Objective interview questions and answers on java and c
Objective interview questions and answers on java and c also related with php and mysql objective question like oops
Objective Interview Questions and Answers on java are given below
Questions 1.The
Java interpreter is used for the execution of the source code.
a)True b) False Answers : a. Questions 2) On successful compilation a file with the class extension is created.
a)True b) False Answers : a. Questions 3) The Java source code can be created in a Notepad editor.
a)True b) False Answers : a. Questions 4) The Java Program is enclosed in a class definition.
a)True b) False Answers : a. Questions 5) What declarations are required for every Java application? Answers : A class and the main( ) method declarations. Questions 6) What are the two parts in executing a Java program and their purposes? Answers : Two parts in executing a Java program are:
Java Compiler and Java Interpreter.
The Java Compiler is used for compilation and the Java Interpreter is used
for execution of the application. Questions7) What are the three OOPs principles and define them? Answers : Encapsulation, Inheritance and Polymorphism are the three OOPs
Principles.
Encapsulation:
Is the Mechanism that binds together code and the data it manipulates, and
keeps both safe from outside interference and misuse.
Inheritance:
Is the process by which one object acquires the properties of another
object.
Polymorphism:
Is a feature that allows one interface to be used for a general class of
actions.
Questions 8) What is a compilation unit? Answers : Java source code file. Questions9) What output is displayed as the result of executing the following
statement?
System.out.println("// Looks like a comment.");
// Looks like a comment
The statement results in a compilation error
Looks like a comment
No output is displayed Answers : a. Questions 10) In order for a source code file, containing the public class Test, to
successfully compile, which of the following must be true?
It must have a package statement
It must be named Test.java
It must import java.lang
It must declare a public class named Test Answers : b Questions 11) What are identifiers and what is naming convention? Answers : Identifiers are used for class names, method names and variable
names. An identifier may be any descriptive sequence of upper case &
lower case letters,numbers or underscore or dollar sign and must not begin
with numbers. Questions 12) What is the return type of program’s main( ) method? Answers : void Questions 13) What is the argument type of program’s main( ) method? Answers : string array. Questions 14) Which characters are as first characters of an identifier? Answers : A – Z, a – z, _ ,$ Questions 15) What are different comments? Answers : 1) // -- single line comment
2) /* --
*/ multiple line comment
3) /** --
*/ documentation Questions 16) What is the difference between constructor method and method? Answers : Constructor will be automatically invoked when an object is created.
Whereas method has to be call explicitly. Questions 17) What is the use of bin and lib in JDK? Answers : Bin contains all tools such as javac, applet viewer, awt tool etc.,
whereas Lib
contains all packages and variables.
Java Data types,variables and Arrays questions with answers
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Questions 1) What is meant by variable? Answers : Variables are locations in memory that can hold values. Before
assigning any value to a variable, it must be declared. Questions 2) What are the kinds of variables in Java? What are their uses? Answers : Java has three kinds of variables namely, the instance variable, the
local variable and the class variable.
Local variables are used inside blocks as counters or in methods as
temporary variables and are used to store information needed by a single
method.
Instance variables are used to define attributes or the state of a
particular object and are used to store information needed by multiple
methods in the objects.
Class variables are global to a class and to all the instances of the class
and are useful for communicating between different objects of all the same
class or keeping track of global states. Questions3) How are the variables declared? Answers : Variables can be declared anywhere in the method definition and can be
initialized during their declaration.They are commonly declared before
usage at the beginning of the definition.
Variables with the same data type can be declared together. Local variables
must be given a value before usage. Questions 4) What are variable types? Answers : Variable types can be any data type that java supports, which includes
the eight primitive data types, the name of a class or interface and an
array. Questions 5) How do you assign values to variables? Answers : Values are assigned to variables using the assignment operator =. Questions 6) What is a literal? How many types of literals are there? Answers : A literal represents a value of a certain type where the type
describes how that value behaves.
There are different types of literals namely number literals, character
literals,
boolean literals, string literals,etc. Questions 7) What is an array? Answers : An array is an object that stores a list of items. Questions 8) How do you declare an array? Answers : Array variable indicates the type of object that the array holds.
Ex: int arr[]; Questions 9) Java supports multidimensional arrays.
a)True
b)False Answers : a. Questions 10) An array of arrays can be created.
a)True
b)False Answers : a. Questions 11) What is a string? Answers : A combination of characters is called as string. Questions12) Strings are instances of the class String.
a)True
b)False Answers : a. Questions 13) When a string literal is used in the program, Java automatically
creates instances of the string class.
a)True
b)False Answers : a. Questions 14) Which operator is to create and concatenate string? Answers : Addition operator(+). Questions15) Which of the following declare an array of string objects?
String[ ] s;
String [ ]s:
String[ s]:
String s[ ]: Answers : a, b and d Questions16) What is the value of a[3] as the result of the following array
declaration?
1
2
3
4 Answers : d Questions 17) Which of the following are primitive types?
byte
String
integer
Float Answers : a.
18) What is the range of the char type?
0 to 216
0 to 215
0 to 216-1
0 to 215-1
Ans. d Questions19) What are primitive data types? Answers : byte, short, int, long
float, double
boolean
char Questions 20) What are default values of different primitive types? Answers : int - 0
short - 0
byte - 0
long - 0 l
float - 0.0 f
double - 0.0 d
boolean - false
char - null Questions21) Converting of primitive types to objects can be explicitly.
a)True
b)False Answers : b. Questions 22) How do we change the values of the elements of the array? Answers : The array subscript expression can be used to change the values of
the elements of the array. Questions 23) What is final varaible? Answers : If a variable is declared as final variable, then you can not change
its value. It becomes constant. Questions 24) What is static variable? Answers : Static variables are shared by all instances of a class.
Java Operators interview questions with answers
Questions 1) What are operators and what are the various types of operators available
in Java? Answers : Operators are special symbols used in expressions.
The following are the types of operators:
Arithmetic operators,
Assignment operators,
Increment & Decrement operators,
Logical operators,
Biwise operators,
Comparison/Relational operators and
Conditional operators Questions 2) The ++ operator is used for incrementing and the -- operator is used for
decrementing.
a)True
b)False Answers : a. Questions3) Comparison/Logical operators are used for testing and magnitude.
a)True
b)False Answers : a. Questions4) Character literals are stored as unicode characters.
a)True
b)False Answers : a. Questions5) What are the Logical operators? Answers : OR(|), AND(&), XOR(^) AND NOT(~). Questions6) What is the % operator? Answers : % operator is the modulo operator or reminder operator. It returns
the reminder of dividing the first operand by second operand.
7) What is the value of 111 % 13?
3
5
7
9 Answers : c. Questions8) Is &&= a valid operator? Answers : No. Questions9) Can a double value be cast to a byte? Answers : Yes Questions 10) Can a byte object be cast to a double value ? Answers : No. An object cannot be cast to a primitive value. Questions 11) What are order of precedence and associativity? Answers : Order of precedence the order in which operators are evaluated in
expressions.
Associativity determines whether an expression is evaluated left-right or
right-left. Questions12) Which Java operator is right associativity? Answers : = operator. Questions 13) What is the difference between prefix and postfix of -- and ++
operators? Answers : The prefix form returns the increment or decrement operation and
returns the value of the increment or decrement operation.
The postfix form returns the current value of all of the expression and
then
performs the increment or decrement operation on that value. Questions14) What is the result of expression 5.45 + "3,2"?
The double value 8.6
The string ""8.6"
The long value 8.
The String "5.453.2" Answers : d Questions 15) What are the values of x and y ?
x = 5; y = ++x; Answers : x = 6; y = 6 Questions 16) What are the values of x and z?
x = 5; z = x++; Answers : x = 6; z = 5
Java Control Statements inteview questions and answers
Questions 1) What are the programming constructs? Answers : a) Sequential
b) Selection -- if and switch statements
c) Iteration -- for loop, while loop and do-while loop
2) class conditional {
public static void main(String args[]) {
int i = 20;
int j = 55;
int z = 0;
z = i < j ? i : j; // ternary operator
System.out.println("The value assigned is " + z);
}
}
What is output of the above program? Answers : The value assigned is 20 Questions3) The switch statement does not require a break.
a)True
b)False Answers : b. Questions4) The conditional operator is otherwise known as the ternary operator.
a)True
b)False Answers : a. Questions5) The while loop repeats a set of code while the condition is false.
a)True
b)False Answers : b. Questions6) The do-while loop repeats a set of code atleast once before the
condition is tested.
a)True
b)False Answers : a. Questions 7) What are difference between break and continue? Answers : The break keyword halts the execution of the current loop and forces
control out of the loop.
The continue is similar to break, except that instead of halting the
execution of the loop, it starts the next iteration.
Questions8) The for loop repeats a set of statements a certain number of times until
a condition is matched.
a)True
b)False Answers : a. Questions9) Can a for statement loop indefintely? Answers : Yes. Questions10) What is the difference between while statement and a do statement/ Answers : A while statement checks at the beginning of a loop to see whether
the next loop iteration should occur.
A do statement checks at the end of a loop to see whether the next
iteration of a loop should occur. The do statement will always execute the
body of a loop at least once.
Interview questions on java Classes and Methods
Questions1) Which is used to get the value of the instance variables? Answers : Dot notation. Questions2) The new operator creates a single instance named class and returns a
reference to that object.
a)True
b)False Answers : a. Questions3) A class is a template for multiple objects with similar features.
a)True
b)False Answers : a. Questions 4) What is mean by garbage collection? Answers : When an object is no longer referred to by any variable, Java
automatically
reclaims memory used by that object. This is known as garbage collection. Questions5) What are methods and how are they defined? Answers : Methods are functions that operate on instances of classes in which
they are defined.Objects can communicate with each other using methods and
can call methods in other classes.
Method definition has four parts. They are name of the method, type of
object or primitive type the method returns, a list of parameters and the
body of the method.
A method's signature is a combination of the first three parts mentioned
above. Questions6) What is calling method? Answers : Calling methods are similar to calling or referring to an instance
variable. These methods are accessed using dot notation.
Ex: obj.methodname(param1,param2) Questions7) Which method is used to determine the class of an object? Answers : getClass( ) method can be used to find out what class the belongs to.
This class is defined in the object class and is available to all objects. Questions 8) All the classes in java.lang package are automatically imported when
a program is compiled.
a)True
b)False Answers : a. Questions 9) How can class be imported to a program? Answers : To import a class, the import keyword should be used as shown.;
import classname; Questions 10) How can class be imported from a package to a program? Answers : import java . packagename . classname (or) import java.package name.*; Questions 11) What is a constructor? Answers : A constructor is a special kind of method that determines how an
object is
initialized when created. Questions 12) Which keyword is used to create an instance of a class? Answers : new. Questions 13) Which method is used to garbage collect an object? Answers : finalize (). Questions 14) Constructors can be overloaded like regular methods.
a)True
b)False Answers : a. Questions 15) What is casting? Answers : Casting is bused to convert the value of one type to another.
Questions 16) Casting between primitive types allows conversion of one primitive type
to another.
a)True
b)False Answers : a. Questions 17) Casting occurs commonly between numeric types.
a)True
b)False Answers : a. Questions 18) Boolean values can be cast into any other primitive type.
a)True
b)False Answers : b. Questions 19) Casting does not affect the original object or value.
a)True
b)False Answers : a. Questions 20) Which cast must be used to convert a larger value into a smaller one? Answers : Explicit cast. Questions 21) Which cast must be used to cast an object to another class? Answers : Specific cast. Questions 22) Which of the following features are common to both Java & C++?
A.The class declaration
b.The access modifiers
c.The encapsulation of data & methods with in objects
d.The use of pointers Answers : a,b,c. Questions 23) Which of the following statements accurately describe the use of access
modifiers within a class definition?
a.They can be applied to both data & methods
b.They must precede a class's data variables or methods
c.They can follow a class's data variables or methods
d.They can appear in any order
e.They must be applied to data variables first and then to methods Answers : a,b,d. Questions 24) Suppose a given instance variable has been declared private.
Can this instance variable be manipulated by methods out side its class?
a.yes
b.no Answers : b. Questions 25) Which of the following statements can be used to describe a public
method?
a.It is accessible to all other classes in the hierarchy
b.It is accessablde only to subclasses of its parent class
c.It represents the public interface of its class
d.The only way to gain access to this method is by calling one of the
public class
methods Answers : a,c. Questions 26) Which of the following types of class members can be part of the
internal part of a class?
a.Public instance variables
b.Private instance variables
c.Public methods
d.Private methods Answers : b,d. Questions 27) You would use the ____ operator to create a single instance of a named
class.
a.new
b.dot Answers : a. Questions 28) Which of the following statements correctly describes the relation
between an object and the instance variable it stores?
a.Each new object has its own distinctive set of instance variables
b.Each object has a copy of the instance variables of its class
c.the instance variable of each object are seperate from the variables of
other objects
d.The instance variables of each object are stored together with the
variables of other objects Answers : a,b,c. Questions 29) If no input parameters are specified in a method declaration then the
declaration will include __.
a.an empty set of parantheses
b.the term void Answers : a. Questions 30) What are the functions of the dot(.) operator?
a.It enables you to access instance variables of any objects within a class
b.It enables you to store values in instance variables of an object
c.It is used to call object methods
d.It is to create a new object Answers : a,b,c. Questions 31) Which of the following can be referenced by this variable?
a.The instance variables of a class only
b.The methods of a class only
c.The instance variables and methods of a class Answers : c. Questions 32) The this reference is used in conjunction with ___methods.
a.static
b.non-static Answers : b. Questions 33) Which of the following operators are used in conjunction with the this
and super references?
a.The new operator
b.The instanceof operator
c.The dot operator Answers : c. Questions 34) A constructor is automatically called when an object is instantiated
a. true
b. false Answers : a. Questions 35) When may a constructor be called without specifying arguments?
a. When the default constructor is not called
b. When the name of the constructor differs from that of the class
c. When there are no constructors for the class Answers : c. Questions 36) Each class in java can have a finalizer method
a. true
b.false Answers : a. Questions 37) When an object is referenced, does this mean that it has been
identified by the finalizer method for garbage collection?
a.yes
b.no Answers : b. Questions 38) Because finalize () belongs to the java.lang.Object class, it is
present in all ___.
a.objects
b.classes
c.methods Answers : b. Questions 39) Identify the true statements about finalization.
a.A class may have only one finalize method
b.Finalizers are mostly used with simple classes
c.Finalizer overloading is not allowed Answers : a,c. Questions 40) When you write finalize() method for your class, you are overriding a
finalizer
inherited from a super class.
a.true
b.false Answers : a. Questions 41) Java memory management mechanism garbage collects objects which are no
longer referenced
a true
b.false Answers : a. Questions 42) are objects referenced by a variable candidates for garbage collection
when the variable goes out of scope?
a yes
b. no Answers : a. Questions 43) Java's garbage collector runs as a ___ priority thread waiting for
__priority threads to relinquish the processor.
a.high
b.low Answers : a,b. Questions 44) The garbage collector will run immediately when the system is out of
memory
a.true
b.false Answers : a. Questions 45) You can explicitly drop a object reference by setting the value of a
variable whose data type is a reference type to ___ Answers : null Questions 46) When might your program wish to run the garbage collecter?
a. before it enters a compute-intense section of code
b. before it enters a memory-intense section of code
c. before objects are finalized
d. when it knows there will be some idle time Answers : a,b,d Questions 47) For externalizable objects the class is solely responsible for the
external format of its contents
a.true
b.false Answers : a Questions 48) When an object is stored, are all of the objects that are reachable
from that object stored as well?
a.true
b.false Answers : a Questions 49) The default__ of objects protects private and trancient data, and
supports the __ of the classes
a.evolution
b.encoding Answers : b,a. Questions 50) Which are keywords in Java?
a) NULL
b) sizeof
c) friend
d) extends
e) synchronized Answers : d and e Questions 51) When must the main class and the file name coincide? Answers :When class is declared public. Questions 52) What are different modifiers? Answers : public, private, protected, default, static, trancient, volatile, final,
abstract. Questions 53) What are access modifiers? Answers : public, private, protected, default. Questions 54) What is meant by "Passing by value" and " Passing by
reference"? Answers : objects – pass by referrence
Methods - pass by value Questions 55) Is a class a subclass of itself? Answers : A class is a subclass itself.
Questions 56) What modifiers may be used with top-level class? Answers : public, abstract, final. Questions 57) What is an example of polymorphism?
Inner class
Anonymous classes
Method overloading
Method overriding Answers : c
java Packages and interface interview questions
1) What are packages ? what is use of packages ? Answers :The package statement defines a name space in which classes are
stored.If you omit the package, the classes are put into the default
package.
Signature... package pkg;
Use: * It specifies to which package the classes defined in a file belongs
to. * Package is both naming and a visibility control mechanism.
2) What is difference between importing "java.applet.Applet" and
"java.applet.*;" ? Answers :"java.applet.Applet" will import only the class Applet from
the package java.applet
Where as "java.applet.*" will import all the classes from
java.applet package.
3) What do you understand by package access specifier? Answers : public: Anything declared as public can be accessed from anywhere
private: Anything declared in the private can’t be seen outside of its
class.
default: It is visible to subclasses as well as to other classes in the
same package.
4) What is interface? What is use of interface? Answers : It is similar to class which may contain method’s signature only but
not bodies.
Methods declared in interface are abstract methods. We can implement many
interfaces on a class which support the multiple inheritance.
5) Is it is necessary to implement all methods in an interface? Answers : Yes. All the methods have to be implemented.
6) Which is the default access modifier for an interface method? Answers : public.
7) Can we define a variable in an interface ?and what type it should be ? Answers : Yes we can define a variable in an interface. They are implicitly
final and static.
8) What is difference between interface and an abstract class? Answers : All the methods declared inside an Interface are abstract. Where as
abstract class must have at least one abstract method and others may be
concrete or abstract.
In Interface we need not use the keyword abstract for the methods.
9) By default, all program import the java.lang package.
True/False Answers : True
10) Java compiler stores the .class files in the path specified in
CLASSPATH
environmental variable.
True/False Answers : False
11) User-defined package can also be imported just like the standard
packages.
True/False Answers : True
12) When a program does not want to handle exception, the ______class is
used. Answers : Throws
13) The main subclass of the Exception class is _______ class. Answers : RuntimeException
14) Only subclasses of ______class may be caught or thrown. Answers : Throwable
15) Any user-defined exception class is a subclass of the _____ class. Answers : Exception
16) The catch clause of the user-defined exception class should ______ its
Base class catch clause. Answers : Exception
17) A _______ is used to separate the hierarchy of the class while
declaring an
Import statement. Answers : Package
18) All standard classes of Java are included within a package called
_____. Answers : java.lang
19) All the classes in a package can be simultaneously imported using ____. Answers : *
20) Can you define a variable inside an Interface. If no, why? If yes, how?
Ans.: YES. final and static
21) How many concrete classes can you have inside an interface?
Ans.: None
22) Can you extend an interface?
Ans.: Yes
23) Is it necessary to implement all the methods of an interface while
implementing the interface?
Ans.: No
24) If you do not implement all the methods of an interface while
implementing , what specifier should you use for the class ?
Ans.: abstract
25) How do you achieve multiple inheritance in Java? Answers : Using interfaces.
26) How to declare an interface example? Answers : access class classname implements interface.
27) Can you achieve multiple interface through interface?
a)True
b) false Answers : a.
28) Can variables be declared in an interface ? If so, what are the
modifiers? Answers : Yes. final and static are the modifiers can be declared in an
interface.
29) What are the possible access modifiers when implementing interface
methods? Answers : public.
30) Can anonymous classes be implemented an interface? Answers : Yes.
31) Interfaces can’t be extended.
a)True
b)False Answers : b.
32) Name interfaces without a method? Answers : Serializable, Cloneble & Remote.
33) Is it possible to use few methods of an interface in a class ? If so,
how? Answers : Yes. Declare the class as abstract.
Java Exception Handling interview questions
Questions 1) What is the difference between ‘throw’ and ‘throws’ ?And it’s
application? Answers : Exceptions that are thrown by java runtime systems can be handled by
Try and catch blocks. With throw exception we can handle the exceptions
thrown by the program itself. If a method is capable of causing an
exception that it does not
handle, it must specify this behavior so the callers of the method can guard
against that exception. Questions 2) What is the difference between ‘Exception’ and ‘error’ in java? Answers : Exception and Error are the subclasses of the Throwable class.
Exception class is used for exceptional conditions that user program should
catch. With exception class we can subclass to create our own custom
exception.
Error defines exceptions that are not excepted to be caught by you program.
Example is Stack Overflow. Questions 3) What is ‘Resource leak’? Answers : Freeing up other resources that might have been allocated at the
beginning of a method. Questions 4)What is the ‘finally’ block? Answers : Finally block will execute whether or not an exception is thrown. If
an exception is thrown, the finally block will execute even if no catch
statement match the exception. Any time a method is about to return to the
caller from inside try/catch block, via an uncaught exception or an
explicit return statement, the finally clause is also execute. Questions5) Can we have catch block with out try block? If so when? Answers : No. Try/Catch or Try/finally form a unit. Questions 6) What is the difference between the following statements?
Catch (Exception e),
Catch (Error err),
Catch (Throwable t) Answers :
Questions 7) What will happen to the Exception object after exception handling? Answers : It will go for Garbage Collector. And frees the memory. Questions 8) How many Exceptions we can define in ‘throws’ clause? Answers : We can define multiple exceptions in throws clause.
Signature is..
type method-name (parameter-list) throws exception-list
Questions 9) The finally block is executed when an exception is thrown, even if no
catch matches it.
True/False Answers : True Questions 10) The subclass exception should precede the base class exception when
used within the catch clause.
True/False Answers : True Questions 11) Exceptions can be caught or rethrown to a calling method.
True/False Answers : True Questions 12) The statements following the throw keyword in a program are not
executed.
True/False Answers : True Questions 13) The toString ( ) method in the user-defined exception class is
overridden.
True/False Answers : True
Jave MULTI THREADING interview questions with Answers
Questions 1) What are the two types of multitasking? Answers : 1.process-based
2.Thread-based Questions2) What are the two ways to create the thread? Answers : 1.by implementing Runnable
2.by extending Thread Questions 3) What is the signature of the constructor of a thread class? Answers : Thread(Runnable threadob,String threadName) Questions 4) What are all the methods available in the Runnable Interface? Answers : run() Questions 5) What is the data type for the method isAlive() and this method is
available in which class? Answers : boolean, Thread Questions 6) What are all the methods available in the Thread class? Answers : 1.isAlive()
2.join()
3.resume()
4.suspend()
5.stop()
6.start()
7.sleep()
8.destroy()
7) What are all the methods used for Inter Thread communication and what is
the class in which these methods are defined? Answers :1. wait(),notify() & notifyall()
2. Object class
8) What is the mechanisam defind by java for the Resources to be used by
only one Thread at a time? Answers : Synchronisation
9) What is the procedure to own the moniter by many threads? Answers : not possible
10) What is the unit for 1000 in the below statement?
ob.sleep(1000) Answers : long milliseconds
11) What is the data type for the parameter of the sleep() method? Answers : long
12) What are all the values for the following level?
max-priority
min-priority
normal-priority Answers : 10,1,5
13) What is the method available for setting the priority? Answers : setPriority()
14) What is the default thread at the time of starting the program? Answers : main thread
15) The word synchronized can be used with only a method.
True/ False Answers : False
16) Which priority Thread can prompt the lower primary Thread? Answers : Higher Priority
17) How many threads at a time can access a monitor? Answers : one
18) What are all the four states associated in the thread? Answers : 1. new 2. runnable 3. blocked 4. dead
19) The suspend()method is used to teriminate a thread?
True /False Answers : False
20) The run() method should necessary exists in clases created as subclass
of thread?
True /False Answers : True
21) When two threads are waiting on each other and can't proceed the programe
is said to be in a deadlock?
True/False Answers : True
22) Which method waits for the thread to die ? Answers : join() method
23) Which of the following is true?
1) wait(),notify(),notifyall() are defined as final & can be called
only from with in a synchronized method
2) Among wait(),notify(),notifyall() the wait() method only throws
IOException
3) wait(),notify(),notifyall() & sleep() are methods of object class
1
2
3
1 & 2
1,2 & 3 Answers : D
24) Garbage collector thread belongs to which priority? Answers : low-priority
25) What is meant by timeslicing or time sharing? Answers : Timeslicing is the method of allocating CPU time to individual
threads in a priority schedule.
26) What is meant by daemon thread? In java runtime, what is it's role? Answers : Daemon thread is a low priority thread which runs intermittently in
the background doing the garbage collection operation for the java runtime
system.
Java Inheritance interview questions with answers
Questions 1) What is the difference between superclass & subclass? Answers : A super class is a class that is inherited whereas subclass is a
class that does the inheriting. Questions 2) Which keyword is used to inherit a class? Answers : extends Questions 3) Subclasses methods can access superclass members/ attributes at all
times?
True/False Answers : False
Questions 4) When can subclasses not access superclass members? Answers : When superclass is declared as private. Questions 5) Which class does begin Java class hierarchy? Answers : Object class Questions 6) Object class is a superclass of all other classes?
True/False Answers : True Questions 7) Java supports multiple inheritance?
True/False Answers : False Questions 8) What is inheritance? Answers : Deriving an object from an existing class. In the other words,
Inheritance is the process of inheriting all the features from a class Questions 9) What are the advantages of inheritance? Answers : Reusability of code and accessibility of variables and methods of the
superclass by subclasses. Questions10) Which method is used to call the constructors of the superclass from
the subclass? Answers : super(argument) Questions 11) Which is used to execute any method of the superclass from the
subclass? Answers : super.method-name(arguments) Questions 12) Which methods are used to destroy the objects created by the
constructor methods? Answers : finalize() Questions 13) What are abstract classes? Answers : Abstract classes are those for which instances can’t be created. Questions 14) What must a class do to implement an interface? Answers : It must provide all of the methods in the interface and identify the
interface in its implements clause. Questions 15) Which methods in the Object class are declared as final? Answers : getClass(), notify(), notifyAll(), and wait() Questions 16) Final methods can be overridden.
True/False Answers : False Questions 17) Declaration of methods as final results in faster execution of the
program?
True/False Answers : True Questions 18) Final variables should be declared in the beginning?
True/False Answers : True Questions 19) Can we declare variable inside a method as final variables? Why? Answers : Cannot because, local variable cannot be declared as final variables. Questions20) Can an abstract class may be final? Answers : An abstract class may not be declared as final. Questions 21) Does a class inherit the constructors of it's super class? Answers : A class does not inherit constructors from any of it's super classes. Questions 22) What restrictions are placed on method overloading? Answers : Two methods may not have the same name and argument list but different
return types. Questions 23) What restrictions are placed on method overriding? Answers : Overridden methods must have the same name , argument list , and
return type. The overriding method may not limit the access of the method
it overridees.The overriding method may not throw any exceptions that may
not be thrown by the overridden method. Questions 24) What modifiers may be used with an inner class that is a member of an
outer class? Answers : a (non-local) inner class may be declared as public, protected,
private, static, final or abstract. Questions 25) How this() is used with constructors? Answers : this() is used to invoke a constructor of the same class Questions 26) How super() used with constructors? Answers : super() is used to invoke a super class constructor Questions 27) Which of the following statements correctly describes an interface?
a)It's a concrete class
b)It's a superclass
c)It's a type of abstract class Answers : c
28) An interface contains __ methods
a)Non-abstract
b)Implemented
c)unimplemented Answers :c
STRING
HANDLING
Which package does define String and StringBuffer classes? Answers : java.lang package.
Which method can be used to obtain the length of the String? Answers : length( ) method.
How do you concatenate Strings? Answers : By using " + " operator.
Which method can be used to compare two strings for equality? Answers : equals( ) method.
Which method can be used to perform a comparison between strings that
ignores case differences? Answers : equalsIgnoreCase( ) method.
What is the use of valueOf( ) method? Answers : valueOf( ) method converts data from its internal format into a
human-readable form.
What are the uses of toLowerCase( ) and toUpperCase( ) methods? Answers : The method toLowerCase( ) converts all the characters in a string
from uppercase to
lowercase.
The method toUpperCase( ) converts all the characters in a string from
lowercase to
uppercase.
Which method can be used to find out the total allocated capacity of a
StrinBuffer? Answers : capacity( ) method.
Which method can be used to set the length of the buffer within a
StringBuffer object? Answers : setLength( ).
What is the difference between String and StringBuffer? Answers : String objects are constants, whereas StringBuffer objects are not.
String class supports constant strings, whereas StringBuffer class supports
growable, modifiable strings.
What are wrapper classes? Answers : Wrapper classes are classes that allow primitive types to be accessed
as objects.
Which of the following is not a wrapper class?
String
Integer
Boolean
Character Answers : a.
What is the output of the following program?
public class Question {
public static void main(String args[]) {
String s1 = "abc";
String s2 = "def";
String s3 = s1.concat(s2.toUpperCase( ) );
System.out.println(s1+s2+s3);
}
}
abcdefabcdef
abcabcDEFDEF
abcdefabcDEF
None of the above Answers : c.
Which of the following methods are methods of the String class?
delete( )
append( )
reverse( )
replace( ) Answers : d.
Which of the following methods cause the String object referenced by s to
be changed?
s.concat( )
s.toUpperCase( )
s.replace( )
s.valueOf( ) Answers : a and b.
String is a wrapper class?
True
False Answers : b.
17) If you run the code below, what gets printed out?
String s=new String("Bicycle");
int
iBegin=1;
char
iEnd=3;
System.out.println(s.substring(iBegin,iEnd));
Bic
ic
c) icy
d) error: no method matching substring(int,char) Answers : b.
18) Given the following declarations
String s1=new String("Hello")
String
s2=new String("there");
String
s3=new String();
Which of the following are legal operations?
s3=s1 + s2;
s3=s1 - s2;
c) s3=s1 & s2
d) s3=s1 && s2 Answers : a.
19) Which of the following statements are true?
The String class is implemented as a char array, elements are addressed
using the stringname[] convention
b) Strings are a primitive type in Java that overloads the + operator for
concatenation
c) Strings are a primitive type in Java and the StringBuffer is used as the
matching wrapper type
d) The size of a string can be retrieved using the length property. Answers : b.
EXPLORING JAVA.LANG
java.lang package is automatically imported into all programs.
True
False Answers : a
What are the interfaces defined by java.lang? Answers : Cloneable, Comparable and Runnable.
What are the constants defined by both Flaot and Double classes? Answers : MAX_VALUE,
MIN_VALUE, NaN,
POSITIVE_INFINITY,
NEGATIVE_INFINITY and
TYPE.
What are the constants defined by Byte, Short, Integer and Long? Answers : MAX_VALUE,
MIN_VALUE and
TYPE.
What are the constants defined by both Float and Double classes? Answers : MAX_RADIX,
MIN_RADIX,
MAX_VALUE,
MIN_VALUE and
TYPE.
What is the purpose of the Runtime class? Answers : The purpose of the Runtime class is to provide access to the Java
runtime system.
What is the purpose of the System class? Answers : The purpose of the System class is to provide access to system
resources.
Which class is extended by all other classes? Answers : Object class is extended by all other classes.
Which class can be used to obtain design information about an object? Answers : The Class class can be used to obtain information about an object’s
design.
Which method is used to calculate the absolute value of a number? Answers : abs( ) method.
What are E and PI? Answers : E is the base of the natural logarithm and PI is the mathematical
value pi.
Which of the following classes is used to perform basic console I/O?
System
SecurityManager
Math
Runtime Answers : a.
Which of the following are true?
The Class class is the superclass of the Object class.
The Object class is final.
The Class class can be used to load other classes.
The ClassLoader class can be used to load other classes. Answers : c and d.
Which of the following methods are methods of the Math class?
absolute( )
log( )
cosine( )
sine( ) Answers : b.
Which of the following are true about the Error and Exception classes?
Both classes extend Throwable.
The Error class is final and the Exception class is not.
The Exception class is final and the Error is not.
Both classes implement Throwable. Answers : a.
Which of the following are true?
The Void class extends the Class class.
The Float class extends the Double class.
The System class extends the Runtime class.
The Integer class extends the Number class. Answers : d.
17) Which of the following will output -4.0
System.out.println(Math.floor(-4.7));
System.out.println(Math.round(-4.7));
System.out.println(Math.ceil(-4.7));
d) System.out.println(Math.Min(-4.7)); Answers : c.
18) Which of the following are valid statements
a) public class MyCalc extends Math
b) Math.max(s);
c) Math.round(9.99,1);
d) Math.mod(4,10);
e) None of the above. Answers : e.
19) What will happen if you attempt to compile and run the following code?
Integer ten=new Integer(10);
Long
nine=new Long (9);
System.out.println(ten
+ nine);
int
i=1;
System.out.println(i
+ ten);
19 followed by 20
19 followed by 11
Error: Can't convert java lang Integer
d) 10 followed by 1 Answers : c.
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