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# 基础语法
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### 注释
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##### 单行
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//······//
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##### 多行
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/* ······· */
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##### 文档注释（JAVA特有）
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文档注释可以被 javadoc 解析，生成一套以网页文件形式体现该程序的说明文档
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/** ········ */
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API文档：
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### 标准输出输入
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```java
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calss PersonalInfo{
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public static void main(String[] args){
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System.out.println("~~~");
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}
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}
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```
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### 变量
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##### 数据类型
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数据类型 标识符 = 数值 ;
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###### 整型
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byte 1字节
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short 2字节
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int 4字节
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long 8字节
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###### 浮点型
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float 单精度 4字节
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double 双精度 8字节
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###### 字符类型和布尔类型
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char 2字节
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boolean a = true ;
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boolean b = false ;
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4字节
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##### 变量的自动类型提升和强制转换
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容量小与容量大的变量做运算时，结果自动转换为容量大的数据类型（容量不☞内存，☞范围）
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反之报错 （反之容易泄露）
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### String类
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字符串
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String str = "";
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运算：双引号连接，单引号加法
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### 运算符
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| 算数运算符 | 赋值运算符 | 比较运算符 |
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| :-------------: | :----------------------------------------: | :-------------: |
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| +,-,*,/,%,++,-- | =,+=,-=,*=,/=,%=,>>=,<<=,>>>=,&=,\|=,^= 等 | <,<=,>,>=,==,!= |
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| 逻辑运算符 | 位运算符 | 条件运算符 | Lambda运算符 |
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| :--------------: | :----------------: | :--------------: | :----------: |
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| &,\|,^,!,&&,\|\| | &,\|,^,~,<<,>>,>>> | 条件?结果1:结果2 | -> |
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### 标准输入输出流
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```java
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//导包
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import java.util.Scanner;
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class Scannertest{
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public static void main(String[] args){
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System.out.println("输出");
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//定义
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Scanner scan = new Scanner(System.in);
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//使用
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String name = scan.next();
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}
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}
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```
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##### 生成随机数
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在指定范围内生成随机数
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Math类中的random方法，返回一个[0.0,1.0)之间的数
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### 数组
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##### 一维数组
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###### 初始化
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```java
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//声明
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double[] prices;
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//赋值
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prices = new double[]{20.32,4.1,5.1}
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```
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```java
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String [] foods = new String[4];
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```
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##### 二维数组
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###### 初始化
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```
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String [] foods = new String[4][4];
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```
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##### 数组常用方法
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```java
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import java.util.Arrays;
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public class Main {
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public static void main(String[] args) {
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int[] arr1 = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
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int[] arr2 = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
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//比较
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System.out.println(Arrays.equals(arr1,arr2));
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//输出
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System.out.println(Arrays.toString(arr1));//包含括号
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//填充
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Arrays.fill(arr1, 0);
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System.out.println(Arrays.toString(arr1));
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//排序
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int[] arr3 = {1, 123, 3, 123, 5, 2323, 7, 8, 9, 0};
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Arrays.sort(arr3);
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System.out.println(Arrays.toString(arr3));
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//二分查找，前提必须有序
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int index = Arrays.binarySearch(arr3, 2323);
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//返回下标，找不到返回负数
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}
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}
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```
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