JMAP 输出
[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。
原文链接：https://blog.csdn.net/lxb_champagne/article/details/18352945