问题
Lets say i have this code :
Integer[] a= new Integer[5];
System.Out.println(((Object)a).toString());
the output is get is
[Integer@89fbe3
what is the meaning of 89fbe3 ? is this some kind of address ? hash code? is it unique for each object? , and if so- if its a multi-threaded program , is it still unique ?
thanks !
回答1:
It's the memory address of the object which is what the default toString() implemented in the Object class does. It is also the default hashCode().
回答2:
It's the result of System.identityHashCode(Object x);
which is the default implementation of every object's hashCode()...
from the Object javadoc:
getClass().getName() + '@' + Integer.toHexString(hashCode())
回答3:
The 89fbe3 is a hex version of the hash code. The [I means an array of ints (I'm surprised you get that with an Integer[], are you sure it wasn't an int[]?)
Some others:
[L<typename>;: an array of reference type "typename" (e.g.[Ljava.lang.Integer)[J: an array of longs[B: an array of bytes
etc.
回答4:
It is the identity hash code of the object (you can think of it as the address of the object), along with some type information.
[ = array I = Integer
回答5:
I think that while technically all the answers are correct, the real answer is "NO". This number has no meaning and you can make absolutely no assumptions about it.
来源：https://stackoverflow.com/questions/4696103/what-is-the-meaning-of-the-information-that-i-get-by-printing-an-object-in-java