Searching for a record in a TreeSet on the fly

Question

I\'m writing a contact book application in Java using the swing and awt libraries. The Application consists of a JList which uses a TreeSet as an abstractListModel.

Answer 1

If you want to find all entries that start with the text (e.g. "f"), you can use the subSet(from, to) method, like this:

SortedSet<String> s = new TreeSet<String>(new Comparator<String>() {
  public int compare( String s1, String s2 ) {
    return s1.compareToIgnoreCase( s2 );
  }

});


s.add( "Erich" );
s.add( "Erica" );
s.add( "Erin" );
s.add( "Dave" );
s.add( "Thomas" );

SortedSet<String> result = s.subSet( "e", "e" + Character.MAX_VALUE ); //"e" represents the user input
System.out.println(result);//prints [Erica, Erich, Erin]

result = s.subSet( "Eric", "Eric" + Character.MAX_VALUE );
System.out.println(result); //prints [Erica, Erich]

result = s.subSet( "Erich", "Erich" + Character.MAX_VALUE );
System.out.println(result); //prints [Erich]

Since the toparameter to subset(from, to) is exclusive, you need something that will clearly be greater. In my example I simply added Character.MAX_VALUE but you might want to get some better upper bound. Note that this depends on your comparator, e.g. how it handles case differences etc.

If you want to filter using wildcards, like all texts containing the text (e.g. f would translate to *f*), you'd have to iterate over and check all the entries anyways. In that case you don't get any advantage using a sorted set.

Edit: updated the example to your data (adding me as well :) ).

Answer 2

You can use boolean startsWith(String prefix) method of java.lang.String class to check if which values in the set starts with the input string.

Ex :

public void getName(Set<String> t, String s)
    {
        for(String str : t) 
        {
            if(str.toLowerCase().startsWith(s.toLowerCase()))
                System.out.println(str);
        }
    }

input :

Set<String> test = new TreeSet<String>();

        test.add( "Erich" );
        test.add( "Erica" );
        test.add( "Erin" );
        test.add( "Dave" );
        test.add( "Thomas" );

if you call the method :

getName(test, "eri");

output will be :

Erica
Erich
Erin