Memory address of variables in Java

Question

Please take a look at the picture below  When we create an object in java with the new keyword  we are getting a memory address from the OS   When we write out println objName  we can see a  special  string as output  My questions are    What is this output  If it is memory address which given by OS to us   a  How can I convert this string to binary   b  How can I get one integer variables address

User · Answer

this is useful to know about hashcode in java    http   eclipsesource com blogs 2012 09 04 the-3-things-you-should-know-about-hashcode

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In Java when you are making an object from a class like Person p   new Person     p is actually an address of a memory location which is pointing to a type of Person   When use a statemenet to print p you will see an address  The new key word makes a new memory location containing all the instance variables and methods which are included in class Person and p is the reference variable pointing to that memory location

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What you are getting is the result of the toString   method of the Object class or  more precisely  the identityHashCode   as uzay95 has pointed out    When we create an object in java with new keyword  we are getting a memory address from the OS    It is important to realize that everything you do in Java is handled by the Java Virtual Machine  It is the JVM that is giving this information  What actually happens in the RAM of the host operating system depends entirely on the implementation of the JRE

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That is the output of Object s  toString    implementation   If your class overrides toString    it will print something entirely different

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Like Sunil said  this is not memory address This is just the hashcode  To get the same   content  you can   If hashCode is not overridden in that class         Integer toHexString obj hashCode      If hashCode is overridden  you get the original value with         Integer toHexString System identityHashCode obj      This is often confused with memory address because if you don t override hashCode    the memory address is used to calculate the hash

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That is the class name and System identityHashCode   separated by the     character  What the identity hash code represents is implementation-specific  It often is the initial memory address of the object  but the object can be moved in memory by the VM over time  So  briefly  you can t rely on it being anything   Getting the memory addresses of variables is meaningless within Java  since the JVM is at liberty to implement objects and move them as it seems fit  your objects may will move around during garbage collection etc    Integer toBinaryString   will give you an integer in binary form

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This is not memory address This is classname hashcode Which is the default implementation of Object toString   public String toString         return getClass   getName      quot   quot    Integer toHexString hashCode        where Class name   full qualified name or absolute name  ie package name followed by class name  hashcode   hexadecimal format  System identityHashCode obj  or obj hashCode   will give you hashcode in decimal format   Hint  The confusion root cause is that the default implementation of Object hashCode   use the internal address of the object into an integer  This is typically implemented by converting the internal address of the object into an integer  but this implementation technique is not required by the Java    programming language   And of course  some classes can override both default implementations either for toString   or hashCode   If you need the default implementation value of hashcode   for a object which overriding it  You can use the following method System identityHashCode Object x

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It is possible using sun misc Unsafe   see this great answer from  Peter Lawrey -  Is there a way to get a reference address   Using its code for printAddresses          public static void printAddresses String label  Object    objects        System out print label      0x        long last   0      int offset   unsafe arrayBaseOffset objects getClass         int scale   unsafe arrayIndexScale objects getClass         switch  scale        case 4          long factor   is64bit   8   1          final long i1    unsafe getInt objects  offset   amp  0xFFFFFFFFL    factor          System out print Long toHexString i1            last   i1          for  int i   1  i  lt  objects length  i                  final long i2    unsafe getInt objects  offset   i   4   amp  0xFFFFFFFFL    factor              if  i2  gt  last                  System out print         Long toHexString i2 - last                else                 System out print    -    Long toHexString  last - i2                last   i2                    break      case 8          throw new AssertionError  Not supported              System out println        I set up this test          hashcode     System out println  Hashcode           myObject hashCode         System out println  Hashcode           System identityHashCode myObject        System out println  Hashcode  HEX      Integer toHexString myObject hashCode             toString     System out println  toString           String valueOf myObject         printAddresses  Address   myObject     Here is the output    Hashcode         125665513 Hashcode         125665513 Hashcode  HEX    77d80e9 toString         java lang Object 77d80e9 Address  0x7aae62270   Conclusion     hashcode    address toString   class HEX hashcode

[java] Memory address of variables in Java

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