What does the class class [B represents in Java?

Question

I am trying out a tool jhat here to test my java memory usage. It reads in a heap dump file and prints out information as html. However, the tables shows as follows:

Class Instance Count Total Size 
class [B  36585  49323821  
class [Lcom.sun.mail.imap.IMAPMessage;  790  16254336  
class [C  124512  12832896  
class [I  23080  11923504  
class [Ljava.lang.Object;  13614  6664528  
class java.lang.String  108982  2179640  
class java.lang.Integer  219502  878008

What are those [B [C etc classes?

http://stackoverflow.com/questions/1040868/java-syntax-and-meaning-behind-b1ef9157-binary-address — erickson, Sep 23 '09 at 15:12

score 133 · Accepted Answer · edited Apr 24 '18 at 00:04

133

Those are arrays of primitives ([B == byte[], [C == char, [I == int). [Lx; is an array of class type x.

For a full list:

[Z = boolean
[B = byte
[S = short
[I = int
[J = long
[F = float
[D = double
[C = char
[L = any non-primitives(Object)

Also see the Javadoc for Class.getName.

edited Apr 24 '18 at 00:04

user2357112

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answered Sep 23 '09 at 14:51

Aaron Digulla

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[J means ? [S means ? – Chinaxing Mar 09 '15 at 01:54
See http://stackoverflow.com/a/12505922/34088 for a full list or http://docs.oracle.com/javase/tutorial/reflect/special/arrayComponents.html to determine the type for yourself. – Aaron Digulla Mar 10 '15 at 12:33

score 2 · Answer 2 · answered Sep 23 '09 at 14:51

2

Looks like an array of characters (C)/bytes (B)/ints (I).

answered Sep 23 '09 at 14:51

Rob Di Marco

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What does the class class [B represents in Java?

2 Answers2

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