Replace an element of an array inside a if java

Question

I have to create this little method inside a class that adds a planet to a galaxy, but it seems that the element k+1 in array planeta is not replaced... is it because it's inside the if statement?

public void addPlanet(String planetName, BigInt x, BigInt y, BigInt z) {        
    if (planetExists(planetName) && !complete()){       
        newSP= new SpacePoint(x,y,z);
        newPlanet= new Planet("planetName",newSP);          
        int k=this.size();      
        planeta[k+1]=planetName; //doesnt replace because its inside the if??
    }
}

I'm sorry if it's an easy question, I'm taking java classes in college and I'm really new... PS: btw thank you all, you've been my teachers for these days!! =)

planetExists checks if the planetName exists in array planeta, complete checks if the Galaxy is complete. The problems remains, can't replace the value and don't know why... (btw I have to use arrays because my teacher won't let us use ArrayList.....) — Joana Salvado
– Joana Salvado, Commented Apr 10, 2013 at 20:00

Jon Skeet · Accepted Answer · 2013-04-09 20:22:08Z

3

I suspect the problem is that you should actually be replacing planeta[k] - and incrementing size, too.

Arrays are 0-based in Java, so if your size is 2, your array might have values:

planeta[0] = "Earth";
planeta[1] = "Jupiter";

... so the next slot to fill would be planeta[2], and increment the size to 3.

A better alternative would be to use a List<String> (e.g. an ArrayList<String>) so you could just call add, and you wouldn't need to worry about overflowing the bounds of the array, etc.

answered Apr 9, 2013 at 20:22

Jon Skeet

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4 Comments

Joana Salvado Over a year ago

I've initialized the array planeta with 5000 elements (the capacity of the galaxy) with "NA". Doesn't seem to solve, but I think I will try ArrayList<String> (my teacher hasn't talked about it yet, but it's worth the shot!) thank you!

Jon Skeet Over a year ago

@JoanaSalvado: You should work out what's wrong with the current code before changing it. What makes you think that the change to the array doesn't work?

Joana Salvado Over a year ago

After I call addPlanet(...) I check if there is a planet named "planetnName" and java says that doesn't...

Joana Salvado Over a year ago

I've changed the code based in ArrayList<String> and it's the same...doesn't add the element, it only adds if it's outside the if!!

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