Question

JAVA basic quiz.

1. a) In order to run a java program, the computer must first compile the .java files to create .class files. Then the Java Virtual Machine (JVM) runs the .class files. After compilation, when the JVM first starts to run the program, what is created in memory first? When do instances of an object get created? How long do they stay in memory? Under what circumstances will the JVM delete an object from memory? b)What are the main components of a class in Java? What are the standard accessi- bility modifiers for each (e.g., protected, private, etc.)? When would you want to use a non-standard accessibility modifier for a variable? for a method? for a constructor?

Answer 1

1.a) i) The Java bytecode or Java classes are compiled to machine code and loaded into memory by the Java Virtual Machine for the first time.

a) ii)An instance is a specific realization of any object in OOP.The creation of instance is known as instantiation.An object varied in number of ways.Each realized variation of the object is instance.Each time when a program runs,it is an instance of program

Objects are created by constructor and it gets destroyed by destroyer.

Instantiation done by using new keyword.

Syntax:className objName=new className(input parameters)

a)III) when object is no longer in usage then garbage collector reclaims it's memory and reuse it for future memory allocation.Hence as long as object is in usage, they stay in memory.

a) iv)In java as soon as object has no longer any references,it becomes eligible for deletion.Once the object is no longer referenced and therefore it is not reachable by application code,the garbage collector removes and reuse the unused memory.

2.The class is defined as a blueprint or template that describes the behavior or state of an object.

It has main components like variable,method and constructor in java.

Syntax: <access specifier> class className{

// Class body

}

Accessibility Modifiers:

Java provides access through priavte,public and protected.

Private

It is specified with keyword private.It is accessible only within the class in which it is declared.Anyother class of same object will not be able to access.

Protected

It is specified with protected keyword.The method or datamember declared protected are accessible within same package or subclass in different package.

Public

It is specified with public keyword.It can be accessed from everywhere in the program i.e widest scope among all other access Modifiers.

Non-standard accessibility modifier:

• Java provide non access Modifiers to achieve many functionalities.
• The static modifier is for creating class methods and variables
• The final modifier is for finalizing the implementation of classes,methods and variables.
• The abstract modifier is for creating abstract classes and methods.
• Synchronized and volatile modifiers are used for thread concepts