Declaration and Access Control - Quick Reference

Java Job Interview Questions - Quick Reference Points / Points to Remember

Declaration and Access Control - Quick Reference

Ø There can be only one public class per a source code file.

Ø The name of the source code file must be same as the public class in that file.

Ø A class file should first have a package name (if any) , then import statements (if any) and class declaration.

Ø A class can be marked either as public or with no access modifier, which specifies package (default) access.

Ø A class can be marked as strictfp, final or abstract.

Ø A class can not be declared as private or protected.

Ø A class cannot be marked as both abstract and final.

Ø A final class cannot be sub classed ( extended)

Ø An abstract class must be sub classed.

Ø An abstract class cannot be instantiated i.e it is not possible to create an object of an abstract class.

Ø Marking a class as final is to avoid overriding of its method in subclasses.

Ø An abstract class is used to define a generic behaviour of an object.

Ø If any method of a class is abstract, whole class must be marked as abstract.

Ø A class can be abstract even if there are no abstract methods.

Ø Abstract methods ends with a semicolon.

Ø Abstract classes let us to use polymorphism.

Ø Methods and instance variables of a class is collectively known as members of a class.

Ø Members of a class can have four different access levels – public, protected, default and
private.

Ø public – Access Anywhere

Ø protected – Access in the same package and in subclasses.

Ø default (no access modifier) – Access inside same package.

Ø private – Access inside same class.

Ø A member marked as private cannot be accessed outside the same class.