Two marks Questions with Answers

Two Marks Questions with Answers

Q.1 Define the term inheritance.

Ans. Inheritance is a mechanism in which the derived class borrows the properties of the base class.

Q.2 Explain the use of extend keyword with suitable example.

Ans;

• The extend keyword is used in inheritance.

• When the child class is derived from its parent class then the keyword extends is used.

Q.3 What is the difference between superclass and subclass?

Ans. :

• The superclass is a parent class or base class from which another class can be derived.

•  The subclass is always a derived class which inherits the properties of the base class or superclass.

• The superclass is normally a generalized class whereas the subclass is normally for specific purpose.

Q.4 Enlist various forms of inheritance.

Ans. Various forms of inheritance are -

1. Single level inheritance

2. Multiple inheritance

3. Multi-level inheritance

4. Hierarchical inheritance

 5. Hybrid inheritance

Q.5 What is the use of super keyword ?

Ans. The super class is used to access immediate parent class from the subclass. It is used to

1. access parent's variable,

2. access parent's method

3. access patent's constructor invocation

Q.6 Differentiate between inheritance and polymorphism.

Ans. :

Q.7 Distinguish between static and dynamic binding.

Ans. Static binding is a type of binding in which the function call is resolved at compile time. The dynamic binding is a type of binding in which the function call is resolved at run time. The static binding is called the early binding and the dynamic binding is called late binding.

Q.8 What is the purpose of 'final' keyword ?

Ans. The keyword 'final' is used to avoid further modification of a variable, method or a class. For instance if a variable is declared as final then it can not be modified further, similarly, is a method is declared as final then the method overriding is avoided.

 Q.9 Define inheritance hierarchy.

Ans. The inheritance hierarchy represents the collection of classes the inherit from their base classes and thereby make use of the code present in the base class. The data reusability can be achieved by inheritance hierarchy. For example

Q.10 How to prevent inheritance?

Ans. If we declare particular class as final then no class can be derived from it. For example

final class Test

{

………..

………

……….

}

class Test1 extends Test

{

………..

………

……….

}

The above code will produce an error" cannot inherit from final Test".

Thus the use of keyword final for the class prevents the inheritance.

Q.11 Write a class declarations for the following relationship, assuming that all classes are public: a Bulldog is a kind of dog, and a Dog is a kind of Animal.

Ans;

class Animal

{

………….

}

class dog extends Animal

{

………...

}

class Bulldog extends dog

{

…………..

}

Q.12 What is meant by dynamic method dispatch?

Ans. The dynamic method dispatch is run time polymorphism in which a call to overridden function is resolved at runtime instead of at compile time. Hence is the name. For example

class Test1

{

public void method1()

{ }

}

class Test2 extends Test1

{

public void method1()

{ }

}

void main()

{

Test1 obj=new Test2();

obj.method1();

}

Q.13 Can an abstract class be final? Why?

Ans. The abstract class cannot be final because once we declared the abstract base class with the keyword final then it can not be inherited.

Q.14 Can an abstract class in Java be instantiated? Give the reason.

Ans. The abstract class can not be instatiated (i.e. we can not create the object of this class using new operator) because the abstract class is very much general and less specific. It does nothing and simply lists out only common features of other classes.

 Q.15 Why is multiple inheritance using classes a disadvantage in Java?

Ans. In multiple inheritance, the child class is derived from two or more parent classes. It can lead to ambiguity when two base classes implement a method with the same name. Q.16 State the condition for method overriding in Java

Ans. Method overriding occurs only when the name of the two methods(method in super class and method in subclass) are same and their type signature is same.

Q.17 What is package?

Ans.: Package represent a collection of classes, methods and interfaces. The name of the package must be written as the first statement in the Java source program. The syntax of specifying the package in the Java program is

package name_of_package

Due to package the systematic arrangement of classes is possible. All standard classes in Java are stored in named packages.

Q.18 Mention the necessity for import statement.

Ans. The import statement is used to refer the classes and methods that are present in particular package. This statement is written at the beginning of any Java program. For example -

import java.io.*

This statement allows to use the useful functionalities for performing input and output operations.

Q.19 List any four packages in java and highlight their features.

Ans. :

Q.20 What is API package?

Ans.: • The API packages are application programming interface packages used by java.

•  These packages include important classes and interfaces which are used by the programmer while developing the java applications.

• For example java.io, java.util, java.net and so on are the commonly used API.

Q.21 Explain any three uses of package.

Ans. :

1.The classes defined in the packages of other program can be easily reused.

2. Two classes from two different packages can have the same name. By using the package name the particular class can be referred.

3. Packages provide the complete separation between the two phases- design and coding.

 Q.22 Explain the term CLASSPATH.

Ans. The packages are nothing but the directories. For locating the specified package the java run time system makes use of current working directory as its starting point. This directory path is called CLASSPATH.

Q.23 What are the ways of importing the java packages? OR Write the syntax for importing packages in a Java source file and give an example.

Ans. The import statement can be written at the beginning of the Java program, using the keyword import. For example -

import java.io.File

or

import java.io.*

Either a class name can be specified explicitly or a * can be used which indicated that the Java compiler should import the entire package.

Q.24 In Java what is the use of interface?

OR  What is interface mention its use.

Ans. In java, the interface is used to specify the behaviour of a group of classes. Using interfaces the concept of multiple inheritance can be achieved.

Q.25 Define Interface and write the syntax of the Interface.

Ans. The interface can be defined using following syntax access_modifier interface name_of_interface

{

return_type method_name1(parameter1,parameter2,...parametern);

…………

return_type method_name1(parameter1,parameter2,...parametern);

type static final variable_name=value;

………...

}

The interface is a collection of various methods that can be used by the class that is attached to the interface. The interface name must be preceded by the keyword interface.

Q.26 What modifiers may be used with an interface declaration ?

Ans. : An interface may be declared as public or abstract.

Q.27 Why the variables in interface static and final ?

Ans. The members of interface are static and final because -

1) The reason for being static - The members of interface belong to interface only and not object.

2) The reason for being final - Any implementation can change value of fields if they are not defined as final. Then these members would become part of the implementation. An interface is pure specification without any implementation.

Q.28 What is the purpose of nested interface?

Ans. The nested interfaces are used to group related interfaces so that they can be easy to maintain. The nested interface must be referred by the outer interface or class. It can't be accessed directly.

Q.29 What are the properties of nested interface?

Ans;

1) Nested interfaces are static by default. You don't have to mark them static explicitly.

2) Nested interfaces declared inside class can take any access modifier.

3) Nested interface declared inside interface is public implicitly.

Q.30 If a class B is derived from class A and extends the interface myinterface, then how will you write this statement for class B definition?

class B extends class A implements myinterface

{

....//body of class B

}

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