How to create a (unknown) number of ArrayLists within an ArrayList?

Question

I have a problem that I'm trying to Solve. I want to create an ArrayList of unknown number of elements, and in that ArrayList place other ArrayLists. For example: A hospital queue, and within this queue I want to have different queues based in the priority of the patient.

System.out.println("whats the maximum priority?");
int maxPriority = Scan.nextInt();

//Trying to create a new ArrayList in every ArrayList index.
for(int k=0; k<maxPriority;k++){
    queues[k] = new Arraylist();
}

//trying to create a "patient"-object with a name and priority
public static patient(String name, int priority){
    this.name=name;
    this.priority=priority;
}       
// trying to get the priority of a patient//
public static getPriority(){
    return priority;
}
// Trying to add the patient last in the correct "priority queue"

public static placePatient()){
    queues.add(patient.getPriority)
}

Martin Dinov · Accepted Answer · 2014-01-12 12:14:09Z

3

For having an ArrayList within an ArrayList, just do:

ArrayList<ArrayList<Type>> list = new ArrayList<ArrayList<Type>>();

That'll give you an ArrayList of ArrayLists of type Type. You can then just add ArrayList's to list as you would add to an ArrayList normally. You don't have to know the number of elements an ArrayList will hold in advance.

answered Jan 12, 2014 at 12:14

Martin Dinov

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2 Comments

user3187178 Over a year ago

hank's for reply ! So if i type in this code. The program nows that this is an arraylist that contains Arraylists. So in this place if I write list.add(4) it ads a new list on index 4 ?? What about if I want to "find" the correct arrayList and then add a object to that arraylist ? Once again, thanks

Martin Dinov Over a year ago

Try it and see. list.add(4) will give you an error, as "4" is not an ArrayList. You can add an ArrayList with list.add(new ArrayList<Integer>()) for example. You can add to a specific index of the ArrayList with list.add(elem,index). Take a look at: docs.oracle.com/javase/7/docs/api/java/util/…, E). The API doc explains the get() method which you want as well.

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