System.out.println("Hello World");
}
}
DATA TYPES AND
CONSTANTS
1) Correct
the variable initializations below:
public
class DefineSomeVariables
{
double
amount = 100.50;
long
population = 9999999999;
}
public
class DefineSomeVariables
{
double amount = 100.50d;
long earthPopulation = 9999999999l;
}
2) What is
the difference between Variable and Constant?
Constants
are basically variables whose value can't change. We use the keyword
final to declare constants like below.
public
final int DAYS = 7;
According
to java convention, the Constant name should be in capital letters always.
OPERATORS
1) Provide
the output of the below code:
public
class SimpleOperations
{
public
static void main(String[] args)
{
double
a = 10.5 % 2;
double
b = 3.5 * 2;
float
c = (float)6.8 / 2;
System.out.println("a
=> " + a + " b => " + b + " => c "
+ c);
}
}
a
=> 0.5 b => 7.0 => c 3.4
2) What is
the data type conversion in Java? Fill in the missing values in the below
code.
double
x = 9.997;
int
nx = (...) x;
When
we assign a value of one data type to another, the two types might not
be compatible with each other. If the data types are compatible, then
Java will perform the conversion automatically known as Automatic
Type Conversion and if not then they need to be cast or converted
explicitly.
double
x = 9.997;
int
nx = (int) x;
3) Fill in
the blank below:
x
+= 4; is equivalent to ...
x
+= 4; is equivalent to x = x + 4;
4) After
execution below statements what would be the value of variables m, n, a
and b:
int
m = 7;
int
n = 7;
int
a = 2 * ++m;
int
b = 2 * n++;
a
= 16, m = 8
B
= 14, n = 8
5) Write down
the result of the below expressions in the form of True and False:
int x = 10;
Int y = 20;
x < y
|
...
|
|
x > y
|
...
|
|
x <= y
|
...
|
|
x >= y
|
...
|
|
x == y
|
...
|
|
x != y
|
...
|
|
x
< y = True
x
> y = False
X
<= y = True
x
>= y = False
x
== y = False
x
!= y = True
ENUMS
1) Why use
Enums instead of Constants? Which is better?
//
Constants for player types
public
static final String ARCHER = "Archer";
public
static final String WARRIOR = "Warrior";
//
Constants for genders
public
static final String MALE = "Male";
public
static final String FEMALE = "Female";
then
you end up not really knowing the type of your data - leading to
potentially incorrect code:
String
playerType = Constants.MALE; // This is wrong but Java will not
complain
if
you use enums, that would end up as:
//
Compile-time error - incompatible types!
PlayerType
playerType = Gender.MALE;
This
is why Enums are better than Constants.
STRING
1) Write down
the output of the below String comparisons:
public
class StringComp
{
public
static void main(String[] args)
{
String
a = "Rahul";
String
b = "Rahul";
String
c = new String("Rahul");
System.out.println("Rahul".equals(a));
System.out.println("Rahul"
== a);
System.out.println(a.equals(b));
System.out.println(a==b);
System.out.println(a.equals(c));
System.out.println(a==c);
}
}
System.out.println("Rahul".equals(a));
// True
System.out.println("Rahul"
== a); // True
System.out.println(a.equals(b));
// True
System.out.println(a==b);
// True
System.out.println(a.equals(c));
// True
System.out.println(a==c);
// False
2) Write down
the output of the below String class methods:
public class StringMethods
{
public static void main(String[] args)
{
String str = "Java
Fundamentals";
System.out.println(str.charAt(5));
System.out.println(str.startsWith("java"));
System.out.println(str.endsWith("tals"));
System.out.println(str.indexOf("men"));
System.out.println(str.lastIndexOf("a"));
System.out.println(str.replace("Fund",
"Coll"));
System.out.println(str.substring(3));
System.out.println(str.substring(1,
5));
System.out.println(str.toLowerCase());
System.out.println(str.toUpperCase());
}
}
System.out.println(str.charAt(5));
// F
System.out.println(str.startsWith("java"));
// false
System.out.println(str.endsWith("tals"));
// true
System.out.println(str.indexOf("men"));
// 10
System.out.println(str.lastIndexOf("a"));
// 14
System.out.println(str.replace("Fund",
"Coll")); // Java Collamentals
System.out.println(str.substring(3));
// a Fundamentals
System.out.println(str.substring(1,
5)); // ava
System.out.println(str.toLowerCase());
// java fundamentals
System.out.println(str.toUpperCase());
// JAVA FUNDAMENTALS
3)
Correct the below code if you see any mistakes?
String str;
// Some code here
if(str.length != 0 && str !=
null)
{
//Do something here
}
String str;
// Some code here
if(str != null &&
str.length != 0)
{
//Do something
here
}
SCANNER / COMMAND
LINE INPUT
1) Complete
the below code which is used to take input from the command line:
public
class CommandLineInput
{
public
static void main(String args[])
{
Scanner
in = new Scanner(.....); // Code missing here
System.out.print("What is your
name? ");
String
name = …………………………….. // code missing here
System.out.print("Your name is:
"+name);
//Get second input
System.out.print("How old are you?
");
int
age = ……………………………………. // code missing
here
System.out.print("Your age is:
"+age);
}
}
public
class CommandLineInput
{
public static void main(String
args[])
{
Scanner in = new
Scanner(System.in);
System.out.print("What is
your name? ");
String name = in.nextLine();
System.out.print("Your name
is: "+name);
//Get second input
System.out.print("How old
are you? ");
int age = in.nextInt();
System.out.print("Your age
is: "+age);
}
}
BLOCK SCOPE
1) Fill in
the blanks:
class
Test
{
private int x;
public void setX(int x)
{
// set the x argument variable value in instance field x
………………………………………….
}
}
class
Test
{
private int x;
public void setX(int x)
{
// set the x argument variable value in instance field x
This.x = x;
}
}
2) Write the
output of the below program:
public
class Test
{
static int x = 11;
private int y = 33;
public void method1(int x)
{
Test t = new Test();
this.x = 22;
y = 44;
System.out.println("Test.x:
" + Test.x);
System.out.println("t.x: "
+ t.x);
System.out.println("t.y: "
+ t.y);
System.out.println("y: "
+ y);
}
public static void main(String
args[])
{
Test t = new Test();
t.method1(5);
}
}
Test.x:
22
t.x: 22
t.y: 33
Y: 44
LOOPS
1) Can for
and while loop be infinite? If yes, implement the code.
Yes,
We can have infinite for and while loops.
while(true)
{
//This code execution will be infinite
}
for(;;)
{
//This code execution will be infinite
}
2) Correct
the below code so that the below program print number 1 to 10:
int
i = 0;
for(i<10;)
{
System.out.println(i);
}
int
i = 1;
for(;i<=10;
i++)
{
System.out.println(i);
}
ARRAY
1) What type
of error is in the below code? Compile time or run time? Fix the error and
rewrite that code block.
class
ArrayExample
{
public
static void main (String[] args)
{
int[]
arr = new int[2];
arr[0]
= 10;
arr[1]
= 20;
for
(int i = 0; i <= arr.length; i++)
System.out.println(arr[i]);
}
}
It
is a Runtime
error. This
program will throw ArrayIndexOutOfboundException.
We
have to correct the loop condition like the below:
for
(int i = 0; i < arr.length; i++)
System.out.println(arr[i]);
2) Fill in
the blanks so that only indexes of even number gets printed:
public
void arrayExample()
{
int[]
a = new int[10];
int
length = a.length;
for
(int i = 0; i < a.length; i++)
a[i]
= i+10;
//Print the array
for
(int i = 0; i < a.length; ...) // you have to change here in the
code
System.out.println(a[i]);
}
public
void arrayExample()
{
int[] a = new int[10];
int length = a.length;
for (int i = 0; i < a.length; i++)
a[i] = i+10;
// print the array
for (int i = 0; i < a.length; i+=2)
// you have to change here in the code
System.out.println(a[i]);
}
3) What would
be the output of the following program where we are copying an array.
class
TestArrayCopyDemo {
public
static void main(String[] args) {
char[]
copyFrom = { 'd', 'e', 'c', 'a', 'f', 'f', 'e',
'i',
'n', 'a', 't', 'e', 'd' };
char[]
copyTo = new char[7];
System.arraycopy(copyFrom, 2, copyTo, 0,
7);
System.out.println(String.valueOf(copyTo));
}
}
caffeine
CLASSES AND
OBJECTS
1) Identify
the issues and fix those:
public
class Employee
{
String
name;
int salary;
void
Employee(String name, int salary) // you can find a issue here
{
this.name
= name;
this.salary
= salary;
}
private
int calulateTax()
{
//
you can find an issue here
static
int tax = 10; // This is the percent;
return
salary * 10 / 100;
}
public
static void main(String[] args)
{
Employee
e = new Employee("Rahul", 1000);
System.out.println(e.calulateTax());
}
}
public
class Employee
{
String
name;
int salary;
Employee(String
name, int salary)
{
this.name
= name;
this.salary
= salary;
}
private
int calulateTax()
{
int
tax = 10; // This is the percent;
return
salary * 10 / 100;
}
public
static void main(String[] args)
{
Employee
e = new Employee("Rahul", 1000);
System.out.println(e.calulateTax());
}
}
2) Fill in
the blanks so that puppy’s age gets printed on the console
public
class Puppy
{
int puppyAge;
public Puppy(String name)
{
System.out.println("Name chosen is :" + name );
}
public void setAge( int age )
{
puppyAge = age;
}
public int getAge()
{
System.out.println("Puppy's age is :" + puppyAge );
return puppyAge;
}
public static void
main(String []args)
{
Puppy myPuppy = new Puppy( "tommy" );
myPuppy.setAge( 2 );
/* Call another class method to get
puppy's age, add code here */
…………………………………………………………...
}
}
public
class Puppy
{
int puppyAge;
public Puppy(String name)
{
System.out.println("Name
chosen is :" + name );
}
public void setAge( int
age )
{
puppyAge = age;
}
public int getAge()
{
System.out.println("Puppy's
age is :" + puppyAge );
return puppyAge;
}
public static void main(String []args)
{
Puppy myPuppy = new Puppy(
"tommy" );
myPuppy.setAge( 2 );
/*
Call another class method to get puppy's age, add code here */
myPuppy.getAge( );
}
}
STATIC METHODS
1) Correct
the method declaration so that we can call that statically:
public
class StaticMethodExample
{
public void getListofFriuts()
{
// do something here
}
public static void main(String[] args)
{
StaticMethodExample.getListofFriuts();
}
}
public
class StaticMethodExample
{
public static void
getListofFruits()
{
// do something
here
}
public static void
main(String[] args)
{
StaticMethodExample.getListofFruits();
}
}
2) What is
wrong with the below code? I just want to call one constructor from another
using this keyword
public
Employee(double s)
{
nextId++;
this("Employee #" + nextId,
s);
}
this
keyword statement should be the first line in the constructor like below:
public
Employee(double s)
{
this("Employee
#" + nextId, s);
nextId++;
}
SPECIFIC CODE
BLOCKS
1) What would
be the output of the following code?
public class
Employee
{
private static int nextId;
private int id;
private String name;
private double salary;
static {
System.out.println(“This is the static block”);
}
// object initialization block
{
System.out.println(“This is the initialization block”);
id = nextId;
nextId++;
}
public Employee(String n, double s)
{
System.out.println(“This is the two argument constructor”);
name = n;
salary = s;
}
public Employee()
{
System.out.println(“This is the no argument constructor”);
name = "";
salary = 0;
}
public static void main(String[] args)
{
Employee e = new Employee();
}
}
This
is the static block
This is the initialization block
This is
the no argument constructor
INHERITANCE
1) What is the benefit of inheritance? How can we call the parent class constructor from the child class?
The main benefit of
inheritance is code reusability. We can call the parent class constructor
using the super keyword.
2) What is
the error in below code? Correct that.
class
MountainBike extends Bicycle
{
public
int seatHeight;
public
MountainBike(int gear,int speed, int startHeight)
{
seatHeight = startHeight;
super(gear,
speed);
}
public
void setHeight(int newValue)
{
seatHeight
= newValue;
}
}
public
MountainBike(int gear,int speed, int startHeight)
{
super(gear, speed);
seatHeight = startHeight;
}
super
keyword call can be used as first-line inside a constructor.
3) How can we
make sure that no one can extend a particular class?
Using
final keyword. If we add final keyword before the class name then that
class can not be extended by any class.
public
final class Utility
{
}
4) Modify the
below code so that no one can override the below method in any child
class.
public
void noOneCanOverrideMe()
{
}
public
final void noOneCanOverrideMe()
{
}