[FIXED] luckperms non-static method getUserManager() cannot be referenced from a static context

Issue

I'm trying to get user with uuid but an error pops up and says this:

non-static method getUserManager() cannot be referenced from a static context

I tried to place it in a different method and call that method but didn't worked, whatever I do that error still pops up. It could be because I wrote LuckPerms instead of luckPerms but I don't think so.

And here is the code (I deleted some useless stuff) I tried searching but couldn't find anything, also I've read API like 5 times and it was useless

// BUNGEECORD
import net.md_5.bungee.api.plugin.Plugin;
// BUNGEECORD

//JAVA
import java.util.EnumSet;
//JAVA

//LuckPerms
import net.luckperms.api.LuckPermsProvider;
import net.luckperms.api.LuckPerms;
//LuckPerms

        public void onPrivateMessageReceived(final PrivateMessageReceivedEvent event) {
           UUID uuid = UUID.nameUUIDFromBytes(("OfflinePlayer:" + messages.get(0).getContentDisplay()).getBytes());
           net.luckperms.api.model.user.User user = LuckPerms.getUserManager().getUser(uuid); // AND HERE IS THE ERROR
           DataMutateResult result = user.data().add(Node.builder("group.admin").build());
         };

And here is my pom.xml

<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>area</groupId>
    <artifactId>amogus</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <properties>
      <maven.compiler.source>1.8</maven.compiler.source>
      <maven.compiler.target>1.8</maven.compiler.target>
    </properties>
    <repositories>
     <repository>
         <id>dv8tion</id>
         <name>m2-dv8tion</name>
         <url>https://m2.dv8tion.net/releases</url>
     </repository>
     <repository>
         <id>spigot-repo</id>
         <url>https://hub.spigotmc.org/nexus/content/repositories/snapshots/</url>
     </repository>
     <repository>
        <snapshots>
            <enabled>false</enabled>
        </snapshots>
        <id>bintray-dv8fromtheworld-maven</id>
        <name>bintray</name>
        <url>http://dl.bintray.com/dv8fromtheworld/maven</url>
     </repository>
     <repository>
         <id>bungeecord-repo</id>
         <url>https://oss.sonatype.org/content/repositories/snapshots</url>
     </repository>
    </repositories>
    <dependencies>
        <dependency>
            <groupId>net.dv8tion</groupId>
            <artifactId>JDA</artifactId>
            <version>4.3.0_277</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>2.0.0-alpha4</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>2.0.0-alpha4</version>
        </dependency>
        <dependency>
            <groupId>net.luckperms</groupId>
            <artifactId>api</artifactId>
            <version>5.3</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
                <groupId>org.bukkit</groupId>
                <artifactId>bukkit</artifactId>
                <version>1.12.2-R0.1-SNAPSHOT</version>
                <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>net.md-5</groupId>
            <artifactId>bungeecord-api</artifactId>
            <version>1.16-R0.5-SNAPSHOT</version>
            <type>jar</type>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>net.md-5</groupId>
            <artifactId>bungeecord-api</artifactId>
            <version>1.16-R0.5-SNAPSHOT</version>
            <type>javadoc</type>
            <scope>provided</scope>
        </dependency>
</dependencies>
    <build>
    <plugins>
        <plugin>
              <groupId>org.apache.maven.plugins</groupId>
              <artifactId>maven-jar-plugin</artifactId>
              <version>3.1.0</version>
              <configuration>
                <archive>
                  <manifest>
                    <mainClass>area.amogus</mainClass>
                  </manifest>
                </archive>
              </configuration>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.5.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-shade-plugin</artifactId>
            <version>2.4.3</version>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>shade</goal>
                    </goals>
                    <configuration>
                        <artifactSet>
                            <excludes>
                                <exclude></exclude>
                            </excludes>
                        </artifactSet>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
       <resources>
     <resource>
       <directory>resources</directory>
     </resource>
   </resources>
</build>

</project>

Solution

Imagine we have a class:

public class MyClass {
    public static void main(String[] args) {
        MyClass.doThis();
    }
    
    public void doThis(){
        System.out.println("do this");
    }  
}

In this case, you will get exactly the same error as you're getting in your code. It means, we cannot access doThis() method, before an instance of MyClass is created, like

MyClass myClass = new MyClass();
myClass.doThis(); //this is valid since we have an instance to call this method on.

I would assume you have to get an instance of LuckPerms object in some way, before calling a .getUserManager() method on it. Like this:

LuckPerms luckPerms = new LuckPerms(); //assuming there's a respective constructor
luckPerms.getUserManager();

Answered By - Alex.K