Object creation in Java is slow

Question

My experience shows that object creation in Java is very slow. Often, I optimize my code by just removing object creation and using the same objects repeatedly.

I am wondering if its similarly slow in other language with OOP base, because, to me, it is very counter intuitive that a language that's hardcore object oriented, takes so much time for object creation.

Has anybody profiled this on several langauges?

Answer 1

While there might be a noticeable CPU impact under rare circumstances, in general object creation for current virtual machines is as fast as it can practically be.

Here is an article I like called "Urban performance legends", I think this is just one of those myths.

Also take a look at http://www.javaperformancetuning.com/tips/rawtips.shtml for ideas of how to performance tuning your Java App.

Regards.

Answer 2

Try see what you get from this - some exercising to try to get the VM to not optimize the loop away:

import java.util.ArrayList;
import java.util.Random;

class DummyInteger {
    private int i;
    public DummyInteger(int i) {
        this.i = i;
    }
    public int getI() {
        return i;
    }
}

public class ObjectCreationTest {

    final static int ITERATIONS = 2000000;
    public static void main(String[] args) {
        Random r = new Random(System.currentTimeMillis());

        int[] randArr = new int[ITERATIONS];
        for(int i = 0; i < ITERATIONS; i++) {
            randArr[i] = r.nextInt();
        }
        DummyInteger[] iArr = new DummyInteger[ITERATIONS];
        long start = System.currentTimeMillis();
        for(int i = 0; i < ITERATIONS; i++) {
            ArrayList<DummyInteger> list = new ArrayList<DummyInteger>(); 
            list.add(new DummyInteger(randArr[i]));
            iArr[i] = list.get(0);
        }
        long end = System.currentTimeMillis();
        System.out.println(String.format("Creating %d objects took %d ms",ITERATIONS*2,end-start));
        int sum = 0;
        for(DummyInteger mi: iArr) {
            sum += mi.getI();
        }
        System.out.println(sum);
        }
}

I got

Creating 4000000 objects took 678 ms

Which should be around 170 nanosecond per object.