Health

public class YourWorldName extends World
{
    public Bar hpBar;

    public YourWorldName()
    {
        super(worldWidth, worldHeight, 1);
        //Replace the parameters with what you want.
        hpBar = new Bar("Player:", "HP", startingHealth, maximumHealth));
        addObject(hpBar, xPosition, yPosition);
        
        //The rest of your constructor
    }
    
    //The rest of the class
}

public YourActor extends Actor
{
	Class[] damagingClasses = {
		Enemy.class,
		Fire.class,
		Spike.class
	};
	
	public void act()
	{
		checkForDamage();
		checkForHealing();
		
		//The rest of your act() method
	}

	private void checkForDamage()
	{
		int damageAmount = 40; //Change this to whatever
		for(Class clss : damagingClasses)
			if(isTouching(clss))
				((YourWorldName)getWorld()).hpBar.subtract(damageAmount);
	}
	
	private void checkForHealing()
	{
		//I've left this method not done
		//so you can try to do it - I find
		//the best way to learn is through
		//attempting it yourself.
	}

	private boolean isTouching(Class clss)
	{
		return getOneIntersectingObject(clss) != null;
	}
}