Java Collections II

This is a collection of notes on stuff that's sort of Collections-related going beyond the first treatment.

Lists and Sets

Using a hashed set is much faster when your main activity is only to discover if a string is in a set than putting it into an array. The array has to be looked through, string by string, until a match is found. A Set's contains() method is much. Of course, you cannot install identical strings into a hashed set as you can in an array list.

List< String > list = new ArrayList< String >();

list.add( "ant" );
list.add( "cat" );
list.add( "dog" );
list.add( "aardvark" );
list.add( "dog" );           // this is okay!

if( list.contains( "dog" ) )
    ...

...versus...

Set< String > set = new HashedSet< String >();

set.add( "ant" );
set.add( "cat" );
set.add( "dog" );
set.add( "aardvark" );
//set.add( "dog" );         // can't do this!

if( set.contains( "dog" ) ) // this is much faster than with List
    ...