Difference between Static methods and Instance methods

Question

I was just reading over the text given to me in my textbook and I m not really sure I understand what it is saying  It s basically telling me that static methods or class methods include the  quot modifier quot  keyword static  But I don t really know what that means  Could someone please explain to me in really simple terms what Static or Class Methods are  Also  could I get a simple explanation on what Instance methods are  This is what they give me in the textbook   There are important practical implications of the presence or absence of the static modifier  A public class method may be invoked and executed as soon as Java processes the definition of the class to which it belongs  That is not the case for an instance method  Before a public instance method may be invoked and executed  an instance must be created of the class to which it belongs  To use a public class method  you just need the class  On the other hand  before you can use a public instance method you must have an instance of the class  The manner in which a static method is invoked within the definition of another method varies according to whether or not the two methods belong to the same class  In the example above  factorial and main are both methods of the MainClass class  As a result  the invocation of factorial in the definition of main simply references the method name   quot factorial quot

User · Answer

Methods and variables that are not declared as static are known as instance methods and instance variables. To refer to instance methods and variables, you must instantiate the class first means you should create an object of that class first.For static you don't need to instantiate the class u can access the methods and variables with the class name using period sign which is in (.)

for example:

Person.staticMethod();           //accessing static method.

for non-static method you must instantiate the class.

Person person1 = new Person();   //instantiating
person1.nonStaticMethod();       //accessing non-static method.

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Instance method vs Static method   Instance method can access the instance methods and instance variables directly  Instance method can access static variables and static methods     directly  Static methods can access the static variables and static methods     directly  Static methods can   t access instance methods and instance variables     directly  They must use reference to object  And static method can   t     use this keyword as there is no instance for    this    to refer to

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The basic paradigm in Java is that you write classes  and that those classes are instantiated  Instantiated objects  an instance of a class  have attributes associated with them  member variables  that affect their behavior  when the instance has its method executed it will refer to these variables  However  all objects of a particular type might have behavior that is not dependent at all on member variables  these methods are best made static  By being static  no instance of the class is required to run the method  You can do this to execute a static method  MyClass staticMethod        Simply refers to the class s static code  But to execute a non-static method  you must do this  MyClass obj   new MyClass     Create an instance obj nonstaticMethod        Refer to the instance s class s code  On a deeper level the compiler  when it puts a class together  collects pointers to methods and attaches them to the class  When those methods are executed it follows the pointers and executes the code at the far end  If a class is instantiated  the created object contains a pointer to the  quot virtual method table quot   which points to the methods to be called for that particular class in the inheritance hierarchy  However  if the method is static  no  quot virtual method table quot  is needed  all calls to that method go to the exact same place in memory to execute the exact same code  For that reason  in high-performance systems it s better to use a static method if you are not reliant on instance variables

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If state of a method is not supposed to be changed or its not going to use any instance variables   You want to call method without instance   If it only works on arguments provided to it   Utility functions are good instance of static methods  i e math pow    this function is not going to change the state for different values  So it is static

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Instance methods   gt  invoked on specific instance of a specific class  Method wants to know upon which class it was invoked  The way it happens there is a invisible parameter called  this   Inside of  this  we have members of instance class already set with values   This  is not a variable  It s a value  you cannot change it and the value is reference to the receiver of the call  Ex  You call repairmen instance method  to fix your TV actual program   He comes with tools  this  parameter   He comes with specific tools needed for fixing TV and he can fix other things also  In static methods   gt  there is no such thing as  this   Ex  The same repairman  static method   When you call him you have to specify which repairman to call like electrician   And he will come and fix your TV only  But  he doesn t have tools to fix other things  there is no  this  parameter   Static methods are usually useful for operations that don t require any data from an instance of the class  from   this   and can perform their intended purpose solely using their arguments

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Static methods  variables belongs to the whole class  not just an object instance  A static method  variable is associated with the class as a whole rather than with specific instances of a class  Each object will share a common copy of the static methods  variables  There is only one copy per class  no matter how many objects are created from it

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The static modifier when placed in front of a function implies that only one copy of that function exists  If the static modifier is not placed in front of the function then with every object or instance of that class a new copy of that function is made     Same is the case with variables

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In short  static methods and static variables are class level where as instance methods and instance variables are instance or object level   This means whenever a instance or object  using new ClassName    is created  this object will retain its own copy of instace variables  If you have five different objects of same class  you will have five different copies of the instance variables  But the static variables and methods will be the same for all those five objects  If you need something common to be used by each object created make it static  If you need a method which won t need object specific data to work  make it static  The static method will only work with static variable or will return data on the basis of passed arguments   class A       int a      int b       public void setParameters int a  int b           this a   a          this b   b            public int add            return this a   this b            public static returnSum int s1  int s2           return  s1   s2             In the above example  when you call add   as   A objA   new A    objA setParameters 1 2     since it is instance method  call it using object objA add       returns 3   B objB   new B    objB setParameters 3 2   objB add       returns 5    calling static method    since it is a class level method  you can call it using class itself A returnSum 4 6     returns 10  class B      int s 8      int t   8      public addition int s int t          A returnSum s t    returns 16           In first class  add   will return the sum of data passed by a specific object  But the static method can be used to get the sum from any class not independent if any specific instance or object  Hence  for generic methods which only need arguments to work can be made static to keep it all DRY

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Difference between Static methods and Instance methods   Instance method are methods which require an object of its class to be created before it can be called  Static methods are the methods in Java that can be called without creating an object of class  Static method is  declared with static keyword  Instance method is not with static keyword  Static method means which will exist as a single copy for a class  But instance methods exist as multiple copies depending on the number of instances created for that class   Static methods can be invoked by using class reference  Instance or non static methods are invoked by using object reference   Static methods can   t access instance methods and instance variables directly  Instance method can access static variables and static methods directly    Reference   geeksforgeeks

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The behavior of an object depends on the variables and the methods of that class  When we create a class we create an object for it  For static methods  we don t require them as static methods means all the objects will have the same copy so there is no need of an object  e g   Myclass get      In instance method each object will have different behaviour so they have to call the method using the object instance  e g   Myclass x   new Myclass    x get

[java] Difference between Static methods and Instance methods

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