JavaFX Application freeze some seconds when load many images although of loading them in background Thread

i made a class as a loader for loading images in background Thread , to add them inside the JavaFX Application ,

my problem is , although of this class works as a Task , but it cause the JavaFX Apllication freeze during images loading , and work back again normally after it finish,

The Loader Class Code :

import javafx.concurrent.Service;
import javafx.concurrent.Task;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;

public class Loader{
    private String type     = "";
    private String url      = "";
    private ImageView image = new ImageView();

    private class LoaderService extends Service{
        @Override
        protected Task createTask() {
            return new LoaderTask();
        }
    }

    private class LoaderTask extends Task{
        @Override
        protected Object call() throws Exception {
            new LoaderClass();

            return null;
        }
    }

    private String getType(){
        return this.type;
    }

    private String getUrl(){
        return this.url;
    }

    public Loader type(String type){
        this.type = type;
        return this;
    }

    public Loader url(String url){
        this.url = url;
        return this;
    }

    public ImageView getImage(){
        return this.image;
    }

    public Loader build(){
        new LoaderTask().run();
        return this;
    }

    private class LoaderClass{
        public LoaderClass(){
            switch(getType()){
                case "image":
                    this.loadImage(getUrl());
                break;
            }
        }

        private void loadImage(String url){
            try{
                getImage().setImage(new Image(url));
            }catch(Exception ex){
                System.out.println("Ex"+ex.getMessage());
            }
        }
    }
}

Example of calling the loader for images from external class to add them inside the main JavaFX Window :

StackPane Pane = new StackPane();

ImageView Icon1 = new NinjaLoader()
                                    .type("image")
                                    .url("http://localhost/images/1.png")
                                    .build()
                                    .getImage();

ImageView Icon2 = new NinjaLoader()
                                    .type("image")
                                    .url("http://localhost/images/2.png")
                                    .build()
                                    .getImage();

ImageView Icon3 = new NinjaLoader()
                                    .type("image")
                                    .url("http://localhost/images/3.png")
                                    .build()
                                    .getImage();

ImageView Icon4 = new NinjaLoader()
                                    .type("image")
                                    .url("http://localhost/images/4.png")
                                    .build()
                                    .getImage();
Pane.getChildren().addAll(Icon1,Icon2,Icon3,Icon4);

so what is the wrong in my code which cause these freezes ?

Thank you ,