Most Common Interview Questions
Q1. What are the various access specifiers for Java classes?
Ans:
In Java, access specifiers are the keywords used before a class name which
defines the access scope. The types of access specifiers for classes are:
1.
Public : Class,Method,Field is accessible from anywhere.
2.
Protected:Method,Field can be accessed from the same class to which they belong
or from the sub-classes,and from the class of same package,but not from
outside.
3.
Default: Method,Field,class can be accessed only from the same package and not
from outside of it's native package.
4.
Private: Method,Field can be accessed from the same class to which they belong.
Q2. What's the purpose of Static methods and static variables?
Ans:
When there is a requirement to share a method or a variable between multiple
objects of a class instead of creating separate copies for each object, we use
static keyword to make a method or variable shared for all objects.
Q3. What are Loops in Java? What are three types of loops?
Ans:
Looping is used in programming to execute a statement or a block of statement
repeatedly. There are three types of loops in Java:
1)
For Loops
For
loops are used in java to execute statements repeatedly for a given number of
times. For loops are used when number of times to execute the statements is
known to programmer.
2)
While Loops
While
loop is used when certain statements need to be executed repeatedly until a
condition is fulfilled. In while loops, condition is checked first before
execution of statements.
3)
Do While Loops
Do
While Loop is same as While loop with only difference that condition is checked
after execution of block of statements. Hence in case of do while loop,
statements are executed at least once.
Q4. What is the difference between double and float variables in Java?
Ans:
In java, float takes 4 bytes in memory while Double takes 8 bytes in memory.
Float is single precision floating point decimal number while Double is double
precision decimal number.
Q5. What's the difference between an Abstract Class and Interface in Java?
Ans:
The primary difference between an abstract class and interface is that an
interface can only possess declaration of public static methods with no
concrete implementation while an abstract class can have members with any
access specifiers (public, private etc) with or without concrete
implementation.
Another
key difference in the use of abstract classes and interfaces is that a class
which implements an interface must implement all the methods of the interface
while a class which inherits from an abstract class doesn't require
implementation of all the methods of its super class.
A
class can implement multiple interfaces but it can extend only one abstract
class.
Q6. How garbage collection is done in Java?
Ans:
In java, when an object is not referenced any more, garbage collection takes
place and the object is destroyed automatically. For automatic garbage
collection java calls either System.gc() method or Runtime.gc() method.
Q7.Name some OOPS Concepts in Java?
Java is based on Object
Oriented Programming Concepts, following are some of the OOPS concepts
implemented in java programming.
·
Abstraction
·
Encapsulation
·
Polymorphism
·
Inheritance
·
Association
·
Aggregation
·
Composition
Q8.What is the difference between JDK and JVM?
Java Development Kit (JDK) is for development purpose and JVM is a
part of it to execute the java programs.
JDK provides all the tools,
executables and binaries required to compile, debug and execute a Java Program.
The execution part is handled by JVM to provide machine independence.
Q9.What is the difference between JVM and JRE?
Java Runtime Environment (JRE) is the implementation of JVM. JRE
consists of JVM and java binaries and other classes to execute any program
successfully. JRE doesn’t contain any development tools like java compiler,
debugger etc. If you want to execute any java program, you should have JRE
installed.
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