While debugging java app what information is shown for a variable in a stack frame [duplicate]

Question

When I debug java app in Intellij Idea I see all variables in a stack frame like this:

object={java.lang.Object@77}

What does the number after "@" mean? It is different from what hashCode returns. hashCode returns number 2a134eca in hex representation which equals to 705908426 in integer representation. Numbers 77 and 705908426 are distinct.

Answer 1

The @ is the object count number since the app started. So @1012 means the 1012th object created since the app started.

It is not the identity hashcode.

Here is some proof: (I say this because I don't actually know, but I observed it)

public static void main(String [] args) throws Throwable {

    Object object = new Object();
    Object object1 = new Object();
    Integer foo = new Integer(5);
    Object object2 = new Object();
    String str = new String("bar");

    System.out.println("code :" + System.identityHashCode(object));

    RuntimeException exception = new RuntimeException();
    exception.printStackTrace(); //put breakpoint here


}

Output: code :789451787 code :java.lang.Object@2f0e140b

789451787=2f0e140b By the way...

Output from IntelliJ Debugger:

static = org.boon.core.MyClass
args = {java.lang.String[0]@**97**}
object = {java.lang.Object@**98**}
object1 = {java.lang.Object@**99**}
foo = {java.lang.Integer@**100**}"5"
object2 = {java.lang.Object@**101**}
str = {java.lang.String@**102**}"bar"
exception = {java.lang.RuntimeException@**103**}"java.lang.RuntimeException"

I know this empirically, but I don't know the actual implementation, but I think it is related to issues like this:

as3: meaningful object identification while debugging.

Answer 2

What does the number after "@" mean?

@ is just a separator

Debuggers use the toString method of an object to display its value. And here is description of default implementation of toString method from the javadocs:

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())