Why is the interface inside the class and the constructor of the class takes a parameter of the same interface

Question

Why does MyCanvas(VisualizerProvider listener) have a parameter of type VisualizerProvider listener while the interface is defined below, and the class has not been initialized yet?

import java.awt.Canvas;
import java.awt.Graphics;

/**
 *
 * @author ACER
 */
public class MyCanvas extends Canvas{
    public static final long serialVersionUID = 2L;
    
    private VisualizerProvider listener;
    
    public MyCanvas(VisualizerProvider listener){
        super();
        this.listener = listener;
    }
    
    @Override
    public void paint(Graphics g){
        super.paint(g);
        clear(g);
        listener.onDrawArray();
    }
    
    public void clear(Graphics g){
        g.setColor(ColorManager.CANVAS_BACKGROUND);
        g.fillRect(0,0, getWidth(), getHeight());
    }
    
    public interface VisualizerProvider{
        void onDrawArray();
    }
}