Greenfoot

Penlos

2017/5/25

#

Hi, I am currently programming a game, in which you shoot birds, who are spawning random on the screen and move around. But I want to limit the number of birds flying around to 15 at the same time. My problem is: Where should I put the code for it? The birds are spawned from the world and I already tried limiting their number in constructor and act in the bird actor class with getWorld().numberOfObjects()>15 , but in the constructor it doesn't work and in act they would stop their moving. I just want the program to stop spawning them, until there are less than 15 birds. Thanks in forward.

Trystar360

2017/5/25

#

i would do something like this in the world

    public int numOfBirds = 15;
    public void act()
    {
        if(numOfBirds > 0)
        {
            //your code to spawn the birds
            numOfBirds --;
        }
    }

then in the bird class

public void die()
    {
        MyWorld world = (MyWorld)getWorld();
        world.numOfBirds ++;
        world.removeObject(this);
    }

Super_Hippo

2017/5/25

#

You should be able to limit it in the world's act method. But you should check for <15 and not >15 (in case that wasn't a typo).

Penlos

2017/5/25

#

Super_Hippo wrote...

You should be able to limit it in the world's act method.

My program spawns birds all the time, so how could I limit it in world's act method? In the worlds act method I can't access the number of birds in the world. Trystars360's code would be possible, but it doesn't work with my programming that well, so I would prefer it, if I just could check anywhere how many birds are flying around at the moment and then let the program stop spawning birds until there are less than 15 birds.

Trystar360

2017/5/25

#

in the world prepare you could do

for(int b = 15; b > 0; b --)
{
       // add bird
}

Trystar360

2017/5/25

#

but if you do the other one right it will keep track of how many birds are in the world. as long as whenever you remove a bird you add one to numOfBirds.

Super_Hippo

2017/5/25

#

Why can't you get the number of birds in your world's act method?

public void act()
{
    if (getObjects(Bird.class).size()<15 && Greenfoot.getRandomNumber(50)==0)
    {
        addObject(new Bird(), Greenfoot.getRandomNumber(getWidth()), Greenfoot.getRandomNumber(getHeight()));
    }
}

Penlos

2017/5/25

#

Trystar360 wrote...

but if you do the other one right it will keep track of how many birds are in the world. as long as whenever you remove a bird you add one to numOfBirds.

You are right, it's a good idea, but it would be a little bit boring, if always when you kill a bird immediately another spawns.

Penlos

2017/5/25

#

Super_Hippo wrote...

Why can't you get the number of birds in your world's act method?

public void act()
{
    if (getObjects(Bird.class).size()<15 && Greenfoot.getRandomNumber(50)==0)
    {
        addObject(new Bird(), Greenfoot.getRandomNumber(getWidth()), Greenfoot.getRandomNumber(getHeight()));
    }
}

That is a good idea, but why do you use Greenfoot.getRandomNumber(50)==0)?

Super_Hippo

2017/5/25

#

This way the next one won't immediately spawn.

Penlos

2017/5/25

#

Super_Hippo wrote...

This way the next one won't immediately spawn.

Ah, I see. Great idea. Works well, but now, if I do nothing and kill no birds I get a problem: java.lang.NullPointerException at Bird.act(Bird.java:41) at greenfoot.core.Simulation.actActor(Simulation.java:604) at greenfoot.core.Simulation.runOneLoop(Simulation.java:562) at greenfoot.core.Simulation.runContent(Simulation.java:221) at greenfoot.core.Simulation.run(Simulation.java:211)

danpost

2017/5/25

#

Penlos wrote...

now, if I do nothing and kill no birds I get a problem: java.lang.NullPointerException at Bird.act(Bird.java:41)

Need to see the Bird class codes. Indicate which line is line 41.

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How to limit spawning?