÁ‹µŒÍ§ Ñ´á»Å§á¡Œä¢ãËÁ‹
3) Free áÅР໚¹â»Ãá¡ÃÁ»ÃÐàÀ· Open Source
ª¹Ô´¢Í§â»Ãá¡ÃÁ Java
1) Java Application
໚¹¡ÒùíÒâ»Ãá¡ÃÁ Java ÁÒà¢Õ¹໚¹â»Ãá¡ÃÁ·ÕèÊÒÁÒö¹íÒÁÒ㪌§Ò¹ä ŒÍ‹ҧÍÔÊÃЪ¹Ô´¢Í§â»Ãá¡ÃÁ Java
2) Java Applets
໚¹¡ÒùíÒ Java ÁÒà¢Õ¹໚¹â»Ãá¡ÃÁઋ¹à ÕÂǡѹ ᵋäÁ‹ÊÒÁÒöàÃÕ¡㪌§Ò¹ä ŒµÒÁÅíҾѧ µŒÍ§¹íÒÁÒãÊ‹äÇŒã¹àÍ¡ÊÒà HTML áÅŒÇ㪌â»Ãá¡ÃÁ Web Browser ËÃ×Í Utilities ¢Í§ Java à¾×èÍàÃÕ¡ Ù¼ÅÅѾ �
â¤Ã§ÊÌҧ ÀÒÉÒ Java
µÑÇÍ‹ҧઋ¹ public class ª×èͤÅÒÊ
{ public static void main(String[] agrs) { »ÃÐ⤤íÒÊÑ觵‹Ò§æ ¢Í§â»Ãá¡ÃÁ; ..................................................; } }
â¤Ã§ÊÌҧ ÀÒÉÒ Java
à¤Ã×èͧËÁÒ 㹡ÒäǺ¤ØÁ Structure 1.1 Comment ¤×Í¢ŒÍ¤ÇÒÁ·Õèá·Ã¡à¢ŒÒä»ã¹â»Ãá¡ÃÁ ᵋäÁ‹Áռŵ‹Í¡ÒÃ
·íÒ§Ò¹ ¢Í§â»Ãá¡ÃÁ ઋ¹ã¹¡Ã³Õ·ÕàÃÒµŒÍ§¡ÒÃ͸ԺÒ Source code änj㹠â»Ãá¡ÃÁ ÇÔ¸Õ¡Òä×Í
- comment ·ÕÅÐ ºÃ÷Ѵ㪌à¤Ã×èͧËÁÒ // µÒÁ´ŒÇ¢ŒÍ¤ÇÒÁ·ÕµŒÍ§¡Òà comment
1.2 Keyword ¤×ͤíÒ·Õ¶Ù¡¡íÒ˹´änj㪌àͧáÅŒÇã¹ÀÒÉÒ Java äÁ‹ÊÒÁÒö ¹íÒÁÒ㪌㹡ÒõÑ駪×èÍÀÒÂã¹â»Ãá¡ÃÁä´Œ µÑÇÍ‹ҧઋ¹ class,boolean,char ໚¹µŒ¹
1.3 Identifiers ¤×ͪ×èÍ·Õè¼ÙŒà¢Õ¹µÑ駢Öé¹ÁÒ à¾×èÍ㪌᷹ÍÐäáçä´ŒäÁ‹Ç‹Ò¨Ð໚¹
method ,µÑÇá»Ã ËÃ×Í class ª×èÍ·Õè¶Ù¡µŒÍ§¤ÇûÃСͺ´ŒÇ µÑÇÍÑ¡Éà ,µÑÇàÅ¢ ,_,$ áÅШеŒÍ§¢Öé¹: µŒ¹´ŒÇµÑÇÍÑ¡ÉÃà·‹Ò¹Ñé¹
â¤Ã§ÊÌҧ ÀÒÉÒ Java
1.4 Separators ¤×Í ÍÑ¡ÉÃËÃ×Íà¤Ã×èͧËÁÒ·Õè㪌ẋ§á¡¤íÒã¹ÀÒÉÒ ÁÕ ´Ñ§µ‹Í仹Õé! - à¤Ã×èͧËÁÒ () 㪌ÊíÒËÃѺ 1. µ‹Í·ŒÒª×èÍ method äÇŒãËŒãÊ‹ parameter ઋ¹ private void hello( ); 2. ÃкØà§×è͹䢢ͧ if , while , for ,do ઋ¹ if ( i=0 ) 3. Ãкت×èÍ ª¹Ô´¢ŒÍÁÙÅ㹡Òà ·íÒ casting ઋ¹ String a=( String )x;
â¤Ã§ÊÌҧ ÀÒÉÒ Java
- à¤Ã×èͧËÁÒÂ{ }㪌ÊíÒËÃѺ
¡íÒ˹´¢Íºà¢µ¢Í§ method áÅÐ class
ઋ¹ class A{ }
Private void hello(){
}
2. ¡íÒ˹´¤‹ÒàÃÔÁµŒ¹ãËŒ ¡ÑºµÑÇá»Ã Array
ઋ¹ String a[]={"A","B","C"};
â¤Ã§ÊÌҧ ÀÒÉÒ Java
- à¤Ã×èͧËÁÒ [ ] 㪌ÊíÒËÃѺ
1. ¡íÒ˹´µÑÇ á»ÃẺ Array
ઋ¹ String a[ ];
2. ¡íÒ˹´¤‹Ò index ¢Í§µÑÇ á»Ã array
ઋ¹ a[ 0 ]=10;
- à¤Ã×èͧËÁÒ ; 㪌à¾×èÍ »�´»ÃÐâ¤
ઋ¹ String a ;
- à¤Ã×èͧËÁÒ , 㪌ÊíÒËÃѺ
1. ᡪ×è͵ÑÇá»Ãã¹»ÃÐâ¤
ઋ¹ String a , b , c;
- à¤Ã×èͧ ËÁÒ . 㪌ÊíÒËÃѺ
1. ᡪ×èÍ package, sub package áÅЪ×èÍclass
ઋ¹ package com.test.Test1;
2. 㪌à¾×èÍ àÃÕ¡㪌 µÑÇ á»Ã ËÃ×Í method ¢Í§ Object
ઋ¹ object.hello();
àÁ¸Í´áÊ´§¼Å·Ò§¨ÍÀÒ¾¾×é¹°Ò¹
¡ÒÃÃѺ¢ŒÍÁÙÅ·Ò§¤ÕÂ�ºÍÃ�´ã¹ÀÒÉÒ¨ÒÇҨеŒÍ§ÊÌҧÍͺà 硵�¢Í§
¤ÅÒÊ Scanner ¢Öé¹ÁÒâ´Â¨ÐµŒÍ§»ÃСÒȵÑÇá»ÃÍͺà 硵�¡‹Í¹ ઋ¹ Scanner keyboard; »ÃСÒȵÑÇá»ÃÍͺà 硵�ª×èÍ keyboard ÍÂً㹤ÅÒÊ Scanner ¨Ò¡¹Ñé¹µŒÍÊÌҧÍͺà 硵�
ÁÒâ´Â㪌¤ÕÂ�àÇÔÃ�´ new ÁÕÃٻẺ´Ñ§¹Õé µÑÇá»ÃÍͺà 硵� = new ª×èͤÅÒÊ(ÍÒÃ�¡ÔÇàÁ¹µ�); ´Ñ§¹Ñ鹶ŒÒ¨ÐãËŒµÑÇá»Ã keyboard ÃѺ¤‹Ò·Ò§á»‡¹¾ÔÁ¾�¨ÐµŒÍ§ÊÃŒÒÍͺà¨ç¡µ�¢Öé¹ÁÒâ´Â
ãËŒÁÕÍÒÃ�¡ÔÇàÁ¹µ�໚¹ System.in ´Ñ§¹Õé keyboard = new Scanner(System.in);
㹤ÅÒÊ Scanner ¹Ñé¹àÁ¸Í´ÊíÒËÃѺ͋ҹ¢ŒÍÁÙÅ»ÃÐàÀ·µ‹Ò§æËÅÒ»ÃÐàÀ· ´Ñ§¹Õé
àÁ¸Í´ÊíÒËÃѺ͋ҹ¢ŒÍÁÙÅ»ÃÐàÀ·µ‹Ò§æ
àÁ¸Í´ ¡Ò÷íÒ§Ò¹
nextByte() ÃѺ¢ŒÍÁÙÅàÅ¢¨Ò¹Ç¹àµçÁª¹Ô´ Byte ·Ò§á»‡¹¾ÔÁ¾�
nextDouble() ÃѺ¢ŒÍÁÙÅàÅ¢·È¹ÔÂÁª¹Ô´ Double ·Ò§á»‡¹¾ÔÁ¾�
nextFloat() ÃѺ¢ŒÍÁÙÅàÅ¢·È¹ÔÂÁª¹Ô´ Float ·Ò§á»‡¹¾ÔÁ¾�
nextInt() ÃѺ¢ŒÍÁÙÅàÅ¢¨Ò¹Ç¹àµçÁª¹Ô´ Int ·Ò§á»‡¹¾ÔÁ¾�
nextLine() ÃѺ¢ŒÍÁÙÅẺʵÃÔ§·Ò§á»‡¹¾ÔÁ¾�
nextLong() ÃѺ¢ŒÍÁÙŵÑÇàÅ¢ª¹Ô´ Long ·Ò§á»‡¹¾ÔÁ¾�
nextShort() ÃѺ¢ŒÍÁÙŵÑÇàÅ¢ª¹Ô´ Short ·Ò§á»‡¹¾ÔÁ¾�
àÁ¸Í´áÊ´§¼Å·Ò§¨ÍÀÒ¾¾×é¹°Ò¹
ã¹ÀÒÉÒ¨ÒÇÒ¨Ð㪌àÁ¸Í´ print áÅÐ println 㹡ÒÃáÊ´§¼Å·Ò§¨ÍÀÒ¾ â´Â¨ÐÍÂÙ‹ã¹Íͺà¨ç¡µ� out «Öè§ÍÂً㹤ÅÒÊ System ÃٻẺ¡ÒÃ㪌§Ò¹àÁ¸Í´·Ñé§Êͧ¤×Í
System.out.print(data); System.out.println(data); â´Â data ໚¹¢ŒÍÁÙÅ·Õ赌ͧ¡ÒÃáÊ´§¼Å ¡ÒÃ㪌 print ËÅѧ¨ÒáÊ´§¼Å
áŌǨÐäÁ‹¢Ö鹺Ã÷ѴãËÁ‹ ʋǹ println ¨Ð¢Ö鹺Ã÷ѴãËÁ‹ 㹡ÒÃáÊ´§¼Å´ŒÇÂàÁ¸Í´ print ËÃ×Í println ¹Ñé¹ÊÒÁÒö㪌 escape sequence ÊíÒËÃѺ¤Çº¤ØÁ¡ÒÃáÊ´§¼Åä´Œ´Ñ§µ‹Í仹Õé
Escape sequence ÊíÒËÃѺàÁ¸Í´áÊ´§¼Å·Ò§¨ÍÀÒ¾¾×é¹°Ò¹
escape sequence ª×èÍ ¤ÇÒÁËÁÒÂ
\n Newline ¢Ö鹺Ã÷ѴãËÁ‹
\t Horizontal tab á·çºá¹Ç¹Í¹
\b Backspace ¶ÍÂËÅѧ 1 ª‹Í§µÑÇÍÑ¡ÉÃ
\r Return àÅ×è͹à¤ÍÃ�à«ÍÃ�仫ŒÒÂÊØ´
\\ Backslash µÑÇÍÑ¡Éà \
\’ Single quote µÑÇÍÑ¡Éà ’
\” Double quote µÑÇÍÑ¡Éà “
ª¹Ô´¢Í§¢ŒÍÁÙÅ µÑÇá»ÃáÅФ‹Ò¤§·Õè
ª¹Ô´¢Í§¢ŒÍÁÙÅ µÑÇá»ÃáÅФ‹Ò¤§·Õè ã¹ÀÒÉÒ¨ÒÇÒẋ§¢ŒÍÁÙÅÍ͡໚¹Êͧ»ÃÐàÀ·ãËÞ‹æ ¤×Í 1. ¢ŒÍÁÙÅẺ¾×é¹°Ò¹ 2. ¢ŒÍÁÙÅẺ͌ҧÍÔ§ «Ö觨Ðᵡµ‹Ò§¡Ñ¹µÃ§¡ÒÃ͌ҧ¶Ö§µíÒá˹‹§Ë¹‹Ç¤ÇÒÁ¨íÒ «Ö觢ŒÍÁÙÅẺ͌ҧÍÔ§¨ÐÍÂÙ‹
ã¹ËÑÇ¢ŒÍ¢Í§ÊµÃÔ§ËÃ×ÍÍÒÃ�àÃÂ� ÊÒËÃѺ¢ŒÍÁÙÅẺ¾×é¹°Ò¹ ¨ÐÁÕÊÕè¡ÅØ‹Á¤×Í 1.¢ŒÍÁÙŪ¹Ô´µÃáР2.¢ŒÍÁÙŪ¹Ô´ÍÑ¡¢ÃÐ 3.¢ŒÍÁÙŪ¹Ô´¨Ò¹Ç¹àµçÁ 4.¢ŒÍÁÙŪ¹Ô´àÅ¢·È¹ÔÂÁ
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¢ŒÍÁÙÅẺµÃáÐ
ÁÕ 2 ¤‹Ò ¤×Í true(¨ÃÔ§) ¡Ñº false(à·ç¨)
¢ŒÍÁÙÅẺµÑÇÍÑ¡¢ÃÐ
µÑÇÍÑ¡¢ÃÐÁÕ¤ÇÒÁÂÒÇäÁ‹à¡Ô¹ 1 µÑÇÍÑ¡ÉèÐ㪌¤íÒÇ‹Ò char 㹡ÒÃà¡çº¢ŒÍÁÙÅŧ˹‹Ç¤ÇÒÁ ¨íÒ ŒÇÂÃËÑÊ Unicode ¡ÒáíÒ˹´¢ŒÍÁÙŵŒÍ§ÍÂÙ‹ã¹à¤Ã×èͧËÁÒ ‘ ‘ ËÃ×Í¡íÒ˹´à»š¹¤‹ÒÃËÑÊUnicode â´ÂµÃ§â´Â㪌ÊÑÞÅѡɳ� \u ¹íÒ˹ŒÒáŌǵÒÁ ŒÇÂàÅ¢°Ò¹ÊԺˡ¢Í§ÃËÑʹÑ鹡çä Œ
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ÁÕ 4 »ÃÐàÀ· ¤×Í byte, short, int áÅÐ long «Ö觵‹Ò§¡Ñ¹µÃ§¢¹Ò´Ë¹‹Ç¤ÇÒÁ¨Ò·Õè㪌à¡çº àÁ×èÍ»ÃСÒȵÑÇá»ÃáÅŒÇÊÒÁÒö¡íÒ˹´¤‹ÒãËŒµÑÇá»Ãä Œàª‹¹¡Ñ¹ ᵋ¶ŒÒµÑÇá»Ã໚¹ª¹Ô´ long ¨ÐµŒÍ§ãÊ‹ l ËÃ×Í L µÒÁËÅѧ áÅÐÂѧÊÒÁÒö¡íÒ˹´à»š¹àÅ¢°Ò¹ÊԺˡâ´Â㪌 0x ¹Ò˹ŒÒµÑÇàÅ¢ä Œ ŒÇ ¢ŒÍÁÙŪ¹Ô´àÅ¢·È¹ÔÂÁ
ÁÕ 2 ª¹Ô´ ¤×Í float ¡Ñº double â´Â float ¨Ð㪌˹‹Ç¤ÇÒÁ¨Ò 32 ºÔµ ʋǹ double ¨Ð㪌 64 ºÔµ¶ŒÒ¨Ð
¡íÒ˹´ãËŒ¢ŒÍÁÙÅ໚¹ float ¨ÐµŒÍ§ÁÕ f ËÃ×Í F µÒÁËÅѧ
ª¹Ô´¢Í§¢ŒÍÁÙÅ µÑÇá»ÃáÅФ‹Ò¤§·Õè
»ÃÐàÀ·¢ŒÍÁÙÅ ¢¹Ò´ ª‹Ç§¡ÒÃà¡çº¢ŒÍÁÙÅ boolean 1 ºÔµ à¡çº true ËÃ×Í false
char 2 亵� à¡çºÃËÑÊÍÑ¡¢ÃÐẺ Unicode
byte 1 亵� -128 ¶Ö§ +127
short 2 亵� -32,768 ¶Ö§ +32,767
int 4 亵� -2,147,483,648 ¶Ö§ +2,147,483,647
long 8 亵� -263 ¶Ö§ +263 - 1
float 4 亵� +-3.4 x 10-38 ¶Ö§ +-3.4 x 10+38
double 8 亵� +- 1.7 x 10-308 ¶Ö§ +- 1.7 x 10+308
ª¹Ô´¢Í§¢ŒÍÁÙÅ µÑÇá»ÃáÅФ‹Ò¤§·Õè
¡ÒáíÒ˹´ª×èÍáÅФÕÂ�àÇÔÃ�´ ÁÕ¡®´Ñ§¹Õé 1. ¢Öé¹µŒ¹´ŒÇ A – Z , a – z , $ ËÃ×Í _ à·‹Ò¹Ñé¹ 2. µÑǵ‹ÍÁÒ໚¹àÅ¢ËÃ×͵ÑÇÍÑ¡¢ÃеÒÁ¢ŒÍ 1 ¡çä´Œ 3. µÑǾԾÁ�ãËÞ‹áÅÐàÅç¡ÁÕ¤ÇÒÁËÁÒµ‹Ò§¡Ñ¹ 4. µŒÍ§äÁ‹ÁÕàÇŒ¹ÇÃäÃÐËÇ‹Ò§¡ÒõÑ駪×èÍ 5. µŒÍäÁ‹«éíҡѺ¤ÕÂ�àÇÔÃ�´·Õè¨ÒÇÒÃÙŒ¨Ñ¡ ¤‹Ò¤§·Õè 㪌 final »ÃСÒȤ‹Ò¤§·Õèâ´ÂÁÕÃٻẺ´Ñ§¹Õé final ª¹Ô´¢ŒÍÁÙÅ ª×èͤ‹Ò¤§·Õè = ¤‹Ò¢Í§¢ŒÍÁÙÅ;
¡Òà íÒà¹Ô¹¡Ò÷ҧ¤³ÔµÈÒʵÃ�
µÑÇ íÒà¹Ô¹¡Ò÷ҧ¤³ÔµÈÒʵÃ�
µÑÇ´íÒà¹Ô¹¡Òà ¤ÇÒÁËÁÒ µÑÇÍ‹ҧ¹Ô¾¨¹�
+ ºÇ¡ total = const + tax;
- ź cost = total – tax;
* ¤Ù³ tax = cost * rate;
/ ËÒÃ saleprice = original / 2
% ËÒÃàÍÒàÈÉ ramainder = value % 3;
¡Òà íÒà¹Ô¹¡Ò÷ҧ¤³ÔµÈÒʵÃ�
µÑÇ íÒà¹Ô¹¡Ò÷ҧ¤³ÔµÈÒʵÃ�Ẻ‹Í
ÅíÒ Ñº¤ÇÒÁÊíÒ¤Ñޢͧà¤Ã×èͧËÁÒ 1.() 2.++,-- 3.%,/,* 4.+,- 5.<,>,<=,>= 6.= =,!= 7.&& 8.ll 9.=,+=,-=,*=,/=,%=
¡Òà íÒà¹Ô¹¡Ò÷ҧ¤³ÔµÈÒʵÃ�
ã¹ÀÒÉÒ¨ÒÇÒ »ÃÐ⤠(statement) ¨Ð¨º ŒÇÂà¤Ã×èͧËÁÒ ; (semicolon) àÊÁÍ Ñ§¹Ñé¹â»Ãá¡ÃÁÊÒÁÒöà¢Õ¹ statement ä ŒÁÒ¡¡Ç‹Ò˹Öè§Ê൨àÁç¹µ�ã¹Ë¹Ö觺Ã÷Ѵ¢Í§ source code ËÃ×ÍÊÒÁÒöà¢Õ¹ statement â´ÂÁÕ¤ÇÒÁÂÒÇÁÒ¡¡Ç‹Ò˹Ö觺Ã÷Ѵ¡çÊÒÁÒö·íÒä Œ
Expression ËÁÒ¶֧ »ÃÐâ¤ã¹ÀÒÉÒ Java ·Õèä ŒÃѺ¡ÒÃÂÍÁÃѺNjÒÍÂÙ‹ã¹ÃٻẺ·Õèä Œ¡íÒ˹´äÇŒ ¡ÒÃà¢Õ¹ code ãËŒÁÕÃٻẺ·ÕèàËÁÒÐÊÁ Í‹Ò¹ä Œ§‹Ò ¨Ð·íÒãËŒ¡ÒþѲ¹Òâ»Ãá¡ÃÁ໚¹ä»ä Œ ŒÇ¤ÇÒÁÃÇ´àÃçÇáÅР໚¹·ÕèÂÍÁÃѺµÒÁÃкºÊÒ¡Å ÃٻẺ·ÕèàËÁÒÐÊÁ¹Ñ蹤×Í ¡ÒËÍ˹ŒÒ (indentation) à¾×èÍãËŒ¡ÒÃÍ‹Ò¹·íÒä Œ§‹Ò áÅÐÁͧ ÙÊǧÒÁ
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- ¡ÒÃá»Å§¢ŒÍÁÙÅãËŒÁÕ¢¹Ò´àÅç¡Å§
â´Â·ÑèÇä»ÁÑ¡¨Ðà»ÅÕè¹¢ŒÍÁÙÅãËŒÁÕ¢¹Ò´ãËÞ‹¢Öé¹ à¾ÃÒжŒÒËÒ¡á»Å§¢ŒÍÁÙÅãËŒÁÕ¢¹Ò´àÅç¡Å§ÍÒ¨·ÒãËŒ¡ÒûÃÐÁÇżŢŒÍÁÙÅà¡Ô´¤ÇÒÁàÊÕÂËÒÂä Œ
¡ÒÃá»Å§¢¹Ò´¢ŒÍÁÙÅâ´Â Cast Operator
ã¹ÀÒÉÒ¨ÒÇÒÊÒÁÒöá»Å§¢ŒÍÁÙÅ¢¹Ò´ãËÞ‹ãËŒÁÕ¢¹Ò´àÅç¡Å§ä Œâ´Â㪌 Cast Operator «Ö觨Ðà¢Õ¹»ÃÐàÀ·¢ŒÍÁÙÅ·Õ赌ͧ¡ÒÃá»Å§äÇŒã¹Ç§àÅçº ŒÒ¹Ë¹ŒÒµÑÇá»Ã·Õ赌ͧ¡Òà ઋ¹
x = (int)number;
á»Å§¢ŒÍÁÙÅã¹ number ãˌ໚¹»ÃÐàÀ· int ¡‹Í¹áÅŒÇà¡çºänj㹵ÑÇá»Ã x (x µŒÍ§à»š¹ int ŒÇÂ)
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1. ¶ŒÒµÑǶ١ íÒà¹Ô¹¡ÒõÑÇ˹Öè§à»š¹ double µÑǶ١ íÒà¹Ô¹¡ÒÃÍÕ¡µÑǨÐà»ÅÕè¹໚¹ double
2. ¶ŒÒµÑǶ١ íÒà¹Ô¹¡ÒõÑÇ˹Öè§à»š¹ float µÑǶ١ íÒà¹Ô¹¡ÒÃÍÕ¡µÑÇ·ÕèÁÕ¢¹Ò´àÅ硡NjҨж١à»ÅÕè¹໚¹ float
3. ¶ŒÒµÑǶ١ íÒà¹Ô¹¡ÒõÑÇ˹Öè§à»š¹àÅ¢¨íҹǹàµçÁ µÑǶ١ íÒà¹Ô¹¡ÒÃÍÕ¡µÑÇ໚¹ long
µÑǶ١´Òà¹Ô¹¡ÒÃÍÕ¡µÑǨж١à»ÅÕè¹໚¹ long
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¡ÒÃÊÌҧ String
String ໚¹ Class ˹Öè§ã¹ Package ¢Í§ÀÒÉÒ¨ÒÇÒª×èÍ java.lang ·íÒ
˹ŒÒ·Õèã¹ ¡ÒÃà¡çº¢ŒÍÁÙÅ·Õè໚¹ “ªØ´¢Í§µÑÇÍÑ¡ÉÔ «Ö觻¡µÔª¹Ô´¢Í§¢ŒÍÁÙŢͧÀÒÉÒ¨ÒÇÒ¡çÁÕ
ª¹Ô´à»š¹ character ᵋà¡çº¢ŒÍÁÙÅä´Œà¾Õ§ 1 µÑÇÍÑ¡ÉÃà·‹Ò¹Ñé¹ ´Ñ§¹Ñé¹ ¨Ö§ÅíҺҡ㹡ÒÃ
¹íÒÁÒ㪌¡Ñº¢ŒÍÁÙÅ·ÕèÁÒ¡¡Ç‹Ò 1 µÑÇÍÑ¡Éà ËÃ×Í·ÕàÃÕÂ¡Ç‹Ò “String” ´Ñ§¹Ñé¹ ÀÒÉÒ¨ÒÇÒ
¨Ö§ä´ŒÊÌҧ Class ÊíÒàÃç¨ÃÙ»ÁÒãËŒÊÒÁÒöàÃÕ¡㪌䴌·Ñ¹·Õ àÃÕÂ¡Ç‹Ò “String” ·Ñé§ËÁ´
¤×Í·ÕèÁҢͧ¤íÒÇ‹Ò String Class
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àÃÒÊÒÁÒöàÃÕ¡㪌àÁ¸Í´ä Œâ´ÂàÃÕ¡µÑÇá»Ã͌ҧÍÔ§¢Öé¹µÒÁ ŒÇÂà¤Ã×èͧËÁÒ¨شáÅеÒÁ ŒÇÂàÁ¸Í´ «Öè§ÁÕÃٻẺ ѧ¹Õé
µÑÇá»Ã.àÁ¸Í´(ÍÒ¡ÔÇàÁ¹µ�)
¡ÒÃ㪌 import
ã¹ÀÒÉÒ¨ÒÇÒ¤ÅÒʵ‹Ò§æ¨Ð¶Ù¡ÃÇÁänj໚¹á¾ç¡à¡¨«Öè§ÊÒÁÒöàÃÕ¡㪌 ŒÇ¤íÒÊÑè§ import
à¾×èͺ͡ãËŒ¤ÍÁä¾àÅÍÃ�ÃٌNjҨйíÒ¤ÅÒÊÁÒ¨Ò¡·Õèã´ â´Âà¢Õ¹¤íÒÊÑè§ import äÇŒ·ÕèʋǹËÑǢͧâ»Ãá¡ÃÁ ઋ¹¡ÒÃ㪌§Ò¹¤ÅÒÊ Scanner ¨ÐµŒÍ§à¢Õ¹ ѧ¹Õé
import java.util.Scanner
໚¹¡ÒÃàÃÕ¡㪌¤ÅÒÊ Scanner ·Õèà¡çºÍÂÙ‹ã¹ util â´Â util ¹Õéà¡çºÍÂÙ‹ã¹á¾ç¡à¡¨ËÅÑ¡ª×èÍ java