Java – the concurrent mark-sweep generation in the heap

garbage-collectionjava

In the following output, what is the concurrent mark-sweep generation?

par new generation   total 24512K, used 12082K [0x00007fb3b9420000, 0x00007fb3bac20000, 0x00007fb3bac20000)
 eden space 24448K,  49% used [0x00007fb3b9420000, 0x00007fb3b9fec808, 0x00007fb3bac00000)
 from space 64K,   0% used [0x00007fb3bac10000, 0x00007fb3bac10000, 0x00007fb3bac20000)
 to   space 64K,   0% used [0x00007fb3bac00000, 0x00007fb3bac00000, 0x00007fb3bac10000)
concurrent mark-sweep generation total 8364032K, used 233100K [0x00007fb3bac20000, 0x00007fb5b9420000, 0x00007fb5b9420000)
concurrent-mark-sweep perm gen total 98304K, used 72031K [0x00007fb5b9420000, 0x00007fb5bf420000, 0x00007fb5bf420000)

I understand eden, from, to and perm gen, but what is "concurrent mark-sweep generation"?

Best Answer

"concurent mark-sweep generation" is the old generation.

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One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn't be as easy if you were using Hashtable.

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The official tutorial may be of some use to you.

	Class	Package	Subclass (same pkg)	Subclass (diff pkg)	World
`public`	+	+	+	+	+
`protected`	+	+	+	+
no modifier	+	+	+
`private`	+

+ : accessible
blank : not accessible

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