Remove actor

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
import java.awt.Color;
/**
 * Write a description of class HealthBar here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class HealthBar extends ScrollingActor
{
    /**
     * Act - do whatever the HealthBar wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    int health = 100;
    int healthBarWidth = 100;
    int healthBarHeight = 30;
    int pixelsPerHealthPoint = (int) healthBarWidth/health; 

    public HealthBar(){
        act();
    }

    public int getHealth()
    {
        return health;
    }

    public void act() 
    {
        update();
        if (Greenfoot.isKeyDown("up")) {
            setRotation(270);
            move(5);
        }
        if (Greenfoot.isKeyDown("down")) {
            setRotation(90);
            move(5); 
        }
        if (Greenfoot.isKeyDown("left")) {
            setRotation(180);
            move(5); 
        }
        if (Greenfoot.isKeyDown("right")) {
            setRotation(0); 
            move(5); 
        }
    }

    public void update(){
        setImage(new GreenfootImage(healthBarWidth+2, healthBarHeight +2));
        GreenfootImage myImage = getImage();
        myImage.setColor(Color.WHITE);
        myImage.drawRect(0, 0, healthBarWidth + 1, healthBarHeight + 1);
        myImage.setColor(Color.GREEN);
        myImage.fillRect(1, 1, health * pixelsPerHealthPoint, healthBarHeight);
    }

    public void loseHealthRock(){
        health-=5;
    }

    public void loseHealthPoisonousBerries(){
        health-=7;
    }

    public void loseHealthBees(){
        health-=15;
    }

    public void addHealthBerries(){
        if(health <= 95){
            health+=5;
        }
        if(health == 96){
            health+=4;
        }
        if(health == 97){
            health+=3;
        }
        if(health == 98){
            health+=2;
        }
        if(health == 99){
            health+=1;
        }
    }

    public void addHealthFish(){
        if(health <=93){
            health+=7;
        }
        if(health == 94){
            health+=6;
        }
        if(health == 95){
            health+=5;
        }
        if(health == 96){
            health+=4;
        }
        if(health == 97){
            health+=3;
        }
        if(health == 98){
            health+=2;
        }
        if(health == 99){
            health+=1;
        }
    }
    
}

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * This class is just an example. You can delete it or change the code.
 * It's not necessary for the scrolling system.
 */
public class Bear extends ScrollingActor
{
    boolean touchingRock = false;
    boolean touchingFish = false;
    GameOver gameover = new GameOver();

    public Bear() {
        GreenfootImage image = getImage();
        image.scale(image.getWidth() *2, image.getHeight() *2);
        setImage(image);
    }

    /**
     * Here you can tell your actor what he has to do.
     */
    public void act() {
        if (getWorld() == null) return;
        if (Greenfoot.isKeyDown("up"))
        {
            setRotation(270);
            move(5);
            consume();
            checkObstacle();
        }
        if (getWorld() == null) return;
        if (Greenfoot.isKeyDown("down")) {
            setRotation(90);
            move(5); 
            consume();
            checkObstacle();
        }
        if (getWorld() == null) return;
        if (Greenfoot.isKeyDown("left")) {
            setRotation(180);
            move(5); 
            consume();
            checkObstacle();
        }
        if (getWorld() == null) return;
        if (Greenfoot.isKeyDown("right")) {
            setRotation(0); 
            move(5); 
            consume();
            checkObstacle();
        }
    }

    public void checkObstacle()
    { Actor rock = getOneIntersectingObject(Rock.class); 
        if(rock != null)
        { 
            World myWorld = getWorld();
            ExampleWorld exampleworld = (ExampleWorld)myWorld;
            HealthBar healthbar = exampleworld.getHealthBar();
            if(touchingRock == false){
                healthbar.loseHealthRock();
                touchingRock = true;
                if(healthbar.health<=0){
                    myWorld.addObject(gameover, myWorld.getWidth()/2, myWorld.getHeight()/2);
                    myWorld.removeObject(this);
                }
            }
        }
        else{
            touchingRock = false;
        }
    }

    public void consume()
    { 
        Actor berry = getOneIntersectingObject(Berry.class); 
        Actor fish = getOneIntersectingObject(Fish.class); 
        if(berry!=null)
        {     
            getWorld().removeObject(berry);
        }
        if(fish!=null)
        {     
            getWorld().removeObject(fish);
            World myWorld = getWorld();
            ExampleWorld exampleworld = (ExampleWorld)myWorld;
            HealthBar healthbar = exampleworld.getHealthBar();
            if(touchingRock == false){
                healthbar.addHealthFish();
                touchingFish = true;
            }
        }
        else{
            touchingFish = false;
        }
    }
}