What is difference between method and constructor in Java is
very common questions on beginner level Java
interviews with 2 to 3 year experience. Since constructor is kind of
special and it has it's own properties which separates it from any normal Java method,
this question make sense. Main difference between Constructor and Method is that,
you need to call method explicitly but constructor is called implicitly by Java
programming language during object instantiation. It doesn't mean you can not
call Constructor; if you have overloaded
constructor than you can call them using this
keyword as this() constructor, you can even call
super class constructor using super() keyword, in-fact that is
done automatically by Java compiler if no explicitly constructor is called and
that is known as constructor chaining in Java. Like many other beginner
level questions e.g. Vector
vs ArrayList, We will see difference
between method and constructor in Java in point form to understand
important properties of each of them clearly.
Method vs Constructor in Java
Both method and constructor wraps
bunch of code but constructor is very different than normal method in Java.
Before seeing difference between Constructor and Method, let's see some common
things between them.
1) Both method and Constructor can be overloaded
or overridden
in Java. Though calling mechanism of Constructor is different than method. you
can call an overloaded constructor as this(argument) or super(argument) based upon
whether its declared on same class or super class but for calling overloaded
method or overridden
method, you simply use method name.
2) You can make your constructor public, protected, private similar to
your method in Java. By the way If you are not familiar with access modifier
in Java than see Difference
between public, protected and private keyword in Java.
Now let's see some important difference
between method and constructor in Java :
1) First difference between method vs constructor in Java is
that name of constructor must be same with name of the Class but
there is no such requirement for method in Java. methods can have any arbitrary
name in Java.
2) Second difference between method and constructor in Java is that constructor
doesn't have any return type but method has return type and return
something unless its void.
3) Third difference between constructor and method in Java is that
Constructors are chained and they are called in a particular order, there is no
such facility for methods.
4) Unlike method, constructor, yet declared in class doesn't considered
as member
of Class. Constructors are not inherited by child classes but methods are
inherited by child classes until they are made private. on which
case they are only visible in class on which they are declared. Similarly private
constructor means you can not create object of that class from outside, this is
one of the technique used to implement Singleton
pattern in Java.
5) Another difference between method and constructor in Java is that
special keyword this and super is used to
call constructor explicitly. no such thing for method, they have there own name
which can be used to call them.
That's all on difference between method and constructor in Java. You can
compare method vs Constructor on different points but main thing is that they are used for object
initialization, while method is used to perform a small unit of task.
Other Java fundamental tutorial from java67 site
Difference
between Serializable and Externalizable in Java
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