What is the meaning of the information that I get by printing an Object in Java? [duplicate]

This question already has answers here: 开发者_运维技巧 How do I print my Java object without getting "SomeType@2f92e0f4"? (13 answers) Closed 5 years ago.

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 !

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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())

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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.

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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

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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.

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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().