Why Java doesn't have `inline` methods?

Question

Inline methods (like in C++) seem to be a very simple idea and help to optimize code.
For example (averaged over 1'000'000 cycles):

float dx = a - c, dy = b - d;
float distance = (float) Math.sqrt(dx * dx + dy * dy);

is 4(!) times faster then calling method with the same content:

   float distance = getDistance(a,b,c,d);

So there must be a reason that Java doesn't support inline methods.
What is it?

As far as I know inlining is typically done by the JVM at execution time — Rahul Tripathi, Apr 22 '15 at 10:09
Java works on JVM. It supports many optimizations techniques in runtime, include method inlining: https://wikis.oracle.com/display/HotSpotInternals/PerformanceTechniques. — injecto, Apr 22 '15 at 10:14

Aaron Digulla · Accepted Answer · 2015-04-22T10:14:59.490

4

I don't see a reason why this happens. Try to the method final and the difference should go away. And use the latest version of Java from Oracle or IBM.

Now the reason why Java doesn't have many optimization keywords is simple: The people who invented Java didn't like how much time C developers spent to squeeze out the last drop of juice out of the compiler. That felt like a huge waste of productive time.

So the idea with Java is that you write code. You concentrate just on writing good code. The Java compiler and the runtime then make it fast. That means that the runtime analyzes the CPU and optimizes the code differently depending on what the CPU can do. This is why Java code can be faster than C++.

Of course, bad code is bad, no matter how clever the optimizer is. So you can write code which very slow but that doesn't depend on the language.

edited Apr 22 '15 at 10:14

answered Apr 22 '15 at 10:09

Aaron Digulla

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Correct me if I am missing something but JVM expert Brian Goetz says final has no impact on methods being inlined. Reference: http://www.ibm.com/developerworks/java/library/j-jtp1029/index.html – Rahul Tripathi Apr 22 '15 at 10:12
@RahulTripathi: I don't see another reason why the inlined code should be slower. Do you? – Aaron Digulla Apr 22 '15 at 10:13
Neither do I but I got confused after going through this, thats why I asked! – Rahul Tripathi Apr 22 '15 at 10:14
`Of course, bad code is bad, no matter how clever the optimizer is.`..I like that. +1 – Rahul Tripathi Apr 22 '15 at 10:15
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@RahulTripathi: I tried to improve the wording. – Aaron Digulla Apr 22 '15 at 10:15

Why Java doesn't have `inline` methods?

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