Chapter 3,4,5,6,7,8

                                     

 Some Important Questions with Answers (Java, Netbeans)

                                        Chapter 3,4,5,6,7,8

1.    Which window is used to designed the form.
Ans:   Design window

2. Which window contains the Swing Controls components. Ans:   Palette window

3. What is the most suitable component to accept multiline text. Ans : Text Area

4. What will be the output of the following command? Learning.concat("Java")

Ans : Error

5. What will be the output of the following command? "Learning".concat("Java")

Ans:   LearningJava

6. Name the different list type controls offered by Java Swing. Ans: (i) jListBox

(ii) jComboBox

7. Name any two commonly used method of ListBox.
Ans: getSelectedIndex() and getSelectedValue()

8. Write code to add an element (“New Course”) to a list (SubList) at the beginning of the list. Ans: SubList.add(0,”New Course”);

9. Describe the three common controls. Also give some of their properties.
Ans:

(i)          jButton       text,icon

(ii)         jLabel         text,border

(iii)        jTextField   text,font

10. By default a combo box does not offer editing feature.How would you make a combo box editable. Ans: By setting its editable property to false.

11. Write Name the component classes of Swing API for the following components-

(a)    frame (b)   button

Ans:(a)JFrame(b)JButton

12.   What is the name of event listener interface for action events ? Ans: ActionPerformed

13. What does getpassword() on a password field return ? Ans: a character array

14. What is event driven programming?

Ans:This programming style responds to the user events and is driven by the occurrence of user events.

15. What are containers? Give examples.

Ans: Containers are those controls inside them e.g., frame (JFrame), Panel (JPanel), label (JLabel) etc. are containers.

16. Which method of list is used to determine the value of selected item, if only one it Ans: getSelectedValue()

17. Which type of storage is provided by variables.
Ans: temporary

18. What will be the output of the following code segment:
      String firstName = "Johua ";

String lastName = "Yacomo";

String fullName = firstName + lastName;
      jTextField1.setText("Full Name: ");
      jTextField2.setText (fullName);
 Ans:   Full Name:

JohuaYacomo

19. Which expression is used to print the value of a variable "x" of type int. Ans:   jTextField1.setText("x = " + x);

20. The statement i++; is equivalent to
Ans :i=i+1

21. Name the primitives datatypes in java.

Ans: Numeric type , Fractional type, Character type and Boolean type.

22. Which events gets fired when a user click a JButton and JRadioButton. Ans: ActionPerformed

23. Which of the following is a selection construct ?

a.   do while Loop b. for Loop c. while Loop d. None of these Ans:   none of these

24. What will be used if there are two or more possible options. Ans:   is else if and switch

25. Name the loop that never ends.
Ans: infinite loop

26. Which braces is used to enclose statements in a block statement. Ans:   { } Curly braces

27. Which of the following is an exit controlled loop?

a. for loop b. do while Loop

c. while loop d. none of these
Ans: do while loop

28.Which process is used to translate a task into a series of commands that a computer will use to perform that task.

Ans: Project design

29. Which of the following component is the best suited to accept the country of the
user?

A. List

B. Combo box

C. Radio button

D. Check box

Ans: List and combo box

30. Which construct will be used to find the sum of the first 10 natural numbers? Ans: for loop

31. Which of the following is not a good programming guideline? Ans : Using text fields to accept input of marital status

Short answers type questions:

1. Explain the following terms:

a) IDE

b) Form
Ans:

a) IDE : IDE is an acronym for Integrated Development Environment which is a work environment that integrates all tools necessary for Application Development
and makes them available as part of one environment.

b) Forms: Forms are used to accept data (input) and submit data to an external agent for processing.

2. Explain the usage of the following methods :

a) setText()

b) toString()

c) concat()
Ans:

a) setText() : It is used to change the display text of a component (label, text field or button) during run time.

b) toString() :   It is used to convert an Integer value to String type.

c) concat() : The concat() method or the string concatenation symbol(+) may be used to add two strings together.

3. Differentiate between:

Ans:

a) Text field and Text area components :

The Text Field allows the user to enter a single line of text only. But Text Area component allows   to accept multiline input from the user or display multiple lines of information.

b) Text field and Password field components:

The Text Field displays the obtained text in unencrypted form whreas password field displays the obtained text in encrypted form. This component allows confidential input like passwords which are single line.

c) parseInt() and parseDouble() methods:

parseInt() is used to convert a string value to Integer type whereas parseDouble() is used to convert a string value to type Double.

4. What is a Variable?

Ans: Variables are named temporary storage locations.

5. Why are data types important?

Ans: Data Types define the way the values are stored, the range of the values and the operations that can be performed on that type.

6. How are keywords different from variable names?

Ans: Keywords have special meaning in java, should not be used as the variable names. Variables are named temporary storage locations.

7. What is an identifier?

Ans:Identifiers are fundamental building block of a program and are used as the general terminology for the names given to different parts of the program viz. variables, objects, classes,functions, arrays etc.

8. What is casting? When do we need it?

Ans:Casting is a conversion, which uses the cast operator to specify the type name in parenthesis and is placed in front of the value to be converted.

For example: Result = (float) total / count ;

They are helpful in situations where we temporarily need to treat a value as another type.

9. What is the purpose of break statement in a loop?

Ans:In a loop, the break statement terminates the loop when it gets executed.

10. Is Java case sensitive? What is meant by case sensitive?

Ans: Yes java is case sensitive. Case sensitive means upper case letters and lower case letters are treated differently.

11. Is a string containing a single character same as a char?

Ans: No

12. What is the main difference between a combo box and a list box?

Ans: The List Box does not have a text field the user can use to edit the selected item, wheras a Combo Box is cross between a text field and a list.

13. Explain the use of for statement along with its syntax.

Ans: The for loop repeat a set of statements till a test condition is satisfied. The syntax of the for loop is:

Syntax

for( initialization; test exp; increment/decrement exp)
{

statements;
}

14. What is the difference between selection and repetition?

Ans: Selection statements test conditions and selectively execute code depending on the outcome of the
test condition , whereas repetition statements repeat a set of statements till a test condition is satisfied.

15. What is the purpose of if statement? Name the different forms of if statement.

Ans: The if statement allows selection (decision making) depending upon the outcome of a condition.

a)   simple if

b)   if else

c)   if -   else if - else

16. What is the purpose of default clause in a switch statement?

Ans: The default statement gets executed when no match is found in switch.

17. What is the main difference between a while loop and a do while loop?

Ans: In while loop test expression is evaluated at the beginning of the loop whereas in do while loop the test
expression is evaluated at the bottom of the loop. This means that do-while loop is executed at least once.

18. How is the if…else if combination more general than a switch statement?

Ans:The  switch  statement  must  be  by  a  single  integer  control  variable,  and  each  case  section  must correspond  to  a  single  constant  value  for  the  variable.  The  if…else  if  combination  allows  any kind  of condition after each if.

19. Excessive comments add time to the execution of your program. (True/False).

Ans: False because comments are non executable.

20. Differentiate between compile time and run time errors.

Ans:  Compile  time  errors  refer  to  the  errors  that  violate  the  grammatical  rules  and  regulations  of programming language.

21. Which error is harder to locate and why?

Ans: Logical errors because in presence of logical error , the program executes without any problems but the output produced is not correct. Therefore every statement of the program need to be scanned.

22. Explain the following terms:

a)  Exception  handling  :  Run  time  errors  are  also  called  exceptions,  and  handling  such  errors  in  the application is called exception handling.

b) Syntax : Formal set of rules defined for writing any statement in a language is known as syntax.

c) Portability : The application should be portable. It should be able to run on different platforms.

d)  Prettyprinting   :  Prettyprinting  is  the  formatting  of  a  program  to  make  it  more  readable.  These

formatting conventions usually consist of changes in positioning, spacing, color, contrast, size and similar modifications intended to make the content easier to view, read and understand.

e) Syntax error: Syntax errors occur when syntax rules of any programming language are violated. These errors occur during compilation of the application

OutPut   Finding Questions:

1 Write the output :

(i) System.out.printl(“Hello”.charAt(3));

(ii) System.out.printl(“Good morning”.substring(4));
Ans:

(i)         l

(ii)   morning

2. Write the output of the following code :

intx , y = 0;

for(x=1;x<=5;++x)
y = x++;

--y ;

Ans: 7   4

3. Find the output of the code:

int f=1,i=2;

do

{   f*=i;

}while(++i<5);

System.out.println(f);

Ans: 24

4. What would the following code do :

Connection , statement created

String str=”select * from emp”;

Resultsetrs= stmt.executeQuery(str);
rs.last();

int r= rs.getRow();

JOptionPane.showMessageDialog(null,””+r);

Ans : if emp table has 5 records it will display 5

5.   What will be the output of the following code segment:

String firstName = "Johua ";

String lastName = "Yacomo";

String fullName = firstName + lastName;
jTextField1.setText("Full Name: ");
jTextField2.setText (fullName);

Ans: Full Name :

JohuaYacomo

6. What will be the value of j and k after execution of the following code:

int j=10,k=12;

if(k>=j)

{k=j;

J=k;
}

Ans: 10    10

7.   How many times, the following loop gets executed?

i=0;

while (i> 20)
{

//Statements
            }

Ans: 0 times

8. How many times, the following loop gets executed?

i=0;

do

{

//Statements
}while (i> 20);

Ans: 1 time

9. What will be the contents of jTextield1 and jTextField2 after executing the following statement:

StringBuffer s= new StringBuffer(“Common Wealth”);

Int c=s.capacity();

s.insert(0,’E’);

s.reverse();

jTextField1.setText(“”+c);

jTextField2.setText(s.toString());
Ans:

29

htlaeWnommoCE

10. What will be the contents of jTextield after executing the following statement:

int num=4;

num=num+1;
if(num>5)

jTextField1.setText(Integer.toString(num));

else

jTextField1.setText(Integer.toString(num*4));

Ans : 7

11. Find the output of the following code:

int First = 7;

int Second = 73;
First++;

if (First+Second> 90)

jlabel1.setText("value is 90 ");
else

jlabel1.setText("value is not 90 ");
Ans :value is not 90

12. Find the output

int Number1 = 7,Number2=8;
int Second = 73;

if (Number1>0 || Number2>5)
if (Number1>7)

jTextField1.setText("Code Worked");
else

jTextField1.setText("Code MightWork");
else

jTextField1.setText("Code will not Work");
Ans :Code MightWork

13. How many times will the following loop get executed?

x = 5;

y = 36;

while ( x <= y)
{

x+=6;
}

Ans: 6

14. What will be the content of the jTextArea1 after executing the following code? Int Num = 1;

do

{

jTextArea1.setText(Integer.toString(++Num) + "\n");
Num = Num + 1;

}while(Num<=10)
Ans: 10

15. What will be the contents of jTextfield1 and jTextfield2 after executing the following code:

String   s=”KENDRIYA VIDYALAYA GUNA” jtextfield1.setText(s.length()+” “);

jtextfield2.setText(Math.round(2.34)+“”);

Ans   : 23  2

16. What will be the value of s after executing the following code?

double   i,sum=2

for(i=3;i<8;++i)

{      if(i%4= =0)

{     break;

sum=Math.pow(sum,i);
                 }

else

sum+=i/2;
            }

Ans: 150.0625

17. What will be the content of jTextField1 and jTextField2 after executing the following code:

String st=”New to Information Technology”;

jTextField1.setText(st.replace(“Technology”,”Practices”); jTextField2.setText(st.substring(7));

Ans: New to Information Practices

Information Technology

18. Predict the output for tan & tan1 if sac equals 7?

int tan = 0, tan1 = 4 ;
if ( sac == 2 )

{   tan = 4 ; tan1 = 0;    }

else if (sac == 8)

{ tan = 0 ; tan1 = 4; }

JOptionPane.showMessageDialog( null , “ tan = “ + tan +” , tan1 = “ + tan1 ) ;

Ans: tan = 0          tan1=4

19. Give the output for the following code fragment:

v = 20 ;
do

{

JOptionPane.showMessageDialog( null , v + “   ” ) ; } while ( v< 50 ) ;

JOptionPane.showMessageDialog( null , “ Bye “ ) ;

Ans: Infinite loop

20. Give the value of x after executing following Java code. Also find how many times the following loop will execute? :

int a=10;

int b=12;
int x=5;
int y=6;

while   (a<=b)

{      if (a%2= =0)
             x=x + y;

else

x=x-y;

a=a+1;

}

Ans:11

21. What will be the output produced by following code fragment? (1)

flaot x=9;

float y=5;

int z=(int)(x/y);
switch(z)

{

case1:x=x+2;
case2: x=x+3;
default:x =x+1;
}

System.out.println(“value of x:”+x);

Ans: 15

22.   Predict the output of the following code fragments:

inti,j,n;

n=0;i=1;
do

{ n++; i++;
}

while(i<=5);
Ans: 5

23. What will be the output of the following program code when the user will press JButton:

Public class svm

{           int a;

svm(int p)

{           a=p;                 }

void assign(int no)

{           a=no;                }

intdisp()

{           return a;            }

}

private void jButton1ActionPerformed(java.awt.event.ActionEventevt)
{

svm os=new svm(15);

System.out.println(“         “ + os.disp());

os.assign(35);

System.out.println(“         “ + os.disp());

}

Ans: 15           35

24. What will be the contents of jTextField1 and jTextField2 after executing the following code:

String s = “Sun Micro Systems”;

jTextField1.setText(s.length()+””);

jTextField2.setText(s.toLowerCase());
Ans:

jTextField1 : 17

jTextField2 : abc micro systems

25. What values will be assigned to the variable ua ,ub, uc and fail after execution of the   following program segment:

int i=0,ua=0,ub=0,uc=0,fail=0;
while(i<=5) {

switch ( i++ )

{           case   1 :++ua;

case   2 : ++ub; uc++;break;
case   3 :

case   4 : ++uc; ua++;ub++;break;
default : ++fail;

}

Ans: ua=1   ub=1   uc=0

26. Predict an output of the following code fragments:

int i = 1,      j = 0,    n = 0;
while(i<4) {

for(j=1;j<= i ; j++)

{           n+= 1;

i = i+1;

}

System.out.println(n);
}

Ans : 6

27. Give the output of the following code:

int m=100;

while(m>0)
{

if (m<10)
break;

m=m-10;
}

System.out.println(“m is “+m);

Ans: 0

Errors finding questions:

1.   The following code has some errors. Rewrite the corrected code .

int i=2,j=5;

while j>i

{    jTextField1.getText(“j is greater”);
j--; ++i;

}JOptionPane.showMessageDialog(“Hello”);
Ans:

int i=2,j=5;
while( j>i)

{    jTextField1.getText(“j is greater”);
j--; ++i;

}JOptionPane.showMessageDialog(“Hello”);

2.   Identify the errors :

switch(ch)

{           case ‘a’   :

            case ‘A’ :            case ‘e’ :             case ‘E’ :            case ‘i’ :            case ‘I’ :             case ‘u’ :

case ‘U’ : ++vowels;
            break;

default : ++others;

Ans: two case constants doesn’t have the same value

3.   inti,j=5;

i==j+5;
if(i=j)

{

jTextField1.setText(“i and j are unequal”);

jTextField2.setText(“they are not equal”); break;
    }

else jTextField1.setText(“i and j are equal”);
Ans:

int i,j=5;
i=j+5;

if(i==j)
{

jTextField1.setText(“i and j are unequal”);

jTextField2.setText(“they are not equal”); break;
    }

else jTextField1.setText(“i and j are equal”);

4.   Rewrite the code after making correction . Underline the corrections
      int sum;value;inct;

int i

for(i==0;i<=10;i++)
sum=sum+i;

inct++;

Ans :

int sum,value,inct;
int i;

for(i=0;i<=10;i++)
sum=sum+i;

inct++;

5. The following code has some error(s). Rewrite the correct code underlining all the corrections made.

int y=3;

switch(y);

{   case 1: System.out.print(“Yes its One”);

case>2: System.out.println(“Yes its more than Two”); break;

case else: System.out.print(“Invalid Number):

ans:

int y=3;
switch(y)

{   case 1: System.out.print(“Yes its One”);

break;

case 2: System.out.println(“Yes its more than Two”); break;

default:System.out.print(“Invalid Number):

}

6.   The following has some error(s).Rewrite the correct code underlining all the corrections made:

Inti,j=5;

i==j+5;
if(i=j)

{

jtextfield1.setText(“I and j are unequal”);

jtextfield1.setText(“I and j are not equal”);breaks;
}

else

jtextfield1.setText(“I and j are equal”)

Ans:

inti,j=5;
i=j+5;
if(i==j)
{

jTextField1.setText(“I and j are unequal”);
}

else

jTextField1.setText(“I and j are equal”)

7. Rewrite the following Java code after underling the corrections made. int x = = 0;

int n= Integer parseInt(Jlabel1.getText);
      Ans:

int n= Integer parseInt(JLabel1.getText());

int x =  0;

8. Find out errors if any:

M=1;

N=0;

For(;m+n<19;++n)

System.out.println(“hello”);
M=m+10;

Ans:

m=1;
n=0;

for(;m+n<19;++n)

System.out.println(“hello”);
m=m+10;

9. The following code has some error(s). Rewrite the correct code underlining all the corrections made.

int y=6,p;

do

{ y=3.14*y;

p=y%10;
if p=2

System.out.print(“Two”);
while(y>1)

Ans:

int y=6,p;
do

{ y=3.14*y;
    p=y%10;
if (p==2)

System.out.print(“Two”);
}while(y>1);

Rewrite questions:

1.     Rewrite the following program code using a for loop:

inti,sum=0;

while(i<10)
{ sum +=i;
i+=2;

}

Ans:        int i,sum=0;

for(i=0;i<10;i+=2)
{ sum +=i;

}

2.   Rewrite the following code using while loop :

inti,j;

for(i=1;i<=4;i++)

{           for(j=1;j<=i;++j)

{           System.out.print(j);

}

System.out.println();
}

Ans:

int i=1,j;

while(i<=4)
{    j=1;

while(j<=i)

{           System.out.print(j);

++j;

}     i++;

System.out.println();

}

3.   Write a equivalent while loop for the following code:

intsz=25;

for(int i=0,sum=0;i<sz;i++)
sum+=i;

System.out.println(sum);

Ans:          int sz=25;

int i=0,sum=0;

while(i<sz)
{

sum+=i;
i++;

}

System.out.println(sum);

4.   Rewrite the following if-else segment using switch-case statement
            char ch='A';

if(ch=='A')

System.out.println("Account");

if((ch=='C') || (ch=='G'))

System.out.println("Admin");
if(ch=='F')

System.out.println("Advisor");

Ans:         char ch='A';

switch(ch)
{

case ‘A':

System.out.println("Account");
break;

case 'C':
case 'G’:

System.out.println("Admin");
break;

case 'F':

System.out.println("Advisor");

}

5.   Rewrite the following code using while loop:
            inti,j;

for(i=1,j=2;i<=6;i++,j+=2)
System.out.println(i++);

System.out.println(“Finished!!!”);

Ans:          inti=1,j=2;

while(i<=6)

{System.out.println(i++);
i++;

j+=2;}

System.out.println(“Finished!!!”);

6.   Rewrite the following code using for loop.

int   i=0;

while(++i<20)

{    if( i==8)

break;

System.out.println(i++);

}

Ans:

int i;

for(i=1;i<20;++i)
       {    if( i==8)

break;

System.out.println(i++);
             }

7.   Rewrite the code using switch statement:

If(k==1)

Day=”Monday”;
elseif(k==2)

Day=”Tuesday”;
elseif(k==3)

Day=”Wednesday”;

else

Day=”-”

Ans:

switch(k)
{

case 1: Day=”Monday”;
break;

case 2: Day=”Tuesday”;
break;

case 3: Day=”Wednesday”;
break;

default: Day=””;
}

8. Write the equivalent switch case for the following code :

If (num1 = =1 )

jTextField1.setText(“Number is one”);
else If (num1 = =2 )

jTextField1.setText(“Number is two”);
else   If (num1 = =3 )

jTextField1.setText(“Number is three”);
else

jTextField1.setText(“Number is more than three”);
Ans:

Switch(num1)
{

Case 1 :

jTextField1.setText(“Number is one”);
break;

case 2 :

jTextField1.setText(“Number is two”);
break;

case 3 :

jTextField1.setText(“Number is three”);
break;

default:

jTextField1.setText(“Number is more than three”);
}

9.   Given the following code fragment :

If(a==0)

System.out.println(“zero”);
If(a==1)

System.out.println(“one”);
If(a==2)

System.out.println(“two”);
If(a==3)

System.out.println(“three”);

Write an alternative code (Using if) that saves on number of comparsons

Ans:

if(a==0)

System.out.println(“zero”);

else if(a==1)

System.out.println(“one”);
else if(a==2)

System.out.println(“two”);

else if(a==3)

System.out.println(“three”);

10. Rewrite the following code fragment using switch :

if(ch = = ‘E’)

east++;

if(ch = = ‘W’)

west++;

if(ch = = ‘N’)

north++;

if(ch = = ‘S’)

south++;

else

jOptionPane.showMessageDialog(null, “unknown”);

Ans:

Switch(ch)
{

Case   ‘E’:
east++;
break;

case   ‘W’:
west++;
break;

case ‘N’:
north++;
break;

case   ‘S’:
south++;
break;

default :

jOptionPane.showMessageDialog(null, “unknown”);
}

11     Rewrite the following code using for loop:

int   i = 0;

while(++i <20)
    {

if(i = = 8)
break;

System.out.println(++i);

}

Ans:

for(int   i = 0;++i <20;)
    {

if(i = = 8)
break;

System.out.println(++i);

}