import java.util.ArrayList;

interface Condition
{
    public abstract boolean satisfiesCondition( String s );
}

class WordsLen implements Condition
{
    public WordsLen( int theLen )
    {
        len = theLen;
    }
    
    public boolean satisfiesCondition( String s )
    {
        return s.length( ) == len;
    }
    
    private int len;
}



class WordsTwiceInRow implements Condition
{
    public boolean satisfiesCondition( String s )
    {
        for( int i = 1; i < s.length( ); i++ )
            if( s.charAt( i ) == s.charAt( i - 1 ) )
                return true;
        
        return false;
    }
}

class WordsStartWithVowel implements Condition
{
    public boolean satisfiesCondition( String s )
    {
        char t = s.charAt( 0 );

        if( t == 'a' || t == 'e' || t == 'i' || t == 'o' || t == 'u' )
            return true;

        
        return false;
    }
}

class Day15
{
    public static ArrayList<String> countWords( String [ ] arr, Condition f )
    {
        ArrayList<String> result = new ArrayList<String>( );
        
        for( String s : arr )
            if( f.satisfiesCondition( s ) == true )
                result.add( s );
        
        return result;
    }
    
    
    public static void main( String [ ] args )
    {
        String [ ] arr = { "hello", "world", "this", "if", "that", "too" };
        
        // Count number of words of length 5
        System.out.println( countWords( arr, new WordsLen( 5 ) ) );
        
        // Count number of words of length 4
        System.out.println( countWords( arr, new WordsLen( 4 ) ) );
        
        // Count number of words contains the same letter twice in a row
        System.out.println( countWords( arr, new WordsTwiceInRow( ) ) );
        
        // Count number of words starting with a vowel
        System.out.println( countWords( arr, new WordsStartWithVowel( ) ) );
        
    }
}