Skip to main content

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”.

Comments

Post a Comment

Popular posts from this blog

Q) What is JDBC driver? What is its role in java database connection?

A) ->A translation software written in java according o JDBC specification is nothing but “JDBC driver”. -> JDBC driver implements JDBC API. Use single API. JDBC driver role: They are 4 roles   1)       Establishing connection between JDBC client and database server. 2)       Receiving JDBC method calls made by JDBC client while performing database (CRUD) operations. 3)       Translating java method calls into DBMS understandable calls and forwarding them to database server. 4)       Receiving the results from database server. Translating them into java format and handling over the same to the JDBC client.
Post a Comment
Read more

Q) What is ODBC?

A) ->open database connectivity is a technology from MS that enables any language program (other than java) to communication with database Management System. ->in java program ODBC is directly not allowed for the fallowing reasons 1) OS dependency 2) Procedural oriented approach 3) Security thread
Post a Comment
Read more

Q) Explain about nested classes?

A) ->defining a class with in another class is known as nesting of the class. Ex: class A {        class B        {                      } //nested class, and inner class.because it is not static class. } //enclosing class or outer class. ->static class is declared in inside an another class then it does not become an inner class. Note: non-static nested class is known as “inner class”. In the above example class B is nested but not an inner class. Ex: class D {        static c        {                      } //nested class, but not an inner class , because of static class. } //outer class. ->we have three different kinds of inner classes. 1) Member inner class 2) Meth...
Post a Comment
Read more