package co.spillikin.java.jkia;

import java.util.ArrayList;

/**
 * Java Know It All:   String concatenation.
 * 
 * Know it all #1:  You must concatenate StringBuffer, not String in order to
 * achieve best performance.  Convert to String when finished.
 * Know it all #2:  No you don't.  The JIT optimizes concatenation for you.
 * 
 * Let's find out!!
 * 
 * @author chris
 *
 */
public class StringKIA {

	// Number of times to rerun each concatenation
	private		static		long		AWHOLELOTOFTIMES =  512;
	// Length of each String / StringBuffer
	private		static		long		SIZE = 256;
	// Useless work so JIT doesn't say "Hey, String isn't used for anything!"
	private		ArrayList<String>		useless = new ArrayList<String>();
	
	public static void main(String[] args) {

		StringKIA me = new StringKIA();
		
		System.out.println("All strings are " + SIZE + " in length and " +
				"assembled one character at a time.");
		
		System.out.println("Concatenating " + AWHOLELOTOFTIMES + " Strings..." );
		long	k2Time = me.kiaTwo();
		
		System.out.println("Concatenating " + AWHOLELOTOFTIMES + " buffers and turning " + 
				"each into a String...");
		long	k1Time = me.kiaOne();
		
		System.out.println("StringBuffer concat took " + k1Time + "ms");
		System.out.println("String concat took " + k2Time + "ms");
		if ( k1Time < k2Time ) {
			System.out.println ("Know it all #1 was correct.");
			System.out.println ("Build using a buffer first, then convert to a String.");
		} else {
			System.out.println ("Know it all #2 was correct.");
			System.out.println ("It is ok to simply concat a String.  No buf needed.");
		}
	}

	/**
	 * Concatenate a modestly long StringBuffer and convert to a String
	 * a whole bunch of times.
	 * @return The number of millis it took.
	 */
	private long	kiaOne () {
		

		long	elapsedTime = System.currentTimeMillis();
		StringBuffer longBuf = new StringBuffer();
		for ( long j = 0; j < AWHOLELOTOFTIMES; j++ ) {
			for ( long i = 0; i < SIZE; i++ ) {
				longBuf.append("a");
			}
			String aString = longBuf.toString();
			work(aString);
		}
		return elapsedTime = System.currentTimeMillis() - elapsedTime;
	}
	
	/**
	 * Simple concatenate to a String a whole bunch of times.
	 * @return The number of millis it took.
	 */
	private long	kiaTwo () {
		
		long	elapsedTime = System.currentTimeMillis();
		String longStr = new String();
		for ( long j = 0; j < AWHOLELOTOFTIMES; j++ ) {
			for ( long i = 0; i < SIZE; i++ ) {
				longStr = longStr + "a";
			}
			work(longStr);
		}
		return elapsedTime = System.currentTimeMillis() - elapsedTime;
	}
	
	/**
	 * In order to prevent the JIT from optimizing away our unused String, 
	 * let's use it for something stupid.
	 */
	private	void	work (String s) {
		// System.out.println("ss" + s);
		useless.add(s);
		useless.clear();
	}
}