Possible java interview questions

Most possible java interview questions

Q:	What is final?
A:	A final class can't be extended ie., final class may not be subclassed. A final method can't be overridden when its class is inherited. You can't change value of a final variable (is a constant).
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.

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".

Q:	What if I write static public void instead of public static void?
A:	Program compiles and runs properly.

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".

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.

Q:	If I do not provide any arguments on the command line, then the String array of Main method will be empty or null?
A:	It is empty. But not null.

Q:	How can one prove that the array is not null but empty using one line of code?
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.

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.

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.

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.

Q:	Do I need to import java.lang package any time? Why ?
A:	No. It is by default loaded internally by the JVM.

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.

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.