Core Java: Interview Questions and Answers
- What is the most important feature of Java?
Java is a platform independent language.
- What do you mean by platform independence?
Platform
independence means that we can write and compile the java code in one platform
(eg Windows) and can execute the class in any other supported platform eg
(Linux,Solaris,etc).
- What is a JVM?
JVM
is Java Virtual Machine which is a run time environment for the compiled java
class files.
- Are JVM's platform independent?
JVM's
are not platform independent. JVM's are platform specific run time
implementation provided by the vendor.
- What is the difference between a JDK and a JVM?
JDK
is Java Development Kit which is for development purpose and it includes
execution environment also. But JVM is purely a run time environment and hence
you will not be able to compile your source files using a JVM.
- What is a pointer and does Java support pointers?
Pointer
is a reference handle to a memory location. Improper handling of pointers leads
to memory leaks and reliability issues hence Java doesn't support the usage of
pointers
- What is the base class of all classes?
java.lang.Object
- Does Java support multiple inheritance?
Java
doesn't support multiple inheritance.
- Is Java a pure object oriented language?
Java
uses primitive data types and hence is not a pure object oriented language.
- Are arrays primitive data types?
In
Java, Arrays are objects.
- What is difference between Path and Classpath?
Path
and Classpath are operating system level environment variales. Path is used
define where the system can find the executables(.exe) files and classpath is
used to specify the location .class files.
- What are local variables?
Local
varaiables are those which are declared within a block of code like methods.
Local variables should be initialised before accessing them.
- What are instance variables?
Instance
variables are those which are defined at the class level. Instance variables
need not be initialized before using them as they are automatically initialized
to their default values.
- How to define a constant variable in Java?
The
variable should be declared as static and final. So only one copy of the
variable exists for all instances of the class and the value can't be changed
also.
static final int MAX_LENGTH = 50; is an example for constant.
- Should a main() method be compulsorily declared in all
java classes?
No
not required. main() method should be defined only if the source class is a
java application.
- What is the return type of the main() method?
Main()
method doesn't return anything hence declared void.
- Why is the main() method declared static?
main()
method is called by the JVM even before the instantiation of the class hence it
is declared as static.
- What is the arguement of main() method?
main()
method accepts an array of String object as arguement.
- Can a main() method be overloaded?
Yes.
You can have any number of main() methods with different method signature and
implementation in the class.
- Can a main() method be declared final?
Yes.
Any inheriting class will not be able to have it's own default main() method.
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