Java基础知识第一章
Java基础01：注释
注释不会被执行，是给我们写代码的人看的，书写注释是一个非常好的习惯，平时写代码一定要注意规范
注释的种类
- 单行注释：一般在最前面加上//
public class Hello{
public static void main(String[] args){
//发出对编程世界的呐喊
System.out.print("Hello World");
}
}
- 多行注释：可以注释一段文字
public class Hello{
public static void main(String[] args){
/*
我是多行注释
我是多行注释
我是多行注释
我是多行注释
*/
System.out.print("Hello World");
}
}
- 文档注释：// JavaDoc /** */
public class Hello{
public static void main(String[] args){
/**
* @Description HelloWorld
* @Author 苏兮梦
*/
System.out.print("Hello World");
}
}
有趣的代码注释
hello kitty 可爱的小猫咪
/*
* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!` `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 $$$$$$$$$$$$$$$$$$$$$F '!h. !!!
* !!!!!!!!L '$**$$$$$$$$$$$$$$$$$$$$$$ *$$$ $$$$$$$$$$$$$$$$$$$$F !!!!!!!!!
* !!!!!!!!! d$$$$$$$$$$$$$$$$$$$$$$$$buud$$$$$$$$$$$$$$$$$$$$" !!!!!!!!!!
* !!!!!!! .<! #$$*"$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$* :!!!!!!!!!!!
* !!!!!!!!!!!!: d$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$# :!!!!!!!!!!!!!
* !!!!!!!!!!!~ : '#$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$*" !!!!!!!!!!!!!!!
* !!!!!!!!!! !!!!!: ^"**$$$$$$$$$$$$$$$$$$$$**#" .:<!!!!!!!!!!!!!!!!!
* !!!!!!!!!!!!!!!!!!!!!:... .::!!!!!!!!!!!!!!!!!!!!!!!!
* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*
*/
简易计算器
/*
* +---------------------------+
* | / |
* +---------------------------+
* | [ 1,264.45 ] |
* +---------------------------+
* | |
* | |
* | [sto] [rcl] [<--] [AC/ON] |
* | |
* | [ ( ] [ ) ] [sqr] [ / ] |
* | |
* | [ 7 ] [ 8 ] [ 9 ] [ * ] |
* | |
* | [ 4 ] [ 5 ] [ 6 ] [ - ] |
* | |
* | [ 1 ] [ 2 ] [ 3 ] [ + ] |
* | |
* | [ 0 ] [ . ] [+/-] [ = ] |
* | |
* +---------------------------+
*/
猪宝宝
// _,--. ,--._
// \ > `|>o<|' < /
// `-. .-'
// / 'e___e` \
// ( (o o) )
// _\_ `=' _/_
// / /(`-._.-')\ \
// / / `.___,' \_\
// _/ / _____ \ \_
// / _(_,--' `--._)_ \
// `' )______@______( `'
// hjw / \
// /_________________\
// \ )( /
// \ / \ /
// ) | | (
// /`-'] [`-'\
// `--' `--'
//
狗头
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* :9, . .:,..,:;;;::,.,,,,,.. .,,. ..,,,,,,.59
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* SS :: h@@@@@@@@@@#; . ... . ..,,,,iM5
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* iH8: . .. ,;iiii;,::,,,,,. .;irHA
* ,8X5; . ....... ,;iihS8Gi
* 1831, .,;irrrrrs&@
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* 9Bi,:,,,,...... ..r91;;;;;iirrsss1ss1111
*/
Java基础02：标识符和关键字
Java所有的组成部分都需要名字。类名、变量名以及方法名都被称为标识符。
标识符注意点：
- 所有的标识符都应该以字母（A-Z或者a-z），美元符（$）、或者下划线（_）开始
- 首字符之后可以是任何字符的组合
- 不能使用关键字作为变量名或方法名
- 标识符是大小写敏感的
- 合法标识符举例：age、$salary、_value、__1_value
- 非法标识符举例：123abc、-salary、#abc
- 可以使用中文命名，但是一般不建议这样去使用，也不建议使用拼音，比较Low
public static void main(String[] args){
String 王者荣耀 = "最强王者";
System.out.print("Hello World");
}
以下是Java阶段常见的关键字：
| abstract | assert | boolean | break | byte |
|---|---|---|---|---|
| case | catch | char | class | const |
| continue | default | do | double | else |
| enum | extends | final | finally | float |
| for | goto | if | implements | import |
| instanceof | int | interface | long | native |
| new | package | private | protected | public |
| return | strictfp | short | static | super |
| switch | synchronized | this | throw | throws |
| transient | try | void | volatile | while |
Java基础03：数据类型讲解
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
弱类型语言
Java的数据类型分为两大类
基本类型（primitive type）
- 整数类型
- byte占1个字节范围
- short占2个字节范围
- int占4个字节范围
- long占8个字节范围
- 浮点类型
- float占4个字节范围
- double占8个字节范围
- 字符类型
- char占2个字节范围
- boolean类型：占1位其值只有true和false两个
public class Demo{
public static void main(String[] args){
//八大基本数据类型
//整数
int num1 = 10; //最常用
byte num2 = 20;
short num3 = 30;
long num4 = 40L; //Long类型要在数字后面加个L
//小数：浮点数
float num5 = 50.1F; //float类型要在数字后面加个F
double num6 = 3.141592653589793238462643;
//字符
char name = '中';
//布尔值：是非
boolean flag = true;
//boolean flag = false;
}
}
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（byte，字节）= 8bit（位）
字符：是指计算机中使用的字母、数字、字和符号
1bit表示1位
1Byte表示一个字节 1B = 8b
1024B = 1KB
1024KB = 1M
1024M = 1G
引用类型（reference type）
- 类
- 接口
- 数组
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