CODEWITHSUNDEEP
java
user3110007
user3110007

Reputation: 75

why non-static variable of another class is accessible in main class in java?

Here I am trying to access non-static variable 'a' of Test class in main. It is
accessible why? 

  class Test{  
      public static void m1(){}  
      public void m2(){}  
      public int a=20;  
      public static int b=30;  

     public static void fun(){  
       System.out.println(a);  //it gives an error because variable a is non-static  
       System.out.println(b);  
     }  
   }  

   class Test1{  

     public static void main(String args[]){  
       Test s=new Test();  
       s.b=10;  
       s.a=20;  
       System.out.println(s.a); /*why this statement not giving an error even variable'a'is  
       non-static, we are accessing it in static main() method */  
     }  
   }

Upvotes: 0

Views: 342

Answers (8)

Toon Borgers
Toon Borgers

Reputation: 3658

You're not getting any errors because you're accessing a member variable on an instance of Test. Example:

public class Foo{
  private static int bar;
  private int foobar;

  public static void main(String[] args){
      System.out.println(bar); // possible,because bar is static
      System.out.println(foobar); // illegal since you're trying to access an instance variable from a static context
      System.out.println(new Foo().foobar); // possible since you're accessing the foobar variable on an instance of Foo

Upvotes: 0

nestedloop
nestedloop

Reputation: 2646

I think you are mixing non-static and private.

All that is required to access a non-static public member is to hold an instance of the class.

If you don't want the member to be accessible, make it private/protected.

Upvotes: 0

JMM
JMM

Reputation: 4022

Variable a is accessible because it is public in your Test class, and you can access it from the static main method because you have created an instance of Test called s.

Upvotes: 1

user2357112
user2357112

Reputation: 280778

You can't use unqualified references to instance variables in a static method, because those implicitly refer to a this instance that doesn't exist. When you specify s.a, you are referring specifically to the a field of object s, rather than some non-existent this, so Java finds the field and lets you access it.

Upvotes: 1

Rahul
Rahul

Reputation: 45060

Non-static variables should be accessed using the class instance object and that is what you've done, which is why there is no error thrown by the compiler.

In fact, it is b which has been accessed wrongly(though it wont throw an error, but will show an warning saying static variables should be accessed in a static manner). Since it is static, you need to access it using the Class name.

Test.b = 20;

Also, you get the error in fun() method because you've tried to access a non-static field a inside a static context which is the fun() method. Even though main() is a static method, you've access a using an instance of Test class which is the right thing to do.

Upvotes: 0

Ivaylo Strandjev
Ivaylo Strandjev

Reputation: 70929

You are accessing the non-static variable via an instance(s) which is perfectly legal as the variable is public. Being static or non-static has nothing to do with access restrictions - the only thing that changes is if you need an instance to use it or not.

Upvotes: 0

MaGnetas
MaGnetas

Reputation: 5008

You're creating an instance of Test (s object) and accessing its public property. It's fine. It should work this way. The "static way" to access this property would be like this:

int x = Test.a;

And it will NOT work because your s attribute isn't static.

Upvotes: 0

SpringLearner
SpringLearner

Reputation: 13844

System.out.println(s.a); it will not give error because you are creating an object of test class and calling its variables

You might be confused about accessing static and non static variables in main method(static method for example).Consider this

you can directly write System.out.println(Test.b); but you can not write System.out.println(Test.a); as a is not static

Upvotes: 0

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