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Thread: Sorting ArrayList

  1. #1
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    Default Sorting ArrayList

    Hello everyone,


    Let me describe my program a bit.


    There are 5 classes which describe Person, Tool, Building, Room and Organisation. They all have a String field so they are all similar. So I made an Abstract class which includes the getName method (which returns the name of the class)


    The problem starts in this section. I have a class which creates an ArrayList for each and every class like this:

    public class Lists implements Comparable<AllObjects> {
    	private ArrayList<Person> personList;
    	private ArrayList<Device> deviceList;
    	private ArrayList<Building> buildingList;
    	private ArrayList<Room> roomList;
    	private ArrayList<Organisation> orgList;
     
    	public Lists () {
    		this.personList = new ArrayList<Person>();
    		this.deviceList = new ArrayList<Device>();
    		this.buildingList = new ArrayList<Building>();
    		this.roomList = new ArrayList<Room>();
    		this.orgList = new ArrayList<Organisation>();
    	}

    I needed to implement comparable, because I have to sort these ArrayLists according to their Objects' names.

    But it seems that I can't write this comparison in Lists class. So I tried writing this comparable method in the ABSTRACT class of all my objects.

    But I just can't get it working. Can someone please give me a hint ?


    Here is the Person class:
    public class Person extends AllObjects {
    	private String name;
     
    	public Person (String s) {
    		this.name = s;
    	}
    	public String getName() {
        	return this.name;
        }
    }

    And the abstract class of all 5 Classes;

    public abstract class AllObjects implements Comparable<AllObjects>{
    	private String name;
     
     
    	public String getName() {
        	return this.name;
        }
     
    	public int CompareTo(Object tmp1)
        {
           tmp1 = (AllObjects) tmp1;
           int result = this.getName().compareTo(((AllObjects) tmp1).getName());
     
           return result;
        }
    }


  2. #2
    Administrator copeg's Avatar
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    Default Re: Sorting ArrayList

    Define "But I just can't get it working"...does it compile? Does it not function correctly?

  3. #3
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    Default Re: Sorting ArrayList

    Ok it was my first time sorting an ArrayList and i figured it out,

    Seems like it was a basic error.



    I was using COMPARATOR instead of COMPARABLE and i found the compareTo method overriding a bit hard to write. (Because its been just a few months since i started java..)


    But try-and-learn is the best way possible. Now I figured it all out, but thanks for your concern anyway

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