语法基础

1.模板与输出语句

public class Main{
    public static void main(String[] args){
        System.out.println("dcd!");     //输出字符串
    }
}

2.数据类型

public class Main{
    public static void main(String[] args){
        //变量
        byte x=1;//字节类型byte(1字节=8位)
        short ;//short类型2个字节
        int ;//int类型4个字节
        long ;//long类型8个字节
        float y=1.0f;//float类型4个字节
        double z=1d;//double类型8个字节
        boolean flag=true;//boolean类型1个字节
        char a='A';//char类型2个字节

        //常量
        final int N=10;
    }
}

3.输入

import java.util.Scanner;//小规模输出

import java.io.BufferedReader;   //大规模输出
import java.io.InputStreamReader;

public class Main{
    public static void main(String[] args) throws Exception{
    //Scanner
        //Scanner sc = new Scanner(System.in);
        //String str = sc.next(); //读取下一段字符串
        //String str = sc.nextLine();//读取下一行字符串
        //int x = sc.nextInt(), y = sc.nextInt();//读入int类型
        //nextFloat(),nextDouble();读入float、double类型

        //System.out.println(str);
        //System.out.println(x + y);

    //Buffer
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String str=br.readLine();
        System.out.println(str);
    }
}

例题1：

a*b-c*d 

https://www.acwing.com/problem/content/610/

java:

import java.util.Scanner;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        System.out.printf("DIFERENCA = %d",a*b-c*d);
    }
}

Python3

a=eval(input())
b=eval(input())
c=eval(input())
d=eval(input())

print("DIFERENCA =",a*b-c*d)

C++

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    cout<<"DIFERENCA = "<<(a*b-c*d)<<endl;
    return 0;
}

例题2

计算圆的面积 

https://www.acwing.com/problem/content/606/

import java.util.Scanner;

public class Main{
    public static void main(String[] args){
        final double PI=3.14159;
        Scanner sc = new Scanner(System.in);
        double x = sc.nextDouble();
        System.out.printf("A=%.4f",x*x*PI);
    }
}

Spring

SpringBoot makes it easy to create stand-clone, production-grade Spring based Applications that you can just run.
独立、产品级别的Spring应用

Spring组成

Spring Core
Spring AOP
Spring ORM（对象关系映射）
Spring DAO
Spring Web
Spring Context
Spring Web MVC

微服务

一个微服务架构把每一个功能元素放进一个独立的服务中，并且通过跨服务器分发这些服务进行扩展，只在需要时才复制。

每一个功能元素最终都是一个可独立替换和独立升级的软件单元。

HelloWorld

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringApplication;

/*
* @SpringBootApplication 来标注一个主程序类，说明这是一个Spring Boot应用
*/
public class HelloWorldMianApplication{
    public static void main(String[] args){
        //Spring应用启动
        SpringApplication.run(HelloWorldMianApplication.class,args);
    }
}

Controller

import org.springframework.stereotype.Controller;//对应@Controller
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class HelloController{

    @ResponseBody   //写给浏览器
    @RequestMapping("/hello")   //接收来自浏览器的hello请求
    public String Hello(){
        return "Hello World!";
    }
}

浏览器：localhost:8080/hello