what is the number that it shows when I print out the this pointer in java?

Question

This program

public class HelloWorld{
    public void testFunc(){
        System.out.println("Class = "+this);
    }

    public static void main(String[] args){
        HelloWorld hw = new HelloWorld();
        System.out.println("Hello, World");
        hw.testFunc();
    }
}

gives me this output:

Hello, World
Class = HelloWorld@7c6768

What does @7c6768 after HelloWorld in the second line mean?

It returns the toString() of the object. If not overidden, that will be classname@hashcode in hexa — Michael Laffargue, Jul 26 '13 at 10:04
@KanagarajM not of the _class_, but of that _instance_ of the class. — jlordo, Jul 26 '13 at 10:05

score 13 · Answer 1 · answered Jul 26 '13 at 10:03

13

Object's toString() is implemented as follows:

public String toString() {
    return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

Since your HelloWorld class doesn't override it, this is the method called.

answered Jul 26 '13 at 10:03

jlordo

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I'm sorry but I want to ask a very basic question that I just seem to understand: In your code when you say `getClass().getName()`, which class do getClass() and getName() belong to? Is getClass()a member function of the class in which this toString() function is defined? If so then where does getName() come from? – user13267 Jul 26 '13 at 10:09
Every class in Java extends `Object`, see http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html That's why every class also has the `getClass()` method. – jlordo Jul 26 '13 at 10:11

score 9 · Answer 2 · edited Jul 28 '13 at 16:01

The toString() method returns a string representation of the object.

In general, the toString() method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

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())

Suresh Atta · Accepted Answer · 2013-07-26T12:28:42.437

As per Docs of toString() method in Object class

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:

When

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

When you call toString() on object ,If you ovveride like below ,you get your own implementation

 @Override
  public String toString() {
     //return something 
  }

Otherwise gives the default implementation,which you are seeing right now

From Object class Source code

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

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())

Returns:
a string representation of the object.


    public String  toString() {
         return getClass().getName() + "@" + Integer.toHexString(hashCode());
     }

I just wanted to add: you can override the toString() method in that object in order to print something more meaningful. — Lenymm, Jul 26 '13 at 10:04
Yeah if I define a function as `@Override public String toString(){ return "TEST"; } ` it shows me TEST instead of the default value. — user13267, Jul 26 '13 at 10:12

score 3 · Answer 4 · answered Jul 26 '13 at 10:03

3

From the API:

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

answered Jul 26 '13 at 10:03

morgano

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ThiepLV · Answer 5 · 2013-07-26T10:12:34.720

3

HelloWorld@7c6768 is a string representation of the current object, and @7c6768 is a hashcode. In fact you are invoking toString() of current object

Here is java doc for toString() http://docs.oracle.com/javase/1.4.2/docs/api/java/lang/Object.html#toString()

edited Jul 26 '13 at 10:12

answered Jul 26 '13 at 10:07

ThiepLV

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score 3 · Answer 6 · answered Jul 26 '13 at 10:07

If you see the toString() method in Object class

/**
 * Returns a string representation of the object. In general, the
 * {@code toString} method returns a string that
 * "textually represents" this object. The result should
 * be a concise but informative representation that is easy for a
 * person to read.
 * It is recommended that all subclasses override this method.
 * <p>
 * The {@code toString} method for class {@code Object}
 * returns a string consisting of the name of the class of which the
 * object is an instance, the at-sign character `{@code @}', 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:
 * <blockquote>
 * <pre>
 * getClass().getName() + '@' + Integer.toHexString(hashCode())
 * </pre></blockquote>
 *
 * @return  a string representation of the object.
 */
public String toString() {
    return getClass().getName() + "@" + Integer.toHexString(hashCode());
}

It returns Class name followed by its hash code. That is the number you are getting.

score 2 · Answer 7 · answered Jul 26 '13 at 10:03

2

That is this.hashCode(). Since you do not redefine hashCode(), this number is the memory address in the JVM where the object is stored.

answered Jul 26 '13 at 10:03

tbodt

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score 2 · Answer 8 · answered Jul 26 '13 at 10:04

2

Look inside Objects' toString() method:

   public String toString() {
        return getClass().getName() + "@" + Integer.toHexString(hashCode());
   }

It is a hash value of the object.

answered Jul 26 '13 at 10:04

Alexey Odintsov

1,705
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Code Enthusiastic · Answer 9 · 2013-07-26T11:15:46.300

2

The number that identifies the object uniquely. It is Hexadecimal representation of hashcode. In simple terms, the whole String printed is the reference returned after instantiating the class.

edited Jul 26 '13 at 11:15

answered Jul 26 '13 at 10:05

Code Enthusiastic

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