Please help with the following question. Assume that I have class that contains only methods. Will space in heap be allocated for objects created of this class? If yes then what does it contain?
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Please see the answers here - stackoverflow.com/questions/258120/…Fairoz– Fairoz2017-06-05 15:09:14 +00:00Commented Jun 5, 2017 at 15:09
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The question linked by Fairoz contains most relevant data, but I'll try to narrow information to your case.
Yes. The JVM will take a contiguous space off the heap to store these objects.
The contents are specific to the JVM implementation. In HotSpot, you can see the specifics in the source code.
- There will be a machine word called "Mark", which is defined here, and is used to keep the hashCode, locking state, and garbage collection. This takes 8 bytes.
- Next will be a pointer to the Klass, which contains information about the class, such as methods.
If you're in a 64 bit JVM, with compressedOops enabled (as is default on java 8) the Klass pointer will take only 4 bytes. Since you have no fields, the total size is 12 bytes. However, the JVM forces to align to a full word, so your object will use 4 bytes for padding. In total, 16 bytes.
Some useful documentation: - https://www.infoq.com/articles/Introduction-to-HotSpot - https://psy-lob-saw.blogspot.com.es/2013/05/know-thy-java-object-memory-layout.html
