OOPJ_GTU_Dec-2010

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GTU Exam Paper Solution: By Paresh Bhavsar

Paresh Bhavsar (www.j2eetrainer.com) Page 1

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Q . 1 (a) Differentiate between constructor and method of class. Define

method overloading and its purpose. Write a program to demonstrate

constructor overloading.

Methods are functional units of the class. Each method signature includes -

1. name (e.g. add)

2. return type (e.g. void

3. parameters (e.g. int x, int y)

Below mentioned are some of the examples of the methods.

1. int test (int x, int y) { < }

2.

void run (double speed) { < }

There are three characteristics of constructor. (diff between constructor and

method)

1. Constructor does not have return type.

2. Constructor does not have name MUST be same as class name.

3. Constructors are called only at the time of the object creation.

Below mentioned is constructor example

class Student {

int rollno;

Student(int rollno){

this.rollno = rollno;

}

}

Method overloading supports static polymorphism. Overloaded methods

are defined in the same class. Overloaded methods have same method

name but different no. of parameters or type of parameters. For example

below mentioned are overloaded methods.

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class X1 {

void test(){

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Q. 1 (b)

Write a program to create directories (/home/abc/bcd/def/ghi/jkl) in the

home directory /home/abc and list the files and directories showingfile/directory, file size. Read-write-execute permissions. Write destructor

to destroy the data of a class.

import java.io.File;

public class MyFileDemo {

public static void main(String[] args) throws Exception {

File f = new File("/home/abc", "bcd");

// if windows OS change to d:/home/abc (home and abc should //

be already created in the d:/

f = new File(f,"def");

createNewDir(f);

f = new File(f,"ghi");

createNewDir(f);

f = new File(f,"jlk");

createNewDir(f);

f = new File("/"); // if windows OS change / to d:/

String[] list = f.list();for(String s : list){

f = new File(f, s);

System.out.println(f.getAbsolutePath());

}

}

public static void createNewDir(File f) {

if(!f.exists()) {

f.mkdir();}

}

}

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Q. 2 (a)

Define polymorphism with its need? Define and explain static and

dynamic binding using program?

Poly means many. When we have one behavior which is implemented in

many ways we can achieve polymorphism. For example below, we have

two constructor of the Student class. Default constructor and

parameterized constructor. This is called constructor overloading. We can

also have method overloading, in below example we have setValues

method with two arguments and another method with one argument only.

class Student {

private int id; // id and name cannot be accessed outside the class

private String name;

public void setValues(int rollno, String name) {


this.name = name;

}public void setValues(int rollno) { // method overloading


}

public Student() {

}

public Student(int rollno, String name) { // constructor overloading


this.name = name;}

}

It is clear from above example that names of the method remains the same

which is setValues. There is change in no. of parameters. Now when

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Student class object needs to call setValues method it can call setValues

method with one Parameter or with two parameters.

We have seen that static polymorphism is achieved using method

overloading. To understand dynamic polymorphism lets first understand

method overriding concept. Method overriding is achieved by keeping

method signature same. Method signature includes return type, name of

the method and arguments. For example, if we have printStudent method

to be overridden we will write the printStudent method with the same

signature in the sub-class. Below mentioned example explain the same

concept.

class Student {

int id;

String name;

public void printStudent() {

System.out.println(I am student);

}

}

class EnggStudent extends Student {

public void printStudent() { // overridden method

System.out.println(I am Engineering student);

}

}

class ScienceStudent extends Student {

public void printStudent() { // overridden method

System.out.println(I am Science student);}

}

class StudentDemo {

public static void main(String args[]){

Student s1 = new Student();

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s1.printStudent();

EnggStudent s2 = new EnggStudent();

s2.printStudent();

ScienceStudent s3 = new ScienceStudent();

S3.printStudent();

}

}

As we can see in mentioned example, printStudent method is overridden

in sub-class. The implementation of the method is different. Now, if we

create the student class object and call the printStudent method, we will

have o/p printed on the console screen will be I am Student. We can

create object of the EnggStudent and call printStudent method, o/p will be

I am Engineering Student.

Ideally we should have created reference of the Student Class which is

pointing to the object of Student class, EnggStudent and ScienceStudent.

class StudentDemo {


Student s1 = new Student();

s1.printStudent();

s1 = new EnggStudent(); // same reference (s1) pointing to// EnggStudent now

s1.printStudent();

s1 = new ScienceStudent(); // same reference(s1) pointing to

// CommerceStudent now

s1.printStudent();

}

}

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Q. 2 (a) Explain single and multiple inheritances in java. Write a program

to demonstrate combination of both types of inheritance as shown in

figure 1. i.e.hybrid inheritance

Single inheritance is when one java class extends another Java class or

implements one interface. For example,

class C1 extends C2 {

increment(p.x); is pass by value in which p.x value is

copied into another variable x (x is local variable in the increment method).

Changing the value of the x does not affect the original value (p.x).

When we call the increment method and passing p as a reference, p1

reference also points to the same object where p is pointing. So any change

in the p1 (p1.x++) will affect the value of p (p.x will be incremented also).

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Q. 3 (a)

Define generics in Java. Write a program to demonstrate generic class

and constructor.Generics is facility added in java programming in 2004 as a part of J2SE 1.5

This allows type or method to operate on objects of various types while

providing compile time safety. Common use of generics is when using Java

Collection that can hold objects of any type, to specify the type of objects

store in it.

Below mentioned is a simple program to create generics.

class MyGenericClass {

private T t;

public MyGenericClass(T t){

this.t = t;

}

}

class MyGenericDemo {

public static void main(String[] args) {Car c1 = new Car();

MyGenericClassgenClass = new MyGenericClass(c1); }

}

Whenever we create any List /Map or Set we use generics to store specific

objects to the Collection for example,

List list = new ArrayList();

Generics ensures that now, we can add only string objects to thelist. If we

try to add any objects other than string it shows compilation error. So using

Generics compile time check of the objects type is possible and no

ClassCastException will be generated.

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Q. 3 (b)

Differentiate between abstract class and interface specifying matrices of

differences. Write a program to define abstract class, with two methodsaddition() and subtraction(). addition() is abstract method. Implement

the abstract method and call that method using a program(s).

abstract Class Interface

Abstract class has atleast one

abstract method

Interface has all abstract method

By default methods are NOT

abstract and public in abstract class

By default all methods are abstract

and public in interface

abstract classes are extended by

other class using extends keyword.

Interfaces are implemented by other

class using implements keyword

One class can not extends two or

more abstract classes

One class can implements two or

more interfaces

Variables defined in the abstract are

NOT static and final by default

Variables defined in the interfaces

are static and final by default

abstract class MyClass {

abstract int addition(int x, int y);

int substraction(int x, int y) {

return x - y;

}

}

class MyClassImpl extends MyClass {

int addition(int x, int y) {

return x + y;

}

}

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class MyClassImplDemo {

public static void main(String[] args) {

MyClassImpl cls = new MyClassImpl();

int result = cls.addition(10, 20);

System.out.println("Result is " + result);

}

}

Q. 4 (a)

Write an event handling program to handle feedback form of GTU

examination system using your creativity.

public class prjFeedbackForm {

public static void main(String [ ] args) {

Frame frame = new Frame("GTU Feedback Form");

Panel p = new Panel(new GridLayout(6, 2,0,20));

Label lName = new Label("Enter Name :");

final TextField tfName = new TextField(10);

Label lCourse = new Label("Course Name");

final TextField tfCourse = new TextField(10);Label lCollegeName = new Label("CollegeName");

final TextField tfCollege = new TextField(10);

Label lComment = new Label("Enter Comment");

final TextField tfComments = new TextField(10);

CheckboxGroup group = new CheckboxGroup();

final Checkbox cb1 = new Checkbox("Good",group,true);

final Checkbox cb2 = new Checkbox("Excellent",group,true);

Button b = new Button("Send");b.addActionListener(new ActionListener() {

@Override

public void actionPerformed(ActionEvent e) {

String name = tfName.getText();

String course = tfCourse.getText();

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String comments = tfComments.getText();

String college = tfCollege.getText();

System.out.println("Name of the Student " + name);

System.out.println("Course of the Student " + course);

System.out.println("Comments from the Students " +

comments);

System.out.println("College Name " + college);

}

});

p.add(lName);

p.add(tfName);

p.add(lCourse);

p.add(tfCourse);

p.add(lCollegeName);

p.add(tfCollege);

p.add(lComment);

p.add(tfComments);

p.add(cb1);

p.add(cb2);

p.add(b);frame.add(p);

frame.setLocation(200, 200);

frame.setSize(200, 240);

frame.setVisible(true);

}

}

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Q. 4 (b)

Write a program to replace all word1 by word2 from a file1, and

output is written to file2 file and display the no. of replacement.

class command {


System.out.println(args[0]);

File f = new File(args[0]);

if (f.exists()) {

System.out.println("file exist");} else {

System.out.println("File does not exist");

return;

}

try {

FileReader fr = new FileReader(f);

StringBuffer str = new StringBuffer();

int i = fr.read();while (i != -1) {

str.append((char) i);

i = fr.read();

}

System.out.println(str);

String content = str.toString();

StringTokenizer tokenizer = new StringTokenizer(content,

"word1");System.out.println(tokenizer.countTokens());

content = content.replaceAll("word1", "word2");

System.out.println(content);

int counter = 0;

int index = content.indexOf("word2");

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while(index!=-1){

counter++;

index = content.indexOf("word2",index+"word2".length());

}

System.out.println(counter);

FileOutputStream fos = new FileOutputStream(args[0]);

fos.write(content.getBytes());

fos.close();

} catch (Exception e) {

e.printStackTrace();

}

}

}

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Q. 4 (a)

Write an event handling program to handle e-mail sending form using

your creativity.

import java.awt.Button;

import java.awt.*;

import java.awt.event.*;

public class EmailSendDemo extends Frame {

public EmailSendDemo(String frameName) {

super(frameName);

}


EmailSendDemo frame = new EmailSendDemo("Email Send Form");

Panel panel = new Panel();

Label lSend = new Label("To ");

Label lcc = new Label("cc ");

Label lbcc = new Label("bcc ");

final TextField tfSend = new TextField(10);

final TextField tfcc = new TextField(10);

final TextField tfbcc = new TextField(10);

final TextField tfsubject = new TextField(10);

final TextArea taContent = new TextArea(10,15);

Button bSend = new Button("send");

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bSend.addActionListener(new ActionListener() {

@Override

public void actionPerformed(ActionEvent e) {

String toEmailAddress = tfSend.getText();

String ccEmailAddress = tfcc.getText();

String bccEmailAddress = tfbcc.getText();

String msg = tfsubject.getText();

String content = taContent.getText();

System.out.println("Sending Email ...");

}

});

panel.add(lSend);

panel.add(tfSend);

panel.add(lcc);

panel.add(tfcc);

panel.add(lbcc);

panel.add(tfbcc);

panel.add(taContent);

panel.add(bSend);

frame.add(panel);

frame.setSize(150,350);

frame.setVisible(true);

}

}

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Q. 5 (a)

Explain the importance of Exception handling in java. Write a program to

handle NoSuchMethodException, ArrayIndexOutofBoundsException

using try-catch-finally and throw.

Below mentioned are some of the benefits of exception handling.

1. Program does not abruptly stops. Program continues excecution as if

nothing has happened.

2. Exceptions are unwanted situation, which programmer wants to

handle. Using try block as guarged block and catch block exceptionare handled.

3. finally block is helpful in relasing the resources because it is always

executed.

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public class ExcTest {


try {

testNoSuchMethodExcetpion(); // NoSuchMethodException is

// checked. Method must be called from try block only.

} catch (NoSuchMethodException ex) {

ex.printStackTrace();

}

pop(11); // no need to call from try-catch as

// ArrayIndexOutofBounds is unchecked exception

}

static void testNoSuchMethodExcetpion() throws

NoSuchMethodException {

throw new NoSuchMethodException("Exception NoSuchMethod.");

}

static int[] x = new int[10];

static int pop(int position) {if(position>=0)

throw new ArrayIndexOutOfBoundsException("Arrays max size :

10");

else

return x[position];

}

}

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Q. 5 (a)

Explain the importance of Exception handling in java. Write a program to

handle NoSuchMethodException, ArrayIndexOutofBoundsExceptionusing try-catch-finally and throw.

Difference between error and exception

1. All exception as sub-classes of exception class while all errors are

sub-classes of Error class

2.

Error cannot be handled programmatically.3. Exception can be handled using try-catch block by java programs.

4. OutofMemoryError is an example of Error while Exception examples

are ArithmaticException, IOException etc.

public class ExcTest {


try {

testInterruptedExcetpion(); // NoSuchMethodException is

// checked. Method must be called from try block only.

} catch (NoSuchMethodException ex) {

ex.printStackTrace();

}

test();

}

static void testInterruptedExcetpion () throws InterruptedExcetpion {

throw new InterruptedExcetpion("Exception InterruptedException.");

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}

static int test(int rollno) {

if(rollno

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t1.start();

URLDemo retrieve = new URLDemo();

retrieve.isAdd = false;

Thread t2 = new Thread(retrieve);

t2.setName("RETRIEVE Thread : ");

t2.start();

Thread t3 = new Thread(retrieve);

t3.setName("RETRIEVE Thread : ");

t3.start();

}

public void rruunn() {

try {

int x = 0;

while (true) {

if (isAdd) {

x++;

data.put("key" + x, "URL : " + x);

Thread.sleep(1000); // to see better output...System.out.println("Key Successfully added. " + data);

} else {

String key = "key" + (int)(Math.random()*100);

String url = data.get(key);

// genereted some random key and searching for

if (url != null) {

System.out.println("URL for key is " + url);

} else {System.out.println("No key found : " + key);

}

Thread.sleep(1000); // to see better output...

}

}

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} catch (Exception e) {

e.printStackTrace();

}

}

}

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