Creating new objects from array to array

Question

I'm trying to generate new unique objects from an array of all possible objects to another array. The idea is that I have 3 classes that implement Region class and they have their own methods. These 3 classes are in my ArrayList<Region> arr. I pick a random class and add it to ArrayList<Region> ALL_REGIONS in a for loop. The problem is that the object that is added from arr is not unique, they are the same. This ca be told by their name. Every Region must have it's unique name and other settings but they don't. So this is the code I have so far:

public void generateRegions(){
    ArrayList<Region> arr = Regions.getAllRegions();
    Random rnd = new Random();
    String ntype;
    int regcounter = 5;
    int b;

    for(int i = 0; i < regcounter; i++){
        ALL_REGIONS.add(arr.get(rnd.nextInt(arr.size())));
        ntype = "n" + ALL_REGIONS.get(i).getType();

        b = rnd.nextInt(Regions.getNtypeSize(ntype));
        UI.print("b: " + b);
        ALL_REGIONS.get(i).setName(Regions.getArrayName(ntype, b));
    }
}

public static ArrayList<Region> getAllRegions(){
    ArrayList<Region> arr = new ArrayList<Region>();

    arr.add(new Highlands());
    arr.add(new Cave());
    arr.add(new Oasis());

    return arr;
}

getArrayName returns a String name of the Region from an array and getNtypeSize returns an int, size of the array String[] that contatins all names which is not really important just now.

So.. how can I have every Cave, every Oasis unique/as a separate object?

**EDIT: ** Requested getArrayName() and getNtypeSize() methods are below:

public static String getArrayName(String ntype, int t) {
    String ans = null;

    if(ntype.equals("ncave")){
        if(t<=ncaveSize)
            ans = ncave[t];
    }else if(ntype.equals("noasis")){
        if(t<=noasisSize)
            ans = noasis[t];
    }else if(ntype.equals("nhighlands")){
        if(t<=noasisSize)
            ans = nhighlands[t];
    }

    //Can happen when t is bigger then ntype size or
    // if ntype string is wrong
    if(ans == null){
        UI.printerr("getArrayNames: ans is empty/null");
    }
    UI.printerr(ans);
    return ans;
}

public static int getNtypeSize(String ntype){
    int ans = 0;

    if(ntype.equals("ncave")){
            ans = ncaveSize;
    }else if(ntype.equals("noasis")){
            ans = noasisSize;
    }else if(ntype.equals("nhighlands")){
            ans = nhighlandsSize;
    }else
        UI.printerr("getNtypeSize: returned 0 as an error");

    return ans;
}

So you need to get back each element in the array as object of its initial type, right? — Ahmed Hamdy
– Ahmed Hamdy, Commented May 28, 2014 at 19:16

jithinpt · Accepted Answer · 2014-05-28 19:53:00Z

1

The issue is in this line:

ALL_REGIONS.add(arr.get(rnd.nextInt(arr.size())));

Here, you're not adding a new object to ALL_REGIONS. Rather, each time you're adding a reference to an object in 'arr'.

For example, each time rnd.nextInt(arr.size()) returns 2, you would add a reference to arr[2] to ALL_REGIONS. Thus, effectively, each entry in ALL_REGIONS refers to one of the objects in arr. (In this specific example, one of 3 objects you added in getAllRegions())

Effectively, this means that every Highlands object reference in ALL_REGIONS points to the same object => arr[0] Similarly, every Cave reference in ALL_REGIONS points to arr[1] and every Oasis reference points to arr[2]

Something along this line should fix the issue:

Region reg = arr.get(rnd.nextInt(arr.size()))  
ALL_REGIONS.add(reg.clone()); // this is just meant to be a sort of pseudo-code. Use a clone() method to create a new copy of the object and that copy to ALL_REGIONS.

edited May 28, 2014 at 19:53

answered May 28, 2014 at 19:18

jithinpt

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8 Comments

Vitalij Kornijenko Over a year ago

I looked at those and found them doing their work correctly but I will post an EDIT: shortly

user1803551 Over a year ago

@VitalijKornijenko While at it, make your code a minimal example that we can run, and add what output you get and what you expect.

Kick Buttowski Over a year ago

@jihinpt you can put your comment in comment area cuz it is not an answer. you should delete it in order avoiding to get voted down.

jithinpt Over a year ago

@Kick: Sure. I'll edit it. Its just that it doesnt allow me to add comments since my points is less than 50. Sorry about that.

Kick Buttowski Over a year ago

@jithinpt your formatting is too bad. just fix it up cuz you gonna get voted down too

|

Ahmed Hamdy · Accepted Answer · 2014-05-28 19:19:24Z

1

If I got it right? You want to cast back to the type of the original object. It is plenty easy to do so, you will use some of the Java Polymorphism concepts. You will use a function called InstanceOf like this

Region ob = arr[0];
if (ob instanceof Highlands)
    Highlands newOb = (Highlands) ob;

answered May 28, 2014 at 19:19

Ahmed Hamdy

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