Class and Interface

Although I want to write full article for a topic in JAVA but today I felt, some times small tips are more important than a full page theory when you want to revise quickly like for an interview ;)

I’m writing here few notes which I have collected while reading Java Books and hope these would be helpful for you too.

Final Classes:

• String Class can’t be sub classed.
• Final class obliterates a key benefit of OOP – Extensibility.
• Final class uses for safety and security.

Abstract Classes:

• In abstract class, method marked abstract end in a semicolon(;) rather than curly braces.
• If you change a method from abstract to non-abstract then you need to change the semicolon at the end of the method declaration into a curly braces pair.

Interface:

• All the interface method must be implemented and must be public and abstract(implicitly it is already done).
• An interface is an 100% abstract class.
• But an abstract class can have abstract or non-abstract methods, while an interface can have only abstract methods (this is the difference).
• All variable defined in an interface must be public , static and final it means interface can declare only constants, not instance variables.
• Interface methods must not be static as interfaces defines instance methods.
• You can’t change the value of constant or variable defined in interface from implementing class, it will give compiler error.

Methods of Class Object:

• Boolean equals(object obj)
• void finalize()
• int hashcode()
• final void notify()
• final void notifyall()
• final void wait()
• String toString()

toString() method:

• This method simply spit out object state(or in other words) get the current values of the important instance variable.
• When you pass an object reference to System.out.println() method it will call object.toString() method implicitly.

Hope you liked the tips, I will give move tips in my next post so don’t forget to give your feedback/comments as it motivates me to write more.
C YA BUDDY!!!