jmap -histo pid 输出的[C [B [I [S methodKlass constantPoolKlass含义

 

Heap Histogram

All Classes (excluding platform)

Class	Instance Count	Total Size
class [I	10295	74101376
class [B	37484	20206389
class [C	77031	9857592
class [Ljava.lang.Object;	18232	1935080
class java.lang.String	70031	1400620
class [Ljava.util.HashMap$Entry;	7156	1344856
class java.lang.reflect.Method	6986	901194
class java.util.HashMap$Entry	25634	717752
class java.lang.Class	4535	653040
class [S	9082	617178
class java.nio.HeapByteBuffer	9998	389922
class java.nio.HeapCharBuffer	9736	360232
class [Ljava.lang.String;	4306	330664
class java.util.HashMap	6454	309792
class java.lang.reflect.Field	2181	229005
class [Ljava.util.Hashtable$Entry;	644	185440
class [Ljava.lang.Class;

 

 

其中：

 

[C is a char[]
[S is a short[]
[I is a int[]
[B is a byte[]
[[I is a int[][]

 

上面的输出中[C对象占用Heap这么多，往往跟String有关，String其内部使用final char[]数组来保存数据的。

 

constMethodKlass/ methodKlass/ constantPoolKlass/ constantPoolCacheKlass/ instanceKlassKlass/ methodDataKlass

与Classloader相关，常驻与Perm区。