//------------
// Introduction to Programming Using Java: An Object-Oriented Approach
//	Arnow/Weiss
//------------
// the isPrefix method
// Chapter 10, Section 10.11, Page 427
// MODIFICATIONS:
//    the loop is wrapped in a static method, isPrefix, so
//    that it can be tested by a main method

import java.io.*;

class TestisPrefix {
	static boolean isPrefix(String s1, String s2) {
		//////////////////////////////////////////////////////////////////
		int k;	// Position k is the next one to check; the Strings match in all 
			//      positions before k.
		k  =  0;
		while  (k!=s1.length()  &&  k!=s2.length()  &&  s1.charAt(k)==s2.charAt(k))
			k++;
		boolean  s1IsAPrefix  =  k==s1.length();
		//////////////////////////////////////////////////////////////////
		return s1IsAPrefix;
	}

	static boolean testisPrefix(String s1, String s2, boolean isprefix) {
		if (isprefix != isPrefix(s1,s2)) {
			if (isprefix)
				System.err.println("Failure: says "+s1+" is NOT a prefix of "+s2);
			else
				System.err.println("Failure: says "+s1+" IS a prefix of "+s2);
			return false;
		} else
			return true;
	}

	public static void main(String[] a) throws Exception {
		boolean passes=true;
		passes &= testisPrefix("a","abc",true);
		passes &= testisPrefix("abc","abc",true);
		passes &= testisPrefix("abcd","abc",false);
		passes &= testisPrefix("a","a",true);
		passes &= testisPrefix("","a",true);
		passes &= testisPrefix("bcd","abcd",false);
		passes &= testisPrefix("bc","abcd",false);
		if (passes)
			System.out.println("isPrefix passes these tests");
		else
			System.out.println("isPrefix fails these tests");
	}
}