class Solutions {
	public static void main(String[] args){
		String s = "Hello";
		String s1;
		s1 = s.substring(0,0);
		System.out.println("="+s1);

		s1 = s.substring(0,1);
		System.out.println("="+s1);

		s1 = s.substring(2,2);
		System.out.println("="+s1);

		s1 = s.substring(4,5);
		System.out.println("="+s1);

		//System.out.println( s.startsWith(null) );
		System.out.println( s.startsWith("") );
		System.out.println( s.startsWith("e") );
		System.out.println( s.startsWith("H") );
		System.out.println( s.startsWith("Hello") );
		System.out.println( s.startsWith("Hello World") );

		System.out.println("---");

		//System.out.println( startsWith(s,null) );
		System.out.println( startsWith(s,"") );
		System.out.println( startsWith(s,"e") );
		System.out.println( startsWith(s,"H") );
		System.out.println( startsWith(s,"Hello") );
		System.out.println( startsWith(s,"Hello World") );

		printWords("You #!@ Miserable earthworms! Numbskulls! and Carpet-sellers!");

		WordIterator wi = new WordIterator("You #!@ Miserable earthworms! Numbskulls! and Carpet-sellers!");
		while (wi.hasMore())
			System.out.println(wi.next());
	}

	public static boolean startsWith(String s, String prefix) {
		if(prefix == null) throw new NullPointerException();
		if (prefix.length()>s.length()) return false;
		for(int i = 0; i<prefix.length();i++)
			if (s.charAt(i) != prefix.charAt(i) )
				return false;
		return true;
	}

	/* pre: s != null
	 * post: the words in s has been printed
	 */
	public static void printWords(String s){
		int index =0;
		int N = s.length();
		while (index<N){
			// move index to next letter
			while ( (index<N) && !Character.isLetter( s.charAt(index) ) ) index++;
			// index points to a letter
			while ( (index<N) && Character.isLetter( s.charAt(index) ) ){
				System.out.print(s.charAt(index));
				index++;
			}
			System.out.println();
		}
	}

}

class WordIterator {
	// classinv: all characters less than index has been processed and
	// 			 word is empty if and only if there are no more words.
	//			 N is the length of the string s.
	private String s;
	private int index;
	private final int N;
	private String word;
	public WordIterator(String s){
		this.s = s;
		N = s.length();
		index=0;
		moveToLetter();
		getWord();
	}
	private void moveToLetter(){
		while ( (index<N) && !Character.isLetter( s.charAt(index) ) ) index++;
	}

	private void getWord(){
		word = "";
		while ( (index<N) && Character.isLetter( s.charAt(index) ) ){
			word += s.charAt( index );
			index++;
		}
	}
	public boolean hasMore(){
		return word.length() > 0;
	}

	public String peek(){
		return word;
	}

	public String next(){
		String result = peek();
		moveToLetter();
		getWord();
		return result;
	}
}