Java 8 forEach Stream() vs old forEach Loop

Question

I was trying a example code with spring. And a part of code is like below;

private List<Point> points;
long timeTakeninMilis = System.currentTimeMillis();

public List<Point> getPoints() {
    return points;
}

public void setPoints(List<Point> points) {
    this.points = points;
}

public void drawJava8() {
    points.stream().forEachOrdered(
            point -> System.out.println("Point : (" + point.getX() + ", "
                    + point.getY() + ")"));
    System.out.println("Total Time Taken drawJava8(): "
            + (System.currentTimeMillis() - timeTakeninMilis)
            + " miliseconds");
}

public void draw() {
    for (Point point : points) {
        System.out.println("Point = (" + point.getX() + ", " + point.getY()
                + " )");

    }
    System.out.println("Total Time Taken draw(): "
            + (System.currentTimeMillis() - timeTakeninMilis)
            + " miliseconds");
}

The OUTPUT,

  Jun 30, 2015 11:30:53 AM org.springframework.context.support.ClassPathXmlApplicationContext prepareRefresh
  INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@7daf6ecc: startup date [Tue Jun 30 11:30:53 IST 2015]; root of context hierarchy
  Jun 30, 2015 11:30:53 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
  INFO: Loading XML bean definitions from class path resource [spring.xml]
  Point = (0, 0 )
  Point = (-50, 0 )
  Point = (0, 50 )
  Total Time Taken draw(): 70 miliseconds
  Point : (0, 0)
  Point : (-50, 0)
  Point : (0, 50)
  Total Time Taken drawJava8(): 124 miliseconds
  Jun 30, 2015 11:30:54 AM org.springframework.context.support.ClassPathXmlApplicationContext doClose
  INFO: Closing org.springframework.context.support.ClassPathXmlApplicationContext@7daf6ecc: startup date [Tue Jun 30 11:30:53 IST 2015]; root of context hierarchy

Why it is taking more time? Or i am doing something wrong?

I was expecting it to be faster or of similar speed... Please help me understand what is the benefit of the Lambda Expressions?

INFO: I did it in two different programs. Times are taken from those. I merged them here to make it short.

By looking your output you are calling drawJava() first and drawJava8() later. Are you resetting the variable timeTakeninMilis with the current time before calling drawJava8()? — Madhavi Balan
– Madhavi Balan, Commented Jun 30, 2015 at 6:30
Writing a benchmark for java is hard; the jvm is continutally analysing your code and optimising it. Have a look at stackoverflow.com/questions/504103/… — beresfordt
– beresfordt, Commented Jun 30, 2015 at 6:34
@Madhavi Balan: I did it in two different program. Just merged them while posting so that it will be short as they are simple programs. — Rajkishan Swami
– Rajkishan Swami, Commented Jun 30, 2015 at 6:40
Did you try forEach instead of forEachOrdered ? But as @beresfordt said: Benchmarking is not that easily done. One step closer to a valid result would be to use much more points and to run the test many many times, so you have some statistical value. All you can say now is that this one single time, execution of the java 8 method was much slower. But this could have more reasons than the code itself. — Fildor
– Fildor, Commented Jun 30, 2015 at 6:53
@beresfordt : Wow... a lot of useful information that thread have. Thank you very much. — Rajkishan Swami
– Rajkishan Swami, Commented Jun 30, 2015 at 6:53

ring bearer · Accepted Answer · 2015-07-01 05:38:09Z

3

Adding this as an analysis per original poster's request.

We can not really predict the sophisticated analysis and transformation that the modern JIT compiler performs on running code. Hence while benchmarking items such as these, you should not conclude it just by running two method calls.

Instead, create various sample input sets (boundary cases) and check the perofmance by repeatedly calling your test cases without shutting down JVM. In this case for example :

for (int i=0;i<100;i++){draw(); drawJava8();}

Once you have the results, find out average execution and you can safely ignore first execution result as it might not have had optimizations.

So the conclusion you have drawn from your tests is not completely correct.

edited Jul 1, 2015 at 5:38

answered Jun 30, 2015 at 7:25

ring bearer

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1 Comment

phoenixSid Over a year ago

this is brilliant!

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