Scala 从入门到精通

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已于 2024-07-10 16:34:30 修改 · 3.9w 阅读

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#scala #开发语言 #后端 #linux #数据分析 #大数据 #云计算

于 2023-12-05 11:01:43 首次发布

Scala 从入门到精通

数据类型

scala数据类型

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>cn.lihaozhe</groupId>
  <artifactId>scala-code</artifactId>
  <version>1.0.0</version>
  <name>${project.artifactId}</name>

  <properties>
    <jdk.version>21</jdk.version>
    <!-- 公共配置 -->
    <maven.compiler.source>21</maven.compiler.source>
    <maven.compiler.target>21</maven.compiler.target>
    <maven.compiler.compilerVersion>21</maven.compiler.compilerVersion>
    <maven.compiler.encoding>utf-8</maven.compiler.encoding>
    <project.build.sourceEncoding>utf-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    <maven.test.failure.ignore>true</maven.test.failure.ignore>
    <maven.test.skip>true</maven.test.skip>

    <commons-dbutils.version>1.8.1</commons-dbutils.version>
    <commons-io.version>2.14.0</commons-io.version>
    <commons-lang3.version>3.14.0</commons-lang3.version>
    <druid.version>1.2.23</druid.version>
    <fastjson.version>2.0.51</fastjson.version>
    <fastjson2.version>2.0.51</fastjson2.version>
    <gson.version>2.11.0</gson.version>
    <hutool.version>5.8.29</hutool.version>
    <jackson.version>2.17.2</jackson.version>
    <junit.version>5.10.3</junit.version>
    <lombok.version>1.18.34</lombok.version>
    <mysql.version>8.4.0</mysql.version>
    <scala.version>2.13.14</scala.version>
  </properties>
  <dependencies>
    <dependency>
      <groupId>org.scala-tools.testing</groupId>
      <artifactId>specs_2.10</artifactId>
      <version>1.6.9</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.scalatest</groupId>
      <artifactId>scalatest_2.13</artifactId>
      <version>3.2.19</version>
      <scope>test</scope>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-api -->
    <dependency>
      <groupId>org.junit.jupiter</groupId>
      <artifactId>junit-jupiter-api</artifactId>
      <version>${junit.version}</version>
      <!-- 作用域 -->
      <scope>test</scope>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-engine -->
    <dependency>
      <groupId>org.junit.jupiter</groupId>
      <artifactId>junit-jupiter-engine</artifactId>
      <version>${junit.version}</version>
      <scope>test</scope>
    </dependency>
    <!-- https://mvnrepository.com/artifact/cn.hutool/hutool-all -->
    <dependency>
      <groupId>cn.hutool</groupId>
      <artifactId>hutool-all</artifactId>
      <version>${hutool.version}</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.apache.commons/commons-lang3 -->
    <dependency>
      <groupId>org.apache.commons</groupId>
      <artifactId>commons-lang3</artifactId>
      <version>${commons-lang3.version}</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/commons-io/commons-io -->
    <dependency>
      <groupId>commons-io</groupId>
      <artifactId>commons-io</artifactId>
      <version>${commons-io.version}</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
    <dependency>
      <groupId>com.google.code.gson</groupId>
      <artifactId>gson</artifactId>
      <version>${gson.version}</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
    <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>fastjson</artifactId>
      <version>${fastjson.version}</version>
    </dependency>
    <!--jackson-->
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-core</artifactId>
      <version>${jackson.version}</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-annotations</artifactId>
      <version>${jackson.version}</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>${jackson.version}</version>
    </dependency>
    <dependency>
      <groupId>com.fasterxml.jackson.datatype</groupId>
      <artifactId>jackson-datatype-jsr310</artifactId>
      <version>${jackson.version}</version>
    </dependency>
    <!--java 小工具-->
    <dependency>
      <groupId>com.github.binarywang</groupId>
      <artifactId>java-testdata-generator</artifactId>
      <version>1.1.2</version>
    </dependency>
    <dependency>
      <groupId>com.mysql</groupId>
      <artifactId>mysql-connector-j</artifactId>
      <version>${mysql.version}</version>
    </dependency>
  </dependencies>
  <build>
    <finalName>${project.artifactId}</finalName>
    <!--<outputDirectory>../package</outputDirectory>-->
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>3.13.0</version>
        <configuration>
          <!-- 设置编译字符编码 -->
          <encoding>UTF-8</encoding>
          <!-- 设置编译jdk版本 -->
          <source>${jdk.version}</source>
          <target>${jdk.version}</target>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-clean-plugin</artifactId>
        <version>3.4.0</version>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-resources-plugin</artifactId>
        <version>3.3.1</version>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-war-plugin</artifactId>
        <version>3.4.0</version>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>3.4.2</version>
      </plugin>
      <!-- 编译级别 -->
      <!-- 打包的时候跳过测试junit begin -->
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>3.3.0</version>
        <configuration>
          <skip>true</skip>
        </configuration>
      </plugin>
      <!-- 该插件用于将Scala代码编译成class文件 -->
      <plugin>
        <groupId>net.alchim31.maven</groupId>
        <artifactId>scala-maven-plugin</artifactId>
        <version>4.9.2</version>
        <configuration>
          <scalaCompatVersion>${scala.version}</scalaCompatVersion>
          <scalaVersion>${scala.version}</scalaVersion>
        </configuration>
        <executions>
          <execution>
            <id>scala-compile-first</id>
            <phase>process-resources</phase>
            <goals>
              <goal>compile</goal>
            </goals>
          </execution>
          <execution>
            <goals>
              <goal>testCompile</goal>
            </goals>
          </execution>
          <execution>
            <id>compile-scala</id>
            <phase>compile</phase>
            <goals>
              <goal>add-source</goal>
              <goal>compile</goal>
            </goals>
          </execution>
          <execution>
            <id>test-compile-scala</id>
            <phase>test-compile</phase>
            <goals>
              <goal>add-source</goal>
              <goal>testCompile</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-assembly-plugin</artifactId>
        <version>3.7.1</version>
        <configuration>
          <descriptorRefs>
            <descriptorRef>jar-with-dependencies</descriptorRef>
          </descriptorRefs>
        </configuration>
        <executions>
          <execution>
            <id>make-assembly</id>
            <phase>package</phase>
            <goals>
              <goal>single</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>
</project>

scala风格与java风格

public class JavaDemo01 {
   
   
  public static void main(String[] args) {
   
   
    System.out.println("我爱你中国");
  }
}

object ScalaDemo01 {
   
   
  def main(args: Array[String]): Unit = {
   
   
    println("我爱你中国")
  }
}

javac JavaDemo01

scalac ScalaDemo01

scala项目启动方式

App是scala语言内置的一个特质，使用它，则把对应object内部的整体作为scala main的一部分，有延迟启动的特性。

同时，命令行参数args也作为App特质的一部分，可以被开发者直接使用。而main函数则是scala的默认启动方式。

main函数

class ScalaDemo02 {
   
   
  def main(args: Array[String]): Unit = {
   
   
    println("我爱你中国")
  }
}

使用App特质

object ScalaDemo03 extends App {
   
   
  println("我爱你中国")
}

object ScalaDemo04 extends App {
   
   
  println(args(0))
}

scalac ScalaDemo04.scala

scala ScalaDemo04 李昊哲

变量与常量

object ScalaDemo06{
   
   
  def main(args: Array[String]): Unit = {
   
   
    // var 变量修饰符
    var a:Int = 10;
    // val 常量修饰符
    val b:Int = 10;
    a = 20;
    println(a);
    // reassignment to val
    // b = 20;
  }
}

字符串基本使用

object ScalaDemo07 {
   
   
  def main(args: Array[String]): Unit = {
   
   
    var str01:String = "我爱你"
    var str02:String = "中国"
    // java 风格
    println(str01 + str02)
    // 插值方式 与 Python 风格比较相像
    var slogan:String = "桃李不言下自成蹊"
    println(s"slogan >>> $slogan")
    println(
      """
        |我爱你中国
        |亲爱的母亲
      """.stripMargin)
  }
}

选择结构

object ScalaDemo01 {
   
   
  def main(args: Array[String]): Unit = {
   
   
    val weekDay:Int = 3
    if (weekDay == 1){
   
   
      println("星期一")
    } else if (weekDay == 2){
   
   
      println("星期二")
    } else if (weekDay == 3) {
   
   
      println("星期三")
    } else if (weekDay == 4) {
   
   
      println("星期四")
    } else if (weekDay == 5) {
   
   
      println("星期五")
    } else if (weekDay == 6) {
   
   
      println("星期六")
    } else {
   
   
      println("星期日")
    }
  }
}

分支结构

java switch

从java14开始， switch语句有了一个很大的调整，这就让swicth语句有了更多的操作和选择，在代码上，更加的简便灵活.

switch 标准方式

switch - > 用法：

switch yield 用法：

标准方式

public class ScalaDemo02 {
   
   
  public static void main(String[] args) {
   
   
    int dayOfWeek = 2;
    switch (dayOfWeek) {
   
   
      case 1:
        System.out.println("星期一");
      case 2:
        System.out.println("星期二");
      case 3:
        System.out.println("星期三");
      case 4:
        System.out.println("星期四");
      case 5:
        System.out.println("星期五");
      case 6:
        System.out.println("星期六");
      default:
        System.out.println("星期日");
    }
  }
}

輸出如下：

星期二
星期三
星期四
星期五
星期六
星期日

从输出结果发现case代码块被穿透了，使用break防止case代码执行穿透，代码如下：

public class JavaDemo02 {
   
   
  public static void main(String[] args) {
   
   
    int dayOfWeek = 2;
    switch (dayOfWeek) {
   
   
      case 1:
        System.out.println("星期一");
        break;
      case 2:
        System.out.println("星期二");
        break;
      case 3:
        System.out.println("星期三");
        break;
      case 4:
        System.out.println("星期四");
        break;
      case 5:
        System.out.println("星期五");
        break;
      case 6:
        System.out.println("星期六");
        break;
      default:
        System.out.println("星期日");
        break;
    }
  }
}

輸出如下：

星期二

switch - > 用法：

使用switch标准方式编写代码太多的break造成代码冗余可读性不高可以借助函数式接口和lambda表达式简化书写

代码如下：

int dayOfWeek = 2;
switch (dayOfWeek) {
   
   
  case 1 -> System.out.println("星期一");
  case 2 -> System.out.println("星期二");
  case 3 -> System.out.println("星期三");
  case 4 -> System.out.println("星期四");
  case 5 -> System.out.println("星期五");
  case 6 -> System.out.println("星期六");
  default -> System.out.println("星期日");
}

输出结果如下：

星期二

switch yield 用法：返回值

先来开一段标准模式的代码：

public class JavaDemo04 {
   
   
  public static void main(String[] args) {
   
   
    String weekday = null;
    int dayOfWeek = 2;
    switch (dayOfWeek) {
   
   
      case 1:
        weekday = "星期一";
        break;
      case 2:
        weekday = "星期二";
        break;
      case 3