Java

Java

1、Hello world

java 的包名需要和目录一致，类名需要与文件名一致

[sugar@Sugar java]🐳 tree .
.
└── Hello
    └── HelloWorld.java

1 directory, 1 file

HelloWorld.java

package Hello;

public class HelloWorld {

    public static void main(String[] args) {
        System.out.println("hello,world");
    }
}

[sugar@Sugar Hello]🐳 java  HelloWorld.java 
hello,world
[sugar@Sugar Hello]🐳 

2、变量定义

int y;
int x = 1;

String s = "hello";

final double PI = 3.14; // PI是一个常量
double r = 5.0;
double area = PI * r * r;

var sb = new StringBuilder();

int a, b, c;         // 声明三个int型整数：a、 b、c
int d = 3, e = 4, f = 5; // 声明三个整数并赋予初值
byte z = 22;         // 声明并初始化 z
String s = "runoob";  // 声明并初始化字符串 s
double pi = 3.14159; // 声明了双精度浮点型变量 pi
char x = 'x';        // 声明变量 x 的值是字符 'x'。

public class RunoobTest {
    // 成员变量
    private int instanceVar;
    // 静态变量
    private static int staticVar;
    
    public void method(int paramVar) {
        // 局部变量
        int localVar = 10;
        
        // 使用变量
        instanceVar = localVar;
        staticVar = paramVar;
        
        System.out.println("成员变量: " + instanceVar);
        System.out.println("静态变量: " + staticVar);
        System.out.println("参数变量: " + paramVar);
        System.out.println("局部变量: " + localVar);
    }
    
    public static void main(String[] args) {
        RunoobTest v = new RunoobTest();
        v.method(20);
    }
}

3、流程控制

出入输出

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in); // 创建Scanner对象
        System.out.print("Input your name: "); // 打印提示
        String name = scanner.nextLine(); // 读取一行输入并获取字符串
        System.out.print("Input your age: "); // 打印提示
        int age = scanner.nextInt(); // 读取一行输入并获取整数
        System.out.printf("Hi, %s, you are %d\n", name, age); // 格式化输出
    }
}

Maven

配置settings

默认读取位置

• ~/.m2

curl -O https://repo1.maven.org/maven2/archetype-catalog.xml

<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 https://maven.apache.org/xsd/settings-1.0.0.xsd">
  <localRepository>/home/sugar/.m2/repository</localRepository>
  <mirrors>
    <mirror>
      <id>alimaven</id>
      <mirrorOf>central</mirrorOf>
      <name>aliyun maven</name>
      <url>https://maven.aliyun.com/nexus/content/groups/public/</url>
    </mirror>
  </mirrors>
  <profiles>
    <profile>
      <id>archetype-catalog</id>
      <activation>
        <activeByDefault>true</activeByDefault>
      </activation>
      <properties>
        <archetypeCatalog>file:///Users/sugar/.m2/archetype-catalog.xml</archetypeCatalog>
      </properties>
    </profile>
  </profiles>
</settings>

手动下载依赖

mvn -B -f pom.xml -s /usr/share/maven/ref/settings.xml dependency:resolve

打包

mvn package

mvn demo

• https://github.com/serialt/maven-java-demo