Modifiers
|
What are access modifiers
|
These public, protected and private, these can be applied to class,
variables, constructors and methods. But if you don’t specify an
access modifier then it is considered as Friendly
|
Can protected or friendly features
be accessed from different packages
|
|
No when features are friendly or protected they can be accessed from
all the classes in that package but not from classes in another
package |
How can you access protected
features from another package
|
You can access protected features from other classes by subclassing
the that class in another package, but this cannot be done for
friendly features
|
What are the rules for overriding
|
Private method can be overridden by private, friendly, protected or
public methods
Friendly method can be overridden by friendly, protected or public
methods
Protected method can be overridden by protected or public methods
Public method can be overridden by public method
|
Explain modifier final
|
Final can be applied to classes, methods and variables and the
features cannot be changed. Final class cannot be subclassed,
methods cannot be overridden
|
Can you change the reference of the
final object
|
No the reference cannot be change, but the data in that object can
be changed
|
Can abstract modifier be applied to
a variable
|
No it is applied only to class and methods
|
Can abstract class be instantiated
|
No abstract class cannot be instantiated i.e you cannot create a new
object of this class
|
When does the compiler insist that
the class must be abstract
|
If one or more methods of the class are abstract.
If class inherits one or more abstract methods from the parent
abstract class and no implementation is provided for that method
If class implements an interface and provides no implementation for
those methods
|
How is abstract class different from
final class
|
Abstract class must be subclassed and final class cannot be
subclassed
|
Where can static modifiers be used
|
They can be applied to variables, methods and even a block of code,
static methods and variables are not associated with any instance of
class
|
When are the static variables loaded
into the memory
|
During the class load time
|
When are the non static variables
loaded into the memory
|
They are loaded just before the constructor is called
|
How can you reference static
variables
|
Via reference to any instance of the class
Computer comp = new Computer ();
comp.harddisk where hardisk is a static variable
comp.compute() where compute is a method
Via the class name
Computer.harddisk
Computer.compute()
|
Can static method use non static
features of there class
|
No they are not allowed to use non static features of the class,
they can only call static methods and can use static data
|
What is static initializer code
|
A class can have a block of initializer code that is simply
surrounded by curly braces and labeled as static e.g.
public class Demo{
static int =10;
static{
System.out.println(“Hello world’);
}
}
And this code is executed exactly once at the time of class load
|
|
Where is native modifier used |
It can refer only to methods and it indicates that the body of the
method is to be found else where and it is usually written in non
java language
|
What are transient variables
|
A transient variable is not stored as part of objects persistent
state and they cannot be final or static
|
What is synchronized modifier used
for
|
It is used to control access of critical code in multithreaded
programs
|
What are volatile variables
|
It indicates that these variables can be modified asynchronously
|