Two marks Questions with Answers

Two Marks Questions with Answers

Q.1 Mention some of the separators used in Java programming.

Ans. : Some of the separators that are used in Java are as given below –

Q.2 How dynamic initialization of variables is achieved in java ?

Ans. The variables in Java are allowed to get initialized at run time. Such. type of initialization is called dynamic initialization.

For example

double a=5.0;

double b=20.0

double c=Math.sqrt((a+b));

Here the expression is evaluated at run time and its square root value is calculated and then the variable c is initialized dynamically.

Q.3 What is the output of the main method in the given code ?

public static void main(String[] args)

{

screen.write(sum());

}

static int sum()

{

int A=12;

int B=13;

return =A+B;

}

Ans. It will generate error at the statement return = A+B as "Illegal start of expression".

Q.4 What are the features of Java ?

1) Java is simple to implement.

2) Java is platform independent.

3) It is an object oriented programming language.

4) It is a robust programming language.

5) Java is designed for distributed system.

Q.5 Define objects and classes in Java.

Ans. An object is an instance of a class. The objects represent the real world entity. The objects are used to provide a practical basis for the real world. Each class is a collection of data and the functions that manipulate the data. The data components of class are called data fields and the function components of the class are called member functions or methods.

Q.6 Why are classes important in OO technology?

Ans. Classes bind together the relative data and methods in a cohesive unit. Due to this arrangement, only certain methods are allowed to access the corresponding data. Secondly, if any modification is needed, then the class can be viewed as one module and the changes made in one class does not spoil rest of the code. Moreover, finding error from such a source code becomes simple.

Hence use of class is very important thing in OO technology.

Q.7 What is the difference between object and class?

Following are some differences between the class and the object -

Q.8 What is the difference between structure and class?

Q.9 What is the difference between static and non static variables?

Ans. A static variable is shared among all instances of class, whereas a non static variable (also called as instance variable) is specific to a single instance of that class.

Q.10 Define encapsulation.

Ans. Encapsulation means binding of data and method together in a single entity called class.

Q.11 What is an abstract class?

Ans. When apply inheritance, the class becomes more and more specific as we move down. Sometimes a situation may occur that the superclass becomes more general and less specific. Such a class lists out only common features of other classes. Such a super class is called as abstract class.

Q.12 Define class. Give example.

Ans. Each class is a collection of data and the functions that manipulate the data. The data components of class are called data fields and the function components of the class are called member functions or methods.

For example

class Customer

{

int ID;

String Name; //Data Field

Customer() //Constructor

{ }

double withdraw_money() //method {...}

}

Q.13 What are the benefits of encapsulation? Should abstractions be user centric or developer- centric ?

Ans. Due to encapsulation the corresponding data and the methods get bound together by means of class. The data inside the class is accessible by the function in the same class. It is normally not accessible from outside component. Thus the unwanted access to the data can be protected.

The abstraction should be user centric. While developing the system using the O0 principles it is important to focus the user and not the developer.

Q.14 How would you declare an object of type animal named lion that takes a weight of 500 and length of 45 as parameters?

Ans.:

public class Animal

{

int weight, length;

Animal(int wt, int len)

{

weight=wt;

length=len;

}

void Show()

{

System.out.println("\n The weight of animal is: "+weight);

System.out.println("\n The length of animal is: "+length);

}

}

class AnimalMain

{

public static void main(String args[]).

{

Animal Lion=new Animal(500,45);

Lion.Show();

}

}

Output

The weight of animal is: 500

The length of animal is: 45

Q.15 What is meant by private access specifier?

Ans. The private access specifier allows classes, methods and data fields accessible only from within the own class. The functions outside the class cannot access the data members or the member functions.

Q.16 What do you mean by instance variable?

Ans. : An Object is an instance of a class. The variables that the object contains are called instance variables. For example consider a class Student

class Student

{

int RollNo;

char name[10];

}

Student S; //Creation of object of type Student class.

S= new Student();

If we create an object of the class Student say S, then using this object the variables RollNo and name can be accessed. These variables that belong to object S are then called as instance variables. Thus the Instance variables are any variables, without "static" field modifier, that are defined within the class body.

Q.17 Define constructor.

Ans. Constructor is a specialized method used for initializing the objects. The name of this method and the name of the class must be the same. The constructor is invoked whenever an object of its associated class is created.

Q.18 What is Static in Java ?

Ans. In java, static is a member of a class that is not associated with an instance of a class. If there is a need for a variable to be common to all the objects of a single java class, then the static keyword should be used in the variable declaration.

Q.19 What is the difference between a constructor and a method?

Ans. :

Q.20 What are key characteristics of objects?

 Ans. :

1.Object is an instance of a class.

2.Objects are runtime entities.

3. Using object of a class the member variable and member functions of a class can be accesses.

Q.21 What is meant by parameter passing constructors? Give example.

Ans. The constructor methods to which the parameter are passed are called parameter passing constructors

Example -

Rectangle(int h,int w)

{

height=h;

weight=w;

}

Q.22 Enumerate two situations in which static methods are used.

Ans. :

1) The situation in which object of belonging class is not created and we want to use the method of that class, then the method must be static.

2) For calling another static method, one such static method is used.

 3) For accessing static data the static method must be used.

 Q.23 List any four Java Doc comments.

Ans. :

Q.24 What is the need for javadoc multiline comments?

Ans. Javadoc multiline comments can be used to document all java source code. Comments follow a standard format consisting of a description followed by block tags. The first sentence of the description should be clear and concise as it is used in the summary of the API item.

Q.25 Define access specifier.

Ans. Access Specifier is used to set the accessibility of class members. There are three access specifiers in Java - (1) Public (2) Private (3) Protected.

Q.26 What is Javadoc ?

Ans. The Javadoc is a standard way to comment the java code. It has a special format of commenting the java code.

Q.27 Can Java source file be saved using a name other than the class name. Justify.

 Ans. Yes, we can save the java source file using a name other than the class name. But we should compile the program with file name and should run the program with the class name in which the main method exist. And there must not be any public class defined inside this java source file. For example, consider following Java code which is saved using the file name test.java

class A

{

public static void main(String args[])

{

System.out.println("Class A");

}

}

class B

{

public static void main(String args[])

{

System.out.println("Class B");

}

}

Output

Step 1: Compile the above program using following command

javac test.java

Step 2: Now execute the above program using

java A

The output will be

Class A

Step 3: If you execute the above code as

java B

The output will be

ClassB