Question

I know that TreeSet stores objects in a sorted manner. But is there a way that i can customize the order?

For example if i have a treeSet:

 TreeSet t1 = new TreeSet();
    t1.add("c");
    t1.add("d");
    t1.add("a");

And now if i iterate over it>

 Iterator it1 =t1.iterator();

    while(it1.hasNext()){
      Object o1 = it1.next();
      System.out.println(o1);
    }

i will always get the order as: a>c>d, however i want it to return the order the same as i added the elements in it i.e c>d>a?

Answer 1

Since you mention about being bound to use TreeSet, something like this comes to my mind:

 Set<String> result = new TreeSet<String>(new Comparator<String>(){
    @Override
    public int compare(String arg0, String arg1) {
        return returnCode(arg0).compareTo(returnCode(arg1));
    }
 });

where:

private Integer returnCode(String p){
        int code = 0;
        String id = p.toLowerCase();
        if ("a".equalsIgnoreCase(id)) code = 3;
        else if ("b".equalsIgnoreCase(id)) code = 2;
        else if ("c".equalsIgnoreCase(id)) code = 1;
        //etc
        return new Integer(code);
 }  

So basically you are implementing your own comparator which is nothing but assigning certain integer values to the inserted String (which i assume you know already).

NOTE: this solution will not work, incase you do not catch the option in your returnCode() method. I assume you already know the data that is being fed to the TreeSet.