micro.java

import java.util.Date;
import java.util.HashMap;
import java.math.*;


// for futures, compare to Go
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.Callable;

public class micro {

	public static void t1() {

		// the first pass uses standard LONGs

		long t0 = new Date().getTime();

		long x = 10;

		// odd, increasing the loop size an order of magnitude doesn't increase
		// the runtime
		for (int i=0; i < 1000000; i++) {
			x = ( 2 * x ) + x + 1 ;
		}

		// the second pass uses BigInteger, which will give a more correct answer
		// python is equivlent
		long t1 = new Date().getTime();

		BigInteger x_b = new BigInteger("10");
		BigInteger two = new BigInteger("2");

		for (int i=0; i < 100000; i++) {
			BigInteger x2_b = x_b.add( BigInteger.ONE );
			BigInteger x3_b = x_b.multiply(two);
			x_b = x2_b.add(x3_b);
		}

		long t2 = new Date().getTime();

		System.out.printf("t1: time1 long %.3f time2 BigInteger %.3f \n", 
			(float) (t1-t0) / 1000.0, (float) (t2 - t1) / 1000);

	}

	public static void t2() {

		long t0 = new Date().getTime();

		final int nStrings = 1000;
		final int nCats = 100000;

		// make some strings
		String[] a1 = new String[nStrings];
		int c = 'a';
		a1[0] = Integer.toString(c);
		for (int i=1; i < nStrings; i++) {
			c++;
			a1[i] = a1[i-1] + Integer.toString(c);
		}

		long t1 = new Date().getTime();

		// using +
		String[] a2 = new String[nCats];
		for (int i=0; i < nCats; i++) {
			a2[i] = a1[i % a1.length ] + 
					a1[ (i+7) % a1.length ] + 
					a1[ (i+17) % a1.length ] + 
					a1[ (i+27) % a1.length ] +
					a1[ (i+37) % a1.length ] + 
					a1[ (i+47) % a1.length ] +
					a1[ (i+57) % a1.length ];
		}

		long t2 = new Date().getTime();

		// using stringbuilder
		String[] a3 = new String[nCats];
		for (int i=0; i < nCats; i++) {
			StringBuilder sb = new StringBuilder(1000); // just a guess
			sb.append( a1[ i % a1.length ] );
			sb.append( a1[ (i+7) % a1.length ] );
			sb.append( a1[ (i+17) % a1.length ] );		
			sb.append( a1[ (i+27) % a1.length ] );		
			sb.append( a1[ (i+37) % a1.length ] );
			sb.append( a1[ (i+47) % a1.length ] );
			sb.append( a1[ (i+57) % a1.length ] );
			a3[i] = sb.toString();

		}

		long t3 = new Date().getTime();

		System.out.printf("t2: arraycreate time %.3f cat1 time %.3f cat2 time %.3f \n", 
			(float) (t1-t0) / 1000.0, (float) (t2-t1) / 1000.0, (float) (t3-t2) / 1000.0);

	}


	public static void t5() {

		long t0 = new Date().getTime();

		for (int x=0; x < 1000000; x++) {
			HashMap<Integer, String> a = new HashMap<Integer, String>();
			for (int a1=0; a1 < 50; a1++) {
				a.put(a1, Integer.toString(a1) );
			}
		}

		long t1 = new Date().getTime();

		System.out.printf("f5: %.3f \n", (float) (t1-t0) / 1000.0);

	}

    public static void main(String[] args) {
        System.out.println("java microbenchmark");
        t1();
        t2();
        t5();
    }

}