|
| | 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
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