greenfoot
Class Actor

java.lang.Object
  greenfoot.Actor

public abstract class Actor
extends java.lang.Object

An Actor is an object that exists in the Greenfoot world. Every Actor has a location in the world, and an appearance (that is: an icon).

An Actor is not normally instantiated, but instead used as a superclass to more specific objects in the world. Every object that is intended to appear in the world must extend Actor. Subclasses can then define their own appearance and behaviour.

One of the most important aspects of this class is the 'act' method. This method is called when the 'Act' or 'Run' buttons are activated in the Greenfoot interface. The method here is empty, and subclasses normally provide their own implementations.

Version:

2.2

Author:

Poul Henriksen

Constructor Summary

Actor()
Construct an Actor.

Method Summary

void	act() The act method is called by the greenfoot framework to give actors a chance to perform some action.
protected void	addedToWorld(World world) This method is called by the Greenfoot system when this actor has been inserted into the world.
GreenfootImage	getImage() Returns the image used to represent this actor.
protected java.util.List	getIntersectingObjects(java.lang.Class cls) Return all the objects that intersect this object.
protected java.util.List	getNeighbours(int distance, boolean diagonal, java.lang.Class cls) Return the neighbours to this object within a given distance.
protected java.util.List	getObjectsAtOffset(int dx, int dy, java.lang.Class cls) Return all objects that intersect the center of the given location (relative to this object's location).
protected java.util.List	getObjectsInRange(int radius, java.lang.Class cls) Return all objects within range 'radius' around this object.
protected Actor	getOneIntersectingObject(java.lang.Class cls) Return an object that intersects this object.
protected Actor	getOneObjectAtOffset(int dx, int dy, java.lang.Class cls) Return one object that is located at the specified cell (relative to this objects location).
int	getRotation() Return the current rotation of this actor.
World	getWorld() Return the world that this actor lives in.
int	getX() Return the x-coordinate of the actor's current location.
int	getY() Return the y-coordinate of the object's current location.
protected boolean	intersects(Actor other) Check whether this object intersects with another given object.
void	move(int distance) Move this actor the specified distance in the direction it is currently facing.
void	setImage(GreenfootImage image) Set the image for this actor to the specified image.
void	setImage(java.lang.String filename) Set an image for this actor from an image file.
void	setLocation(int x, int y) Assign a new location for this actor.
void	setRotation(int rotation) Set the rotation of this actor.
void	turn(int amount) Turn this actor by the specified amount (in degrees).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Actor

public Actor()

Construct an Actor. The object will have a default image.

Method Detail

act

public void act()

The act method is called by the greenfoot framework to give actors a chance to perform some action. At each action step in the environment, each object's act method is invoked, in unspecified order.

The default implementation does nothing. This method should be overridden in subclasses to implement an actor's action.

getX

public int getX()
         throws java.lang.IllegalStateException

Return the x-coordinate of the actor's current location. The value returned is the horizontal index of the actor's cell in the world.

Returns:

The x-coordinate of the object's current location.

Throws:

java.lang.IllegalStateException - If the actor has not been added into a world.

getY

public int getY()

Return the y-coordinate of the object's current location. The value returned is the vertical index of the actor's cell in the world.

Returns:

The y-coordinate of the actor's current location

Throws:

java.lang.IllegalStateException - If the actor has not been added into a world.

getRotation

public int getRotation()

Return the current rotation of this actor. Rotation is expressed as a degree value, range (0..359). Zero degrees is towards the east (right-hand side of the world), and the angle increases clockwise.

Returns:

The rotation in degrees.

See Also:

setRotation(int)

setRotation

public void setRotation(int rotation)

Set the rotation of this actor. Rotation is expressed as a degree value, range (0..359). Zero degrees is to the east (right-hand side of the world), and the angle increases clockwise.

Parameters:

rotation - The rotation in degrees.

See Also:

turn(int)

setLocation

public void setLocation(int x,
                        int y)

Assign a new location for this actor. This moves the actor to the specified location. The location is specified as the co-ordinates of a cell in the world.

If this method is overridden it is important to call this method as "super.setLocation(x,y)" from the overriding method, to avoid infinite recursion.

Parameters:

x - Location index on the x-axis

y - Location index on the y-axis

See Also:

move(int)

move

public void move(int distance)

Move this actor the specified distance in the direction it is currently facing.

The direction can be set using the setRotation(int) method.

Parameters:

distance - The distance to move (in cell-size units); a negative value will move backwards

See Also:

setLocation(int, int)

turn

public void turn(int amount)

Turn this actor by the specified amount (in degrees).

Parameters:

amount - the number of degrees to turn; positive values turn clockwise

See Also:

setRotation(int)

getWorld

public World getWorld()

Return the world that this actor lives in.

Returns:

The world.

addedToWorld

protected void addedToWorld(World world)

This method is called by the Greenfoot system when this actor has been inserted into the world. This method can be overridden to implement custom behaviour when the actor is inserted into the world.

The default implementation does nothing.

Parameters:

world - The world the object was added to.

getImage

public GreenfootImage getImage()

Returns the image used to represent this actor. This image can be modified to change the actor's appearance.

Returns:

The object's image.

setImage

public void setImage(java.lang.String filename)
              throws java.lang.IllegalArgumentException

Set an image for this actor from an image file. The file may be in jpeg, gif or png format. The file should be located in the project directory.

Parameters:

filename - The name of the image file.

Throws:

java.lang.IllegalArgumentException - If the image can not be loaded.

setImage

public void setImage(GreenfootImage image)

Set the image for this actor to the specified image.

Parameters:

image - The image.

See Also:

setImage(String)

intersects

protected boolean intersects(Actor other)

Check whether this object intersects with another given object.

Returns:

True if the object's intersect, false otherwise.

getNeighbours

protected java.util.List getNeighbours(int distance,
                                       boolean diagonal,
                                       java.lang.Class cls)

Return the neighbours to this object within a given distance. This method considers only logical location, ignoring extent of the image. Thus, it is most useful in scenarios where objects are contained in a single cell.

All cells that can be reached in the number of steps given in 'distance' from this object are considered. Steps may be only in the four main directions, or may include diagonal steps, depending on the 'diagonal' parameter. Thus, a distance/diagonal specification of (1,false) will inspect four cells, (1,true) will inspect eight cells.

Parameters:

distance - Distance (in cells) in which to look for other objects.

diagonal - If true, include diagonal steps.

cls - Class of objects to look for (passing 'null' will find all objects).

Returns:

A list of all neighbours found.

getObjectsAtOffset

protected java.util.List getObjectsAtOffset(int dx,
                                            int dy,
                                            java.lang.Class cls)

Return all objects that intersect the center of the given location (relative to this object's location).

Parameters:

dx - X-coordinate relative to this objects location.

dy - y-coordinate relative to this objects location.

cls - Class of objects to look for (passing 'null' will find all objects).

Returns:

List of objects at the given offset. The list will include this object, if the offset is zero.

getOneObjectAtOffset

protected Actor getOneObjectAtOffset(int dx,
                                     int dy,
                                     java.lang.Class cls)

Return one object that is located at the specified cell (relative to this objects location). Objects found can be restricted to a specific class (and its subclasses) by supplying the 'cls' parameter. If more than one object of the specified class resides at that location, one of them will be chosen and returned.

Parameters:

dx - X-coordinate relative to this objects location.

dy - y-coordinate relative to this objects location.

cls - Class of objects to look for (passing 'null' will find all objects).

Returns:

An object at the given location, or null if none found.

getObjectsInRange

protected java.util.List getObjectsInRange(int radius,
                                           java.lang.Class cls)

Return all objects within range 'radius' around this object. An object is within range if the distance between its centre and this object's centre is less than or equal to 'radius'.

Parameters:

radius - Radius of the circle (in cells)

cls - Class of objects to look for (passing 'null' will find all objects).

getIntersectingObjects

protected java.util.List getIntersectingObjects(java.lang.Class cls)

Return all the objects that intersect this object. This takes the graphical extent of objects into consideration.

Parameters:

cls - Class of objects to look for (passing 'null' will find all objects).

getOneIntersectingObject

protected Actor getOneIntersectingObject(java.lang.Class cls)

Return an object that intersects this object. This takes the graphical extent of objects into consideration.

Parameters:

cls - Class of objects to look for (passing 'null' will find all objects).