Java中的字节默认情况下占用4个字节？ [英] Byte in Java Takes 4 bytes by default?

问题描述

可能重复：

内存中字节的大小 - Java

<我在一篇文章中读到了这篇文章。我只是按原样粘贴：

I read this in an article. I am just pasting as is:

• 该类占用至少8个字节。所以，如果你说 ** new Object（）; ** ，你将在堆上分配8个字节。


• 每个数据成员占用4个字节，除了long和double，占用8个字节。即使数据成员是一个字节，它仍然需要
  4字节！此外，使用的内存量在8
  字节块中增加。所以，如果你有一个包含一个字节的类，那么
  将占用该类的8个字节和8个字节的数据，总计16
  字节（呻吟！）。

• The class takes up at least 8 bytes. So, if you say **new Object();** you will allocate 8 bytes on the heap.
• Each data member takes up 4 bytes, except for long and double which take up 8 bytes. Even if the data member is a byte, it will still take up 4 bytes! In addition, the amount of memory used is increased in 8 byte blocks. So, if you have a class that contains one byte it will take up 8 bytes for the class and 8 bytes for the data, totalling 16 bytes (groan!).

这是真的Java字节分配/需要4个字节吗？而空类需要8个字节？
这里也很混乱。

Is it true Java byte allocates / takes 4 bytes? and empty class takes 8 bytes? Its confusing here as well.

推荐答案

这是假的，至少对于HotSpot JVM来说是错误的。在那里，类中的原始字节字段将占用一个字节，但是类的实例的大小确实从8个字节开始，并且字段被分组为每个占用8个字节的块 - 例如，您可以不要在8字节边界上分割字段。

That is false, at least for the HotSpot JVM. There, a primitive byte field in a class will take one byte, but it is true that the size of an instance of a class starts at 8 bytes, and fields are grouped into chunks that take eight bytes apiece -- for example, you can't split a field across an 8-byte boundary.

参见eg http://www.codeinstructions.com/2008/12/java -objects-memory-structure.html

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