如何在一组Java对象中共享一个名称？

Question

The title may or may not make sense, but my question is how can I "override" an object to a different type?

I doubt this is even possible, but I'm not quite sure how to tackle this problem any other way.

I am creating a small platforming game in Java, and all the levels are assigned to class objects. Such as Level 1 would be in the class Level1, and instantiated by:

Level1 platforms = new Level1();

The way I draw objects (and similarly check for collision) is described in this loop:

Level1 platforms = new Level1();
//grabs number of platforms for level 1
int platformNum = platforms.getNumberOfPlatforms();
//creates platforms for level 1
for(int i=0;i<=platformNum;i++){
    int x1=platforms.getPlatformCoords(i,1);
    int y1=platforms.getPlatformCoords(i,2);
    int x2=platforms.getPlatformCoords(i,3);
    int y2=platforms.getPlatformCoords(i,4);
    x2-=x1;
    y2-=y1;
    g.fillRect(x1,y1,x2,y2);
}

How can I change the statement Level1 platforms = new Level1(); so that platforms can be of a certain type depending on a variable level , such that when level == 1 , platforms will be of Level1 , and so forth?

Answer 1

Just use a FactoryMethod:

Level platform = LevelFactory.getLevel(level);

Inside LevelFactory:

public Level getLevel(int level){
   if(level==1)return new Level1();
   if(level==2)return new Level2();
 //...
}

In order for this to work, each level has to extend or implement a Level class or interface.

Answer 2

There's a bit of a code smell to this, but what I think you want is an interface for a basic Level . To add to that, you're going to want to use a factory to create the levels for you on the fly.

public class LevelFactory {

    public Level getLevel(int level) {
        switch(level) {
            case 1:
            return new Level1();
            case 2:
            return new Level2();
            default:
            throw new IllegalArgumentException("Level not valid");
        }
    }
}

public interface Level {
    int getNumberOfPlatforms();
    int getPlatformCoords(int x, int y);
}

In that instance, so long as all of your levels implement Level ...

public class Level1 implements Level { }

public class Level2 implements Level { }

...you would just need to get the level you care about at the time to use.

Level platforms = LevelFactory.getLevel(1);