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

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

2014年01月16日 11:00:12 lxb_champagne 阅读数：23002

JMAP 输出

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[hadoop@DEV logs]$ jmap -histo 24527 | head -30

 num     #instances         #bytes  class name
----------------------------------------------
   1:         31939       98883072  [C
   2:          8594        9461992  [B
   3:         30326        4256232  <constMethodKlass> 4: 30326 3892592 <methodKlass> 5: 2719 3226344 <constantPoolKlass> 6: 2450 1948704 <constantPoolCacheKlass> 7: 2719 1869200 <instanceKlassKlass> 8: 27599 662376 java.lang.String 9: 836 442968 <methodDataKlass> 10: 8215 394320 org.apache.tomcat.util.buf.ByteChunk 11: 3012 366720 java.lang.Class 12: 11257 360224 java.util.HashMap$Entry 13: 3417 273360 java.lang.reflect.Method 14: 6763 270520 java.util.TreeMap$Entry 15: 4326 260720 [S 16: 5410 259680 org.apache.tomcat.util.buf.MessageBytes 17: 6410 256400 org.apache.tomcat.util.buf.CharChunk 18: 4558 238352 [[I 19: 3347 211512 [Ljava.lang.Object; 20: 2144 189280 [I 21: 276 147936 <objArrayKlassKlass> 22: 948 142216 [Ljava.util.HashMap$Entry; 23: 2874 137952 java.util.HashMap 24: 621 89424 java.text.DecimalFormat 25: 2555 81760 java.util.concurrent.ConcurrentHashMap$HashEntry 26: 620 69440 java.util.GregorianCalendar 27: 1052 68936 [Ljava.lang.String;

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。

转自: https://blog.csdn.net/lxb_champagne/article/details/18352945