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Java基础（第一期）

xiyouiy 2021-02-06 21:23 原文

Java基础

1.注释

Java中注释有三种：

  • 单行注释 //

  • 多行注释 /* */

  • 文本注释（用的较少） /** */

书写注释是一个非常好的习惯 BAT

平时写代码一定要注意规范

//有趣的代码注释/***                                                                          
 *          .,:,,,                                        .::,,,::.          
 *        .::::,,;;,                                  .,;;:,,....:i:         
 *        :i,.::::,;i:.      ....,,:::::::::,....   .;i:,.  ......;i.        
 *        :;..:::;::::i;,,:::;:,,,,,,,,,,..,.,,:::iri:. .,:irsr:,.;i.        
 *        ;;..,::::;;;;ri,,,.                    ..,,:;s1s1ssrr;,.;r,        
 *        :;. ,::;ii;:,     . ...................     .;iirri;;;,,;i,        
 *        ,i. .;ri:.   ... ............................  .,,:;:,,,;i:        
 *        :s,.;r:... ....................................... .::;::s;        
 *        ,1r::. .............,,,.,,:,,........................,;iir;        
 *        ,s;...........     ..::.,;:,,.          ...............,;1s        
 *       :i,..,.              .,:,,::,.          .......... .......;1,       
 *      ir,....:rrssr;:,       ,,.,::.     .r5S9989398G95hr;. ....,.:s,      
 *     ;r,..,s9855513XHAG3i   .,,,,,,,.  ,S931,.,,.;s;s&BHHA8s.,..,..:r:     
 *    :r;..rGGh,  :SAG;;G@BS:.,,,,,,,,,.r83:      hHH1sXMBHHHM3..,,,,.ir.    
 *   ,si,.1GS,   sBMAAX&MBMB5,,,,,,:,,.:&8       3@HXHBMBHBBH#X,.,,,,,,rr    
 *   ;1:,,SH:   .A@&&B#&8H#BS,,,,,,,,,.,5XS,     3@MHABM&59M#As..,,,,:,is,   
 *  .rr,,,;9&1   hBHHBB&8AMGr,,,,,,,,,,,:h&&9s;   r9&BMHBHMB9:  . .,,,,;ri.  
 *  :1:....:5&XSi;r8BMBHHA9r:,......,,,,:ii19GG88899XHHH&GSr.      ...,:rs.  
 *  ;s.     .:sS8G8GG889hi.        ....,,:;:,.:irssrriii:,.        ...,,i1,  
 *  ;1,         ..,....,,isssi;,        .,,.                      ....,.i1,  
 *  ;h:               i9HHBMBBHAX9:         .                     ...,,,rs,  
 *  ,1i..            :A#MBBBBMHB##s                             ....,,,;si.  
 *  .r1,..        ,..;3BMBBBHBB#Bh.     ..                    ....,,,,,i1;   
 *   :h;..       .,..;,1XBMMMMBXs,.,, .. :: ,.               ....,,,,,,ss.   
 *    ih: ..    .;;;, ;;:s58A3i,..    ,. ,.:,,.             ...,,,,,:,s1,    
 *    .s1,....   .,;sh,  ,iSAXs;.    ,.  ,,.i85            ...,,,,,,:i1;     
 *     .rh: ...     rXG9XBBM#M#MHAX3hss13&&HHXr         .....,,,,,,,ih;      
 *      .s5: .....    i598X&&A&AAAAAA&XG851r:       ........,,,,:,,sh;       
 *      . ihr, ...  .         ..                    ........,,,,,;11:.       
 *         ,s1i. ...  ..,,,..,,,.,,.,,.,..       ........,,.,,.;s5i.         
 *          .:s1r,......................       ..............;shs,           
 *          . .:shr:.  ....                 ..............,ishs.             
 *              .,issr;,... ...........................,is1s;.               
 *                 .,is1si;:,....................,:;ir1sr;,                  
 *                    ..:isssssrrii;::::::;;iirsssssr;:..                    
 *                         .,::iiirsssssssssrri;;:.                      
 */
     
     /***                                                                    
 *            .,,       .,:;;iiiiiiiii;;:,,.     .,,                   
 *          rGB##HS,.;iirrrrriiiiiiiiiirrrrri;,s&##MAS,                
 *         r5s;:r3AH5iiiii;;;;;;;;;;;;;;;;iiirXHGSsiih1,               
 *            .;i;;s91;;;;;;::::::::::::;;;;iS5;;;ii:                  
 *          :rsriii;;r::::::::::::::::::::::;;,;;iiirsi,               
 *       .,iri;;::::;;;;;;::,,,,,,,,,,,,,..,,;;;;;;;;iiri,,.           
 *    ,9BM&,            .,:;;:,,,,,,,,,,,hXA8:            ..,,,.       
 *   ,;&@@#r:;;;;;::::,,.   ,r,,,,,,,,,,iA@@@s,,:::;;;::,,.   .;.      
 *    :ih1iii;;;;;::::;;;;;;;:,,,,,,,,,,;i55r;;;;;;;;;iiirrrr,..       
 *   .ir;;iiiiiiiiii;;;;::::::,,,,,,,:::::,,:;;;iiiiiiiiiiiiri         
 *   iriiiiiiiiiiiiiiii;;;::::::::::::::::;;;iiiiiiiiiiiiiiiir;        
 *  ,riii;;;;;;;;;;;;;:::::::::::::::::::::::;;;;;;;;;;;;;;iiir.       
 *  iri;;;::::,,,,,,,,,,:::::::::::::::::::::::::,::,,::::;;iir:       
 * .rii;;::::,,,,,,,,,,,,:::::::::::::::::,,,,,,,,,,,,,::::;;iri       
 * ,rii;;;::,,,,,,,,,,,,,:::::::::::,:::::,,,,,,,,,,,,,:::;;;iir.      
 * ,rii;;i::,,,,,,,,,,,,,:::::::::::::::::,,,,,,,,,,,,,,::i;;iir.      
 * ,rii;;r::,,,,,,,,,,,,,:,:::::,:,:::::::,,,,,,,,,,,,,::;r;;iir.      
 * .rii;;rr,:,,,,,,,,,,,,,,:::::::::::::::,,,,,,,,,,,,,:,si;;iri       
 *  ;rii;:1i,,,,,,,,,,,,,,,,,,:::::::::,,,,,,,,,,,,,,,:,ss:;iir:       
 *  .rii;;;5r,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,sh:;;iri        
 *   ;rii;:;51,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,.:hh:;;iir,        
 *    irii;::hSr,.,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,.,sSs:;;iir:         
 *     irii;;:iSSs:.,,,,,,,,,,,,,,,,,,,,,,,,,,,..:135;:;;iir:          
 *      ;rii;;:,r535r:...,,,,,,,,,,,,,,,,,,..,;sS35i,;;iirr:           
 *       :rrii;;:,;1S3Shs;:,............,:is533Ss:,;;;iiri,            
 *        .;rrii;;;:,;rhS393S55hh11hh5S3393Shr:,:;;;iirr:              
 *          .;rriii;;;::,:;is1h555555h1si;:,::;;;iirri:.               
 *            .:irrrii;;;;;:::,,,,,,,,:::;;;;iiirrr;,                  
 *               .:irrrriiiiii;;;;;;;;iiiiiirrrr;,.                    
 *                  .,:;iirrrrrrrrrrrrrrrrri;:.                        
 *                        ..,:::;;;;:::,,.                             
 */                 
/***
 *                    _ooOoo_
 *                   o8888888o
 *                   88" . "88
 *                   (| -_- |)
 *                    O\ = /O
 *                ____/`---'\____
 *              .   ' \\| |// `.
 *               / \\||| : |||// \
 *             / _||||| -:- |||||- \
 *               | | \\\ - /// | |
 *             | \_| ''\---/'' | |
 *              \ .-\__ `-` ___/-. /
 *           ___`. .' /--.--\ `. . __
 *        ."" '< `.___\_<|>_/___.' >'"".
 *       | | : `- \`.;`\ _ /`;.`/ - ` : | |
 *         \ \ `-. \_ __\ /__ _/ .-` / /
 * ======`-.____`-.___\_____/___.-`____.-'======
 *                    `=---='
 *
 * .............................................
 *          佛祖保佑             永无BUG
 */
/*
*   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!`   `4!!!!!!!!!!~4!!!!!!!!!!!!!!!!!
*   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!   <~:   ~!!!~   ..  4!!!!!!!!!!!!!!!
*   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!  ~~~~~~~  '  ud$$$$$  !!!!!!!!!!!!!!!
*   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!  ~~~~~~~~~: ?$$$$$$$$$  !!!!!!!!!!!!!!
*   !!!!!!!!!!!`     ``~!!!!!!!!!!!!!!  ~~~~~          "*$$$$$k `!!!!!!!!!!!!!
*   !!!!!!!!!!  $$$$$bu.  '~!~`     .  '~~~~      :~~~~          `4!!!!!!!!!!!
*   !!!!!!!!!  $$$$$$$$$$$c  .zW$$$$$E ~~~~      ~~~~~~~~  ~~~~~:  '!!!!!!!!!!
*   !!!!!!!!! d$$$$$$$$$$$$$$$$$$$$$$E ~~~~~    '~~~~~~~~    ~~~~~  !!!!!!!!!!
*   !!!!!!!!> 9$$$$$$$$$$$$$$$$$$$$$$$ '~~~~~~~ '~~~~~~~~     ~~~~  !!!!!!!!!!
*   !!!!!!!!> $$$$$$$$$$$$$$$$$$$$$$$$b   ~~~    '~~~~~~~     '~~~ '!!!!!!!!!!
*   !!!!!!!!> $$$$$$$$$$$$$$$$$$$$$$$$$$$cuuue$$N.   ~        ~~~  !!!!!!!!!!!
*   !!!!!!!!! **$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$Ne  ~~~~~~~~  `!!!!!!!!!!!
*   !!!!!!!!!  J$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$N  ~~~~~  zL '!!!!!!!!!!
*   !!!!!!!!  d$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$c     z$$$c `!!!!!!!!!
*   !!!!!!!> <$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$> 4!!!!!!!!
*   !!!!!!!  $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$  !!!!!!!!
*   !!!!!!! <$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$*"   ....:!!
*   !!!!!!~ 9$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$e@$N '!!!!!!!
*   !!!!!!  9$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$  !!!!!!!
*   !!!!!!  $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$""$$$$$$$$$$$~ ~~4!!!!
*   !!!!!!  9$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$    $$$$$$$Lue  :::!!!!
*   !!!!!!> 9$$$$$$$$$$$$" '$$$$$$$$$$$$$$$$$$$$$$$$$$$    $$$$$$$$$$  !!!!!!!
*   !!!!!!! '$$*$$$$$$$$E   '$$$$$$$$$$$$$$$$$$$$$$$$$$$u.@$$$$$$$$$E '!!!!!!!
*   !!!!~`   .eeW$$$$$$$$   :$$$$$$$$$$$$$***$$$$$$$$$$$$$$$$$$$$u.    `~!!!!!
*   !!> .:!h '$$$$$$$$$$$$ed$$$$$$$$$$$$Fz$$b $$$$$$$$$$$$$$$$$$$$$F '!h.  !!!
*   !!!!!!!!L '$**$$$$$$$$$$$$$$$$$$$$$$ *$$$ $$$$$$$$$$$$$$$$$$$$F  !!!!!!!!!
*   !!!!!!!!!   d$$$$$$$$$$$$$$$$$$$$$$$$buud$$$$$$$$$$$$$$$$$$$$"  !!!!!!!!!!
*   !!!!!!! .<!  #$$*"$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$*  :!!!!!!!!!!!
*   !!!!!!!!!!!!:   d$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$#  :!!!!!!!!!!!!!
*   !!!!!!!!!!!~  :  '#$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$*"    !!!!!!!!!!!!!!!
*   !!!!!!!!!!  !!!!!:   ^"**$$$$$$$$$$$$$$$$$$$$**#"     .:<!!!!!!!!!!!!!!!!!
*   !!!!!!!!!!!!!!!!!!!!!:...                      .::!!!!!!!!!!!!!!!!!!!!!!!!
*   !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*
*/

2.标识符和关键字

String Hello="dandan";//大写开头
   String ello="dandan";//小写开头
   String $ello="dandan";//美元符号开头
   String _ello="dandan";//下划线开头
开头方式仅限上面这几种
//   String 1ello="dandan";   这个就是错哒
   重要的注意事项
  // 不能用关键字作为标识符
   //标识符是大小写敏感的

3.数据类型

强类型语言：要求变量的使用要严格符合规定所有变量都必须先定义后才能使用

  • 带来的优点是安全性，缺点是慢

  • 反之就是弱类型语言（VB，JS）

八大基本数据类型

  • 整数：byte,short,int,long

  • 小数：float,double

  • 字符（一个字）：char

  • 字符串：String //String不是关键字，是类哦

  • 布尔值：boolean //判断是非用只能输出true和false

引用数据类型：接口，类，数组

什么是字节？

  • 位（bit）：是计算机 内部数据 储存的最小单位，11001100是一个八位二进制数

  • 字节（byte）：是计算机中 数据处理 的基本单位，习惯上用大写B来表示

  • 1B=8bit

  • 字符：计算机中使用的字母，字，符号，数字

电脑的32位和64位有啥区别呢？

涉及到寻址的能力，这里也贴心的提供链接寻址。

32位的内存最大只能有4GB，而64位的能扩大到128GB（理论上无限）

64位电脑能装32位的系统，32位的电脑不能装64位的系统

话说小学时候用的电脑都是64位的，这个基本不用操心哒

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