Object Class

[Josweth Reddy]

Hai all,
As we know that java compliler will provide a default no-arg constructor,if we does not have any user defined constructor in our class.

How the object class constructor will be invoked and all the object class methods will be available to our class..??

Please claerify this doubt.

Thanks in advance,
Josweth Reddy

[Girish Nagaraj]

1)If we do not provide any constructor then default constructor will be added implicitly by the compiler to that class.
2)Now what I mean by default constructor is :
Your class: class A {}

This is what compiler generates for you:

class A extends java.lang.Object {
A() {
super(); // call to Object class constructor.
}
}

3)You can check this using javap JVM command.
class A {
}
>javac A.java
>javap A
class A extends java.lang.Object{
A();
}

4)If you extend some class other than java.lang.Object

Your code:class A {}
class B extends A {}

And this is what compiler generates for you:

class A extends java.lang.Object {
super(); // call constructor of Object class.Impilcit
}

class B extends A { // Now it doesn't extend Object class

super(); // call to superclass A constructor.
}

Let me know if thier is any mistake.

[Josweth Reddy]

Hai,
Thank you for the response.
But my doubt is ,How can we acces the Object class methods wothout creating an instance for the Object class.
For example:
we can apply equals() method without creating an instance for the Object Class.
How is it possible,to access the method of Object class without any instance???
Hope it is clear now.

Thanks in advance.
Josweth Reddy T.R
SCJP 1.4

[Amit Batra]

I think its because its[object class]is something that u get in the java.lang package which we all get by default and can use stuff like the System class or use any java keyword for that matter.

[wise owen]

Class Object is the root of the class hierarchy. Every class has Object as a superclass. All objects, including arrays, implement the methods of this class.

That is a IS-A relationship.