Java 1.6与C ++的性能如何？

Question

With Java 1.6 out can we say that performance of Java 1.6 is almost equivalent to C++ code or still there is lot to improve on performance front in Java compared to C++ ?

Thanks.

Answer 1

Debian likes to conduct benchmarks on this sort of thing . In their case, it appears that Java is about half as fast and consumes 2-18 times as much memory as C++.

Answer 2

A well-written Java program is never going to be as fast as a well-written C or C++ program. The virtual machine is an irreducible overhead. However, most code is not well written.

Java is a simpler language than C++, and offers a more forgiving environment for inexperienced programmers - so if your programmers are inexperienced (and cheap), then Java will probably perform 'better' than C++.

shared_ptr s offer a similarly forgiving environment in C++, so they are very tempting for inexperienced programmers, or those migrating from Java, But their performance overhead is as bad or worse than Java's garbage collection. I've seen large C++ programs where every variable is a shared_ptr , and they perform terribly.

My opinion

Personally, I think that large projects need to choose an 'easy' programming language for the bulk of their code, and a 'fast' one for sections that need optimising. Java may be a good choice for the 'easy' language, especially since there is currently a plentiful supply of Java programmers - in the future, I think even easier languages such as Python will begin to take over.

C++ is a reasonable choice for a 'fast' language if you already know it, but I think it's over-complexity will eventually see it fall by the wayside, while C will continue to fulfill this role.

Answer 3

I would expect that most of the time for most applications C++ will be faster than Java.

In some cases there will be some C++ which is slower than Java for a given task. This is pretty rare and always a result for poor implemntation or more commenly poor refactoring of an application.

In the majority of cases the performance difference more than offset by the fexibility, ease of use, availability of libraries, and, portability that Java provides.

In a very few cases performance is so critical that developing in Java would be a poor choice <opinion><flame off>in these cases plain C is usually a better choice than C++ </flame></opinion>.

Currently the sweetspot in performance/ease of use/ease of development tradeoffs is C#. Portability is a big issues here though.

Answer 4

I find that Java performs very well.

However, why has no one ever fixed my biggest complaint?

Java uses FIVE TIMES as much memory as a C++ program doing the same job. At least!

And once it's used, Java keeps it !

Please, please, why won't anyone write a garbage collector for Java that uses minimum amounts of RAM? It could compact the heap and returns the memory to the OS. Instead of ridiculous piles of -Xm* options, use the memory needed and then give it back !

Actually I am sure some of the embedded system JVMs do this, but none of the desktop or server systems do.

This memory piggishness makes Java applications all want to act as if they own the entire computer system, that no one ever wants to run more than one application and that RAM is free and infinitely upgradable.

Therefore, no matter how great the performance, I would never write anything like a utility program in Java. Only gigantic server apps need apply.

Answer 5

What program are you developing?

Comparing C++ to Java speed is like comparing a screwdriver and a hammer, pointless. In the world we live in, where both supercomputers and toasters need to be programmed, you need to focus on your particular requirements.

I use C++ for hard realtime software running on embedded systems. I wouldn't dream of using the awfully broken Java for realtime spec for at least another 5 years, when it will hopefully be mature. I would be equally loath to use C++ for a database, cloud accessing middleware app (actually I have no Idea what I just said, but I know Java is good for 'that sort of stuff')

Would you use a ferrari with no trunk space to move your belongings? Would you bring a minivan to a drag race?

People have to understand that just because they are programming languages, does not mean they are comparable in a meaningful way.

Answer 6

不会。除非你测量它，否则你可能不会说出来。

Answer 7

Performance is usually "good enough" for most purposes. The question is what you want to compare exactly, and if you have applied a profiler to find and fix the hotspots in your code.

JVM's based on Sun's code still pay a hefty startup-tax (I still wonder why they cannot snapshot that and restart from there) but Suns approach has been correctness first, speed second, and it's taken them 10 years to get up to par.

So the answer is "It depends" :)

Answer 8

For most applications it is almost certainly possible to write a C++ program which performs considerably better than a program to achieve the same thing in java.

However if the program isn't optimised for speed then java will likely be just as fast or faster because the compiler / JIT is able to make optimisations that a C++ environment can't.

Basically if you are willing to spend considerable time understanding and coding for performance you can probably do a considerably better job in c++ eventually than you could in java but for the same amount of time and effort it is quite likely that java will "win".

As usual though, algorithmic improvements tend to make as much if not more difference than the language.