Thread: create a test class (main method) to start(run) the class in Java

Maybe I do not understand something.
So I've created the class in Java, which does some stuff.I need to create a main method or mainClass, that will start(run) my class. (I do not mean JUnit).
Question: how to do it?
is there some sort of methodology?
described in the books somewhere?

Help me please

You should create another class that consists of the main class.

package myproject;
 
public class Helloworld {
 
public static void main(String[] args) {
            System.out.println("Hello world");
    }
}

Was that helpfull?I mean the structure is like this.I use netbeans IDE.There all i do is to right click on the project ,select new JAVA class,write the class and then creating an object of her for instance in main

Yes,I agree.but what if it is something complicated?
like this

package handler;
 
import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.ArrayList;
 
public class TextHandler extends Handler {
	private ArrayList<String> fileTypes = new ArrayList<String>();
	private String extension;
	private String data;
 
	public TextHandler(Handler next) {
		super(next);
		fileTypes.add("html");
	 	fileTypes.add("htm");
	 	fileTypes.add("css");
	 	fileTypes.add("js");
	 	}
 
	public Response handle(Request1 recvest){
 
		 String uri=recvest.getParameter("URI");
		 if (uri != null) {
		  String extension = uri.substring(uri.lastIndexOf('.')+ 1);
	     }else{
	      return super.handle(recvest);
		 }
 
		 if (!fileTypes.contains(extension)){
		  return super.handle(recvest);
		 }
		 String webRoot = Configurator.getInstance().getSettingsParameter("web-root");
	     String filePath=webRoot+uri;
 
	     File file = new File(filePath);
	     if(!file.exists()){
	      super.handle(recvest);
	     }
	     try{
           FileInputStream fis = new FileInputStream(file);
	       DataInputStream din=new DataInputStream(fis);
	       byte[] bytes;
	       int length= din.read(bytes);
	       String data=new String(bytes,0,length);
	       din.close();
	       fis.close();
	      }catch (FileNotFoundException fnfex) {
	        super.handle(recvest);
	      } catch(IOException ioex){
	        super.handle(recvest);
	      }
 
	     String[] ParamArray = {"HTTP/","Server","ContentType","Content-Length","Content-Type","Connection"};
 
	     String totalResponse = ParamArray[0]+"1.1"+"200 OK"+"/n"+
	        	    		    ParamArray[1]+"YuriyServer/2009-09-09 "+"/n"+
	        	    		    ParamArray[2]+(int)file.length()+"/n"+
	        	                ParamArray[3]+"text"+extension+"/n"+
	        	    		    ParamArray[4]+"close"+"/n";
	          ResponsBuilder responsBuilder=new ResponsBuilder();
	          responsBuilder.buildRespons(totalResponse.getBytes());
	          responsBuilder.setData(data);
 
		    }
 
 
	     }

Your answer is better.Thank you