Java Technical Interview Question and Answers

Java Technical Interview Question and Answers.

Question: What if the main method is declared as private?
Question: What if the static modifier is removed from the signature of the main
method?
Question: What if I write static public void instead of public static void?
Q:Question:What if I do not provide the String array as the argument to the
method?
Question: What is the first argument of the String array in main method?
Question: If I do not provide any arguments on the command line, then the String
array of Main method will be empty of null?
Question: How can one prove that the array is not null but empty?
Question: What environment variables do I need to set on my machine in order to
be able to run Java programs?
Question: Can an application have multiple classes having main method?
Question: Can I have multiple main methods in the same class?
Question: Do I need to import java.lang package any time? Why ?
Question: Can I import same package/class twice? Will the JVM load the package
twice at runtime?
Question: What are Checked and UnChecked Exception?
Question: What is Overriding?
Question: What are different types of inner classes?
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.
[ Received from Sandesh Sadhale] TOP
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”.
[ Received from Sandesh Sadhale] TOP
Q:What if I write static public void instead of public static void?
A:Program compiles and runs properly.
[ Received from Sandesh Sadhale] TOP
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”.
[ Received from Sandesh Sadhale] TOP
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.
[ Received from Sandesh Sadhale] TOP
Q:If I do not provide any arguments on the command line, then the String
array of Main method will be empty of null?
A:It is empty. But not null.

Q:How can one prove that the array is not null but empty?
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.
[ Received from Sandesh Sadhale] TOP
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.
[ Received from Sandesh Sadhale] TOP
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.
[ Received from Sandesh Sadhale] TOP
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.
[ Received from Sandesh Sadhale] TOP
Q:Do I need to import java.lang package any time? Why ?
A:No. It is by default loaded internally by the JVM.
[ Received from Sandesh Sadhale] TOP
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.
[ Received from Sandesh Sadhale] TOP
Q:What are Checked and UnChecked Exception?
A: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.
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