CODEWITHSUNDEEP
javaclassmethods
dyso
dyso

Reputation: 37

Java - Why is it necesary to use Class class's instance methods write classname.class.method or instance.getClass().method?

Why is it necesary to use Class class's methods to write classname.class.method or instance.getClass().method?

For example:

public class SomeClass{
   public static void main (String[] args){
       SomeClass sm = new SomeClass();
       //The correct ways:
       System.out.println(sm.getClass().getName());
       //or
       System.out.println(SomeClass.class.getName()); 
   }
}

Class class's instance methods need a class (it can be seen when in System.out.println(sm.getClass().getName(); because sm.getClass() returns a class) so why is not correct to write System.out.println(SomeClass.getName(); and it is necessary to write "class" in the middle if getName() method is called by a class? Is it because SomeClass class is not considered an instance of Class class? Why sm.getClass() is considered an instance of Class class then?

Thank you.

Upvotes: 0

Views: 68

Answers (3)

shrikant
shrikant

Reputation: 441

I am breaking the line to understand the easy way.Hope so it will be helpful 

SomeClass sm = new SomeClass();

Class clazz1 = sm.getClass(); //sm.getClass() returns Class object
System.out.println(clazz1.getName());    

Class clazz2 = SomeClass.class; //SomeClass.class returns Class object 

System.out.println(clazz2.getName());

That means getName() method is available in Class class .

Upvotes: 0

davidxxx
davidxxx

Reputation: 131396

new SomeClass() creates an instance of the SomeClass class :

SomeClass someClass = new SomeClass();

It doesn't provide the Class instance of SomeClass as the getClass() instance method of Object class does :

Class<? extends SomeClass> clazz = new SomeClass().getClass();

These are two totally different things.

Upvotes: 4

Mike Nakis
Mike Nakis

Reputation: 62015

Why is it necesary to use Class class's methods to write classname.class.method or instance.getClass().method?

Java has no free-standing functions, so in order to invoke any function, you have to invoke it as a member of a class. And if you want to invoke a function that belongs to class A, you have to invoke it as a method of class A. I know this is a tautology; but this is what your question, as stated, calls for.

why is not correct to write System.out.println(SomeClass().getName();

It is not correct to write that, because it is not valid java syntax. Java reserves the class-name-followed-by-parentheses construct to stand for identifying constructors. (And it must be prefixed by new.)

it is necessary to write "class" in the middle if getName() method is called by a class?

Besides not supporting free-standing functions, java does not support any free-standing code whatsoever, so in order to call anything, the calling code must be in a class, so all methods are called by a class.

Is it because SomeClass class is not considered an instance of Class class?

Uhm, yes.

Why sm.getClass() is considered an instance of Class class then?

It is not considered an instance of a class. But it does return an instance of a class.

Upvotes: 1

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