Actors

Each actor and object appearing in the game grid are objects extended from the class Actor. This already reflects a perfect example of object-oriented programming. Each actor has a sprite assigned through adding the picture's path to the actor's constructor. (It is also possible to add more than one picture to one actor.)

The basic idea of JGameGrid is to give each actor a dynamic "existance". As soon as the button Run in the navigation bar is clicked, a simulation cycle starts by calling the method act() periodically. The simulation periode can be change by changing the sliders position. After each cycle the background is reloaded. This makes the realization of animations easier (this concept was borrowed from Greenfoot).

Clicking the button Step the simulation cycle is executed once. This allows the user to follow the animation step by step. Clicking Reset all actors are set back to their starting positions.

Each animation can be paused by clicking on Pause and resumed with pressing the button Run or Step.

Example 1: The actor "nemo" moves horizontally from cell to cell and disappears on the right

Run this example

Edit this example in the Online-Editor

// ActorEx1.java

import ch.aplu.jgamegrid.*;
import java.awt.Color;

public class ActorEx1 extends GameGrid
{
  public ActorEx1()
  {
    super(10, 10, 60, Color.red);
    Fish nemo = new Fish();
    addActor(nemo, new Location(1, 4));
    show();
  }

  public static void main(String[] args)
  {
    new ActorEx1();
  }
}

// ------------- class Fish --------------------
class Fish extends Actor
{
  public Fish()
  {
    super("sprites/nemo.gif");
  }

  public void act()
  {
    move();
  }
}

Explaining the program code:

class Fish extends Actor	The class Fish is extended from the class Actor and inherits all non-private methods
public Fish() { super("sprites/nemo.gif"); }	Inside the constructor of the class Fish the path to the sprite is added
act()	The method act() defines what the actor is supposed to do
move()	This moves the actor to the next cell. When initializing an actor, its starting direction of 0° is set (east)
Fish nemo = new Fish()	This initializes an object nemo of the class Fish. Since Fish extended the class Actor, nemo is an actor
addActor(nemo, new Location (1 , 4))	The actor is added to the game grid at the given location. In a grid of 10x10 cells the coordinates x and y can have a value of 0 to 9. The sprite of the actor is centered to the cell and can overlap the cell's border
show()	The game window and all its actors are shown

Alternative: Nemo as an instance of the class Actor

If you do not want to strictly follow the object-oriented design of java programming, the object nemo can be initialized as an instance of the class Actor inside the main class. Since the method act() is called automatically by the class GameGrid, the actions of the actors can be defined inside the main class as well. This alternative allows the user to drop the class Fish and makes the program code easier.

// ActorEx2.java

import ch.aplu.jgamegrid.*;
import java.awt.Color;

public class ActorEx2 extends GameGrid
{
  private Actor nemo = new Actor("sprites/nemo.gif");

  public ActorEx2()
  {
    super(10, 10, 60, Color.red);
    addActor(nemo, new Location(1, 4));
    show();
  }

  public void act()
  {
    nemo.move();
  }

  public static void main(String[] args)
  {
    new ActorEx2();
  }
}

Explaining the program code:

private Actor nemo = new Actor("sprites/nemo.gif")	This initializes the instance nemo of the class Actor. The path of the sprite needs to be set. Since nemo is used inside the method act() it must be declared as an instance variable
nemo.move()	Since move() is a method of the class Actor, nemo must be written in front of it

GameGrid: Game programming with Java	Deutsch
Research project PHBern

GameGrid: Game programming with Java

Actors

Alternative: Nemo as an instance of the class Actor