HCL Interview Questions Part-2
What if the main method is declared as private?What if the static modifier is removed from the signature of the main method?
What if I write static public void instead of public static void?
What if I do not provide the String array as the argument to the method?
What is the first argument of the String array in main method?
If I do not provide any arguments on the command line, then the String array of Main method will be empty or null?
How can one prove that the array is not null but empty using one line of code?
What environment variables do I need to set on my machine in order to be able to run Java programs?
Can an application have multiple classes having main method?
Can I have multiple main methods in the same class?
Do I need to import java.lang package any time? Why ?
Can I import same package/class twice? Will the JVM load the package twice at runtime?
What are Checked and UnChecked Exception?
What is Overriding?
What are different types of inner classes?
What if the main method is declared as private?
What if the static modifier is removed from the signature of the main method?
What if I write static public void instead of public static void?
What if I do not provide the String array as the argument to the method?
What is the first argument of the String array in main method?
If I do not provide any arguments on the command line, then the String array of Main method will be empty or null?
What environment variables do I need to set on my machine in order to be able to run Java programs?
Can an application have multiple classes having main method?
Can I have multiple main methods in the same class?
Do I need to import java.lang package any time? Why ?
Can I import same package/class twice? Will the JVM load the package twice at runtime?
What are Checked and UnChecked Exception?
If I do not provide any arguments on the command line, then the String array of Main method will be empty or null?
How can one prove that the array is not null but empty using one line of code?
What environment variables do I need to set on my machine in order to be able to run Java programs?
Can an application have multiple classes having main method?
Can I have multiple main methods in the same class?
Do I need to import java.lang package any time? Why ?
Can I import same package/class twice? Will the JVM load the package twice at runtime?
What are Checked and UnChecked Exception?
What is Overriding?
What are different types of inner classes?
What if the main method is declared as private?
The program
compiles properly but at runtime it will give "Main method not
public." message.
[capptitudebank.blogspot.com]
What if the static modifier is removed from the signature of the main method?
Program
compiles. But at runtime throws an error "NoSuchMethodError".
[capptitudebank.blogspot.com]
What if I write static public void instead of public static void?
Program
compiles and runs properly.
[capptitudebank.blogspot.com]
What if I do not provide the String array as the argument to the method?
Program
compiles but throws a runtime error "NoSuchMethodError".
[capptitudebank.blogspot.com]
What is the first argument of the String array in main method?
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.
[capptitudebank.blogspot.com]
If I do not provide any arguments on the command line, then the String array of Main method will be empty or null?
It is
empty. But not null.
[capptitudebank.blogspot.com]
How can one prove that the array is
not null but empty using one line of code?
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.
[capptitudebank.blogspot.com]
What environment variables do I need to set on my machine in order to be able to run Java programs?
CLASSPATH
and PATH are the two variables.
[capptitudebank.blogspot.com]
Can an application have multiple classes having main method?
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.
[capptitudebank.blogspot.com]
Can I have multiple main methods in the same class?
No the
program fails to compile. The compiler says that the main method is already
defined in the class.
[capptitudebank.blogspot.com]
Do I need to import java.lang package any time? Why ?
No. It is
by default loaded internally by the JVM.
[capptitudebank.blogspot.com]
Can I import same package/class twice? Will the JVM load the package twice at runtime?
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.
[capptitudebank.blogspot.com]
What are Checked and UnChecked Exception?
A checked
exception is some subclass of Exception (or Exception itself), excluding class
RuntimeException and its subclasses.
Making an exception checked forces client programmers to
deal with the possibility that the exception will be thrown. eg, IOException
thrown by java.io.FileInputStream's read() method•
Unchecked exceptions are RuntimeException and any of its
subclasses. Class Error and its subclasses also are unchecked. With an
unchecked exception, however, the compiler doesn't force client programmers
either to catch the
exception or declare it in a throws clause. In fact, client
programmers may not even know that the exception could be thrown. eg,
StringIndexOutOfBoundsException thrown by String's charAt() method• Checked
exceptions must be caught at compile time. Runtime exceptions do not need to
be. Errors often cannot be.
What is Overriding?
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.
What are different types of inner
classes?
Nested
top-level classes, Member classes, Local classes, Anonymous classes Nested
top-level classes- If you declare a class within a class and specify the static
modifier, the compiler treats the class just like any other top-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. Top-level inner classes implicitly have access only to static
variables.There can also be inner interfaces. All of these are of the nested
top-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 top-level class. The primary difference between
member classes and nested top-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.
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