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) Explain repeated deletion of records.

A) //RepeatedDeletion.java import java.util.Scanner; import java.sql.*; class RepeatedDeletion {        public static void main(String[] args) {               Connection con= DriverManager. getConnection ( "jdbc:odbc:prince" , "scott" , "tiger" );               PreparedStatement ps=con.PreparedStatement( "DELETE FROM ACCOUNT WHERE ACCNO=?" );               Scanner s= new Scanner(System. in );               while ( true )               {                      System. out .println( "Enter accno : " );      ...
Post a Comment
Read more

Q) Retrieving data from database?

A)   ->to retrieve the data from database we need to submit SELECT statement from JDBC application. -> executeQuery() method of statement object is used for this purpose. This method has the fallowing ResultSet executeQuery(String sql) throws SQLException Ex: ResultSet rs = st.executeQuery(“SELECT * FROM ACCOUNT”); ->objectoriented representation of tables formate data is called ResultSet object. Ao the driver created one object i.e. ResultSet object. ->object orientation representation of a table of records returned from db is nothing but “ ResultSet ” object.  
Post a Comment
Read more

Q) What is the purpose of JDBC?

A) -> Java application can do any task by making a method (function) call. ->java method calls are not understandable to database management system. They can understand only SQL statements. ->SQL statements can’t be directly used in a java application. Java compiler complains. ->therefore, we say that java environment and database environment are heterogeneous to each other. Purpose of JDBC: ->for any kind of java application to communicate with any kind of database (management system) in a standard manner, JDBC is used.
Post a Comment
Read more