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Q) What is the output of the fallowing program ?



A)
// onjectexample.java
Class A
{
  Int  a;
Int b;
Void  x()
{
  System.out.println(a);
  System.out.println(b);
 }
}
Class objectexample
{
Public static void main(String a[])
{
A r;
r.x();
}
}

Answer :

The above program has syntactical error.
“ r” is a local , use define variable.
Without initializing “r” , it is used in method call.
Q)how to fix the above compilation error ?

Initialize “r” and then use it.
In java , a reference variable can have only 2 values.
1) null 04
2) object address (hash code)
In the above program if we initialize “r” to null , complication error is not raised by java compiler.
A.r=null;
r.x();
during program execution , “NullPointerException “ is raised.
User defined datatype variables are called reference in java.
The reference variable holds only 2 values, “null “or object address (# code)

When a reference is holding  “ null “ value o, if you call an instance method of a class by using that reference , “NullPointExcention“ is raised.
To avoid this exception we need to create object so that its address is stored in “r”.

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