blocks|key|917074|text|从Java1.4到Java6，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|917075|垃圾收集的行为方式有变化吗？|blockquote|917076|917077|917078|一定!|917079|从Java1.4到Java6是一个相当长的时间跨度(根据this+wiki+article的说法，从initial+releases到initial+1.4+release到the+current+Java+6+release几乎有5年的时间，超过8年的时间)。|offset|length|917080|在这段时间内应用了许多更改和优化，只要您的程序仍然可以工作，您就不应该真正关心。|917081|拥有更多的已用内存只意味着JVM不会在不需要的时候浪费时间进行垃圾收集。如果您希望它使用更少的内存，那么您应该减少最大堆(或者调整JVM参数；this+article解释了如何在Java5中做到这一点，许多建议仍然适用)。|917082|如果你真的得到了以前没有得到的OutOfMemoryError，那就有点不同了。然后，您应该检查如何使用弱引用和软引用，或者作为最后的手段，尝试找出是否遇到了JVM错误。|style|CODE|917083|entityMap|0|LINK|mutability|MUTABLE|url|http://en.wikipedia.org/wiki/Java_version_history|1|http://en.wikipedia.org/wiki/Java_version_history#J2SE_1.4_.28February_6.2C_2002.29|2|http://en.wikipedia.org/wiki/Java_version_history#Java_SE_6_.28December_11.2C_2006.29|3|4|http://en.wikipedia.org/wiki/Java_version_history#Java_SE_6_Update_21|5|http://www.oracle.com/technetwork/java/gc-tuning-5-138395.html^0|0|0|0|0|0|S|H|0|1E|7|1|1M|8|2|1V|J|3|2F|Q|4|0|0|1Z|C|5|0|F|G|0^^$0|@$1|2|3|4|5|6|7|1B|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1C|8|@]|9|@]|A|$]]|$1|E|3|-4|5|6|7|1D|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|1F|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|1G|8|@]|9|@$K|1H|L|1I|1|1J]|$K|1K|L|1L|1|1M]|$K|1N|L|1O|1|1P]|$K|1Q|L|1R|1|1S]|$K|1T|L|1U|1|1V]]|A|$]]|$1|M|3|N|5|6|7|1W|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1X|8|@]|9|@$K|1Y|L|1Z|1|20]]|A|$]]|$1|Q|3|R|5|6|7|21|8|@$K|22|L|23|S|T]]|9|@]|A|$]]|$1|U|3|-4|5|6|7|24|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]|12|$5|X|Y|Z|A|$10|13]]|14|$5|X|Y|Z|A|$10|15]]|16|$5|X|Y|Z|A|$10|13]]|17|$5|X|Y|Z|A|$10|18]]|19|$5|X|Y|Z|A|$10|1A]]]]

<blockquote>
 did the way garbage collection behaves changed from Java 1.4 to Java 6?
</blockquote>

Definitely!

Java 1.4 to Java 6 is a pretty long timespan (almost 5 years between the <a href="http://en.wikipedia.org/wiki/Java_version_history#J2SE_1.4_.28February_6.2C_2002.29" rel="nofollow noreferrer">initial</a> <a href="http://en.wikipedia.org/wiki/Java_version_history#Java_SE_6_.28December_11.2C_2006.29" rel="nofollow noreferrer">releases</a> and more than 8 years between the <a href="http://en.wikipedia.org/wiki/Java_version_history#J2SE_1.4_.28February_6.2C_2002.29" rel="nofollow noreferrer">initial 1.4 release</a> and <a href="http://en.wikipedia.org/wiki/Java_version_history#Java_SE_6_Update_21" rel="nofollow noreferrer">the current Java 6 release</a>, according to <a href="http://en.wikipedia.org/wiki/Java_version_history" rel="nofollow noreferrer">this wiki article</a>).

Many changes and optimizations are applied in that time and you should not really care as long as your program still works.

Having more used memory only means that the JVM doesn't waste time with garbage collection when it doesn't need to. If you want it to use less memory, then you should reduce the maximum heap (or otherwise tweak the JVM parameters; <a href="http://www.oracle.com/technetwork/java/gc-tuning-5-138395.html" rel="nofollow noreferrer">this article</a> explains how to do that in Java 5, much of the advice is still applicable).

It's somewhat different if you actually get <code>OutOfMemoryError</code> that you didn't get previously. Then you should check how you use weak and soft references or as a last resort try to find out if you hit a JVM bug.

blocks|key|1663160|text|在1.4和5之间以及5和6之间，已经对垃圾收集进行了几次优化。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1663161|Oracle/Sun在线提供了一些关于性能差异的白皮书：|1663162|Java+5+Performance+White+Paper|offset|length|1663163|Java+6+Performance+White+Paper|1663164|entityMap|0|LINK|mutability|MUTABLE|url|https://web.archive.org/web/20070206025504/http://java.sun.com/performance/reference/whitepapers/5.0_performance.html#2.11|1|https://www.oracle.com/java/technologies/javase/6performance.html#2.2^0|0|0|0|U|0|0|0|U|1|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|V|8|@]|9|@$F|W|G|X|1|Y]]|A|$]]|$1|H|3|I|5|6|7|Z|8|@]|9|@$F|10|G|11|1|12]]|A|$]]|$1|J|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q]]|R|$5|M|N|O|A|$P|S]]]]

There have been several optimizations on garbage collecting between 1.4 and 5 and between 5 and 6.
Oracle/Sun have some whitepapers on the performance differences online:
<a href="https://web.archive.org/web/20070206025504/http://java.sun.com/performance/reference/whitepapers/5.0_performance.html#2.11" rel="nofollow noreferrer">Java 5 Performance White Paper</a>
<a href="https://www.oracle.com/java/technologies/javase/6performance.html#2.2" rel="nofollow noreferrer">Java 6 Performance White Paper</a>

blocks|key|2795738|text|Java+SE在8年内发生了很大变化。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2795739|关于垃圾收集器，Java+SE+6已经改进了很多。在JavaSE6Update14中引入了新的Garbage+First+GC。|offset|length|2795740|entityMap|0|LINK|mutability|MUTABLE|url|http://java.sun.com/performance/reference/whitepapers/6_performance.html#2.2|1|http://blogs.oracle.com/theplanetarium/entry/java_vm_trying_a_new^0|0|8|9|0|1B|D|1|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@$D|R|E|S|1|T]|$D|U|E|V|1|W]]|A|$]]|$1|F|3|-4|5|6|7|X|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]|N|$5|I|J|K|A|$L|O]]]]

Java SE changed a lot in 8 years.

Concerning the garbage collector, it has been improved a lot with <a href="http://java.sun.com/performance/reference/whitepapers/6_performance.html#2.2" rel="nofollow noreferrer">Java SE 6</a>.
In Java SE 6 Update 14 the new <a href="http://blogs.oracle.com/theplanetarium/entry/java_vm_trying_a_new" rel="nofollow noreferrer">Garbage First</a> GC was introduced.

We have recently upgraded one of our applications from Java 1.4 to Java 6.

With some load &amp; performance tests, we observed that available memory stayed in general at much lower levels in Java 6 than at what it used to be with Java 1.4.

After some profiling on the app with Java 6, we noticed that many objects no longer referenced by any other objects (i.e. candidates for garbage collection) stayed in memory and were apparently never garbage collected. We took that as the explanation for the lower available memory. 

Question is: did the way garbage collection behaves changed from Java 1.4 to Java 6?

Garbage collection change from Java 1.4 to Java 6?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我们最近将我们的一个应用程序从Java 1.4升级到了Java 6。通过一些负载和性能测试，我们观察到，与Java1.4相比，Java 6中的可用内存通常处于更低的水平。在使用Java6对应用程序进行了一些分析之后，我们注意到许多不再被任何其他对象引用的对象(即垃圾回收的候选对象)留在内存中，显然从未被垃圾回收过。我们将此作为较低可用内存的解释。问题是:垃圾收集的行为方式是否从Java 1.4更改

问垃圾收集从Java1.4到Java6的变化？
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