Auto Compile not working in Eclipse-maven- Scala Project

Question

I am working on scala project which I created in Eclipse. Whenerver I change scala file it is not reflecting it is saying "Error: Could not find or load main class com.sparkscala.MainExample" but when i build it works successfully.

pom.xml configuration :

<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/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.spark-scala</groupId>
    <artifactId>spark-scala</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>${project.artifactId}</name>
    <description>Spark in Scala</description>
    <inceptionYear>2010</inceptionYear>

    <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
        <encoding>UTF-8</encoding>
        <scala.tools.version>2.10</scala.tools.version>
        <!-- Put the Scala version of the cluster -->
        <scala.version>2.10.4</scala.version>
    </properties>

    <!-- repository to add org.apache.spark -->
    <repositories>
        <repository>
            <id>cloudera-repo-releases</id>
            <url>https://repository.cloudera.com/artifactory/repo/</url>
        </repository>
    </repositories>

    <build>
        <sourceDirectory>src/main/scala</sourceDirectory>
        <testSourceDirectory>src/test/scala</testSourceDirectory>
        <plugins>
            <plugin>
                <!-- see http://davidb.github.com/scala-maven-plugin -->
                <groupId>net.alchim31.maven</groupId>
                <artifactId>scala-maven-plugin</artifactId>
                <version>3.2.1</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>compile</goal>
                            <goal>testCompile</goal>
                        </goals>
                        <configuration>
                            <args>
                                <arg>-make:transitive</arg>
                                <arg>-dependencyfile</arg>
                                <arg>${project.build.directory}/.scala_dependencies</arg>
                            </args>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.13</version>
                <configuration>
                    <useFile>false</useFile>
                    <disableXmlReport>true</disableXmlReport>
                    <includes>
                        <include>**/*Test.*</include>
                        <include>**/*Suite.*</include>
                    </includes>
                </configuration>
            </plugin>

            <!-- "package" command plugin -->
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>2.4.1</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>
            <plugin>
                <groupId>org.scala-tools</groupId>
                <artifactId>maven-scala-plugin</artifactId>
                <executions>
                    <execution>
                        <id>scala-compile-first</id>
                        <phase>process-resources</phase>
                        <goals>
                            <goal>add-source</goal>
                            <goal>compile</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>scala-test-compile</id>
                        <phase>process-test-resources</phase>
                        <goals>
                            <goal>testCompile</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

    <dependencies>
        <!-- Scala and Spark dependencies -->
        <dependency>
            <groupId>org.scala-lang</groupId>
            <artifactId>scala-library</artifactId>
            <version>${scala.version}</version>
        </dependency>
        <dependency>
            <groupId>org.apache.spark</groupId>
            <artifactId>spark-core_2.10</artifactId>
            <version>1.2.0-cdh5.3.1</version>
        </dependency>

    </dependencies>
</project>

Answer 1

This is complex
The Scala compiler is v slow and creepy. It will run last good compiled file rather than tell you the trouble clearly. So if you are doing println("Hello World"), try changing to "Hello Something Else" to see if actually there is a compilation going on, or the IDE is just picking last good compiled file.
Plus your pom.xml is not correct. I suggest go to Eclipse's Windows -> Show View -> Problems.. you definitely have some problems. Remove them first. Clean, build and run again.
If you want to use Spark, then you have to make sure the Scala version matches the version in Eclipse project build path. Here is a good pom.xml with correct version of Spark as the only dependency. There is no need to add Scala library dependency as it is already included in Spark dependency hierarchy. Also, make sure that Scala library version in Eclipse project build path matches the one I am providing in pom.xml i.e. 2.11.x >>

<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/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.spark-scala</groupId>
    <artifactId>spark-scala</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>${project.artifactId}</name>
    <description>Spark in Scala</description>
    <inceptionYear>2010</inceptionYear>

    <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
        <encoding>UTF-8</encoding>
        <scala.tools.version>2.10</scala.tools.version>
        <!-- Put the Scala version of the cluster -->
        <scala.version>2.10.4</scala.version>
    </properties>

    <!-- repository to add org.apache.spark -->
    <repositories>
        <repository>
            <id>cloudera-repo-releases</id>
            <url>https://repository.cloudera.com/artifactory/repo/</url>
        </repository>
    </repositories>

    <build>
        <sourceDirectory>src/main/scala</sourceDirectory>
        <testSourceDirectory>src/test/scala</testSourceDirectory>
        <plugins>
            <plugin>
                <!-- see http://davidb.github.com/scala-maven-plugin -->
                <groupId>net.alchim31.maven</groupId>
                <artifactId>scala-maven-plugin</artifactId>
                <version>3.2.1</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.13</version>
                <configuration>
                    <useFile>false</useFile>
                    <disableXmlReport>true</disableXmlReport>
                    <includes>
                        <include>**/*Test.*</include>
                        <include>**/*Suite.*</include>
                    </includes>
                </configuration>
            </plugin>

            <!-- "package" command plugin -->
            <plugin>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>2.4.1</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>
            <plugin>
                <groupId>org.scala-tools</groupId>
                <artifactId>maven-scala-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

    <dependencies>
        <dependency>
            <groupId>org.apache.spark</groupId>
            <artifactId>spark-core_2.11</artifactId>
            <version>1.2.1</version>
        </dependency>
    </dependencies>
</project>