Possible Duplicate:
What’s the implementation of hashCode in java Object?
While I was browsing through the Object class, I found that there is only a declaration of the hashCode() method. Where is the implementation part? If there is no implementation how does the hashCode() method return me a result?
It's implemented in the native code. As for implementation, it's a bit more tricky - you can alter default implementation. If you look at the "Open JDK" sources you will see the following options:
-XX:hashCode=n (from 0 to 5).
- 0 – Park-Miller RNG (default)
- 1 – function of address and some global state
- 2 – const 1
- 3 – sequenatial counter
- 4 – address of an object
- 5 – thread specific xor-shift
You can find a detailed implmenetation here: http://hg.openjdk.java.net/jdk7/jdk7/hotspot/file/tip/src/share/vm/runtime/synchronizer.cpp
Consider source code and comments of static inline intptr_t get_next_hash() function.
The native keyword indicates that it has been implemented in native code (the JVM).
If you see the declaration of hashcode
public native int hashCode();
native in declaration indicates that it is implemented natively in jvm code.
Where is the implementation part?
It's implemented by the framework already. Please see the documentation.
If there is no implementation how does the hashCode() method return me a result?
However, if you create a custom type you are responsible for generating an int value that is a good representation of the objects current state. Here is a good example of that.
来源：https://stackoverflow.com/questions/14521756/how-hashcode-method-in-object-class-is-implemented