(i) abstract (ii) final (iii) super (iv) this (v) try (vi)
catch (vii) throw
(viii) throws (ix) finally
2).Explain -classpath and –d option of
javac with example?
3).What are the access specifiers
available in java? Explain each of them. State which of these can be applied to
a class and which can be applied to a member of a package.
4).What is interface? Why it is
required? Explain with example?
5). What is String Buffer? Explain any
5 methods of String Buffer Class with syntax and example?
6).What is wrapper classes? Explain all
in detail?
7).Explain how the concept inheritance
is achieved in java?
8).What is Exception handling? Explain types of exception available in
java?
9).How to create a custom exception in java explain with example?
10).What is chained Exception explain with example? Put Top layer
exception as a IOException and under this add two cause first
ArithmeticException and second ArrayIndexOutOfBoundsException. (Also explain
initCause() and getCause() method.)
11). Explain Inner Class, Top level nested Class, Local Class and
anonymous classes in detail?
12). What is enum type? Explain with example?
13). Explain Collection Framework in detail? Explain all interface extends
from Collection and Map.
What is the
difference between an Interface and an Abstract class?
A:
An
abstract class can have instance methods that implement a default behavior.
An Interface can only declare constants and instance methods, but cannot
implement default behavior and all methods are implicitly abstract. An
interface has all public members and no implementation. An abstract class is
a class which may have the usual flavors of class members (private,
protected, etc.), but has some abstract methods.
.
Q:
What is the
purpose of garbage collection in Java, and when is it used?
A:
The
purpose of garbage collection is to identify and discard objects that are no
longer needed by a program so that their resources can be reclaimed and
reused. A Java object is subject to garbage collection when it becomes
unreachable to the program in which it is used.
Q:
What are pass
by reference and passby value?
A:
Pass By Reference
means the passing the address itself rather than passing the value.
Passby Value means passing a copy of the value to be passed.
Q:
What is the
difference between a constructor and a method?
A:
A
constructor is a member function of a class that is used to create objects of
that class. It has the same name as the class itself, has no return type, and
is invoked using the new operator.
A method is an ordinary member function of a class. It has its own name, a
return type (which may be void), and is invoked using the dot operator.
Q:
State
the significance of public, private, protected, default modifiers both singly
and in combination and state the effect of package relationships on declared
items qualified by these modifiers.
A:
public
: Public
class is visible in other packages, field is visible everywhere (class must
be public too) private :
Private variables or methods may be used only by an instance of the same
class that declares the variable or method, A private feature may only be
accessed by the class that owns the feature. protected :
Is available to all classes in the same package and also available to all
subclasses of the class that owns the protected feature.This access is
provided even to subclasses that reside in a different package from the class
that owns the protected feature. default :What
you get by default ie, without any access modifier (ie, public private or
protected).It means that it is visible to all within a particular package.
Q:
What is an
abstract class?
A:
Abstract
class must be extended/subclassed (to be useful). It serves as a template. A
class that is abstract may not be instantiated (ie, you may not call its
constructor), abstract class may contain static data. Any class with an
abstract method is automatically abstract itself, and must be declared as
such.
A class may be declared abstract even if it has no abstract methods. This
prevents it from being instantiated.
Q:
What is static
in java?
A:
Static
means one per class, not one for each object no matter how many instance of a
class might exist. This means that you can use them without creating an
instance of a class.Static methods are implicitly final, because overriding
is done based on the type of the object, and static methods are attached to a
class, not an object. A static method in a superclass can be shadowed by
another static method in a subclass, as long as the original method was not
declared final. However, you can't override a static method with a nonstatic
method. In other words, you can't change a static method into an instance
method in a subclass.
Q:
What is final?
A:
A final
class can't be extended ie., final class may not be subclassed. A final
method can't be overridden when its class is inherited. You can't change
value of a final variable (is a constant).
Q:
What if the
main method is declared as private?
A:
The
program compiles properly but at runtime it will give "Main method not
public." message.
Q:
What if the
static modifier is removed from the signature of the main method?
A:
Program
compiles. But at runtime throws an error "NoSuchMethodError".
Q:
What if I write
static public void instead of public static void?
A:
Program
compiles and runs properly.
Q:
What if I do
not provide the String array as the argument to the method?
A:
Program
compiles but throws a runtime error "NoSuchMethodError".
Q:
What is the
first argument of the String array in main method?
A:
The
String array is empty. It does not have any element. This is unlike C/C++
where the first element by default is the program name.
Q:
If I do not provide any arguments on the command line, then the
String array of Main method will be empty or null?
A:
It is
empty. But not null.
Q:
How can one
prove that the array is not null but empty using one line of code?
A:
Print
args.length. It will print 0. That means it is empty. But if it would have
been null then it would have thrown a NullPointerException on attempting to
print args.length.
Q:
What environment variables do I need to set on my machine in order
to be able to run Java programs?
A:
CLASSPATH
and PATH are the two variables.
Q:
Can an
application have multiple classes having main method?
A:
Yes it
is possible. While starting the application we mention the class name to be
run. The JVM will look for the Main method only in the class whose name you
have mentioned. Hence there is not conflict amongst the multiple classes
having main method.
Q:
Can I have
multiple main methods in the same class?
A:
No the
program fails to compile. The compiler says that the main method is already
defined in the class.
Q:
Do I need to import java.lang package any time? Why ?
A:
No. It
is by default loaded internally by the JVM.
Q:
Can I import
same package/class twice? Will the JVM load the package twice at runtime?
A:
One can
import the same package or same class multiple times. Neither compiler nor
JVM complains abt it. And the JVM will internally load the class only once no
matter how many times you import the same class.
Q:
What is
Overriding?
A:
When a
class defines a method using the same name, return type, and arguments as a
method in its superclass, the method in the class overrides the method in the
superclass.
When the method is invoked for an object of the class, it is the new
definition of the method that is called, and not the method definition from
superclass. Methods may be overridden to be more public, not more private.
Q:
What are
different types of inner classes?
A:
Nested
-level classes,
Member classes, Local classes,
Anonymous classes
Nested -level
classes-
If you declare a class within a class and specify the static modifier, the
compiler treats the class just like any other -level class.
Any class outside the declaring class accesses the nested class with the
declaring class name acting similarly to a package. eg, outer.inner. -level
inner classes implicitly have access only to static variables.There can also
be inner interfaces. All of these are of the nested -level variety.
Member classes
- Member inner classes are just like other member methods and member
variables and access to the member class is restricted, just like methods and
variables. This means a public member class acts similarly to a nested -level
class. The primary difference between member classes and nested -level
classes is that member classes have access to the specific instance of the
enclosing class.
Local classes -
Local classes are like local variables, specific to a block of code. Their
visibility is only within the block of their declaration. In order for the
class to be useful beyond the declaration block, it would need to implement a
more publicly available interface.Because local classes are not members, the
modifiers public, protected, private, and static are not usable.
Anonymous classes
- Anonymous inner classes extend local inner classes one level further. As anonymous
classes have no name, you cannot provide a constructor.
1). Write a Java application which takes several command line
arguments, which are supposed to be names of students and prints output as
given below: (Suppose we enter 3 names
then output should be as follows):
Number of arguments = 3
1: First Student Name is =Tom
2: Second Student Name is =Dick
3: Third Student Name is =Harry
(Hint: An array may be used for converting
from numeric values from 1 to 20 into String.)
2).
Create an array that stores 20 prices, such as $2.34, $7.89, $1.34, and so on.
Display sum of All the prices. Display all values less than $5.Calculate the
average of the prices and display all the values that are higher than
calculated average value.
3).
A set of 5 words is given. Write a program to reverse each word and arrange the
resulting words in alphabetical order.
4).
A set of 10 names are given. Write a program to delete the first three
characters of the names and arrange the resulting names in alphabetical order
and print them out.
5).
Find the minimum and maximum values in an array.
6).
Demonstrate the use of stack class for characters. Hint(Use array of
Characters)
7). Write a
Menu driven application in java for 2 dimension array.
1). Matrix Addition
2). Matrix Subtraction
3). Matrix Multiplication
8). Develop
same application as in exercise 7 using 3 Dimensional array.
9). Write a
Menu driven application in java that demonstrate a use of Stack and Queue.
(Hint : Use Different class for Stack and Queue)
1)Stack
a.Push
b.Pop
c.Display Stack
d.Quit from stack
2)Queue
a.Insert
b.Delete
c.Display Queue
d.Quit From Queue
3)Exit
10).Write
a class called Statistics, which has a static method called average, which
takes a onedimensional array for double type, as parameter, and prints the
average for the values in the array. Now write a class with the main method,
which creates a two-dimensional array for the four weeks of a month, containing
minimum temperatures for the days of the week(an array of 4 by 7), and uses the
average method of the Statistics class to compute and print the average
temperatures for the four weeks.
