TYPES OF METHODS , SCOPE AND LIFETIME OF A VARIABLE.


As per the Sun Micro Systems , methods are classified into three categories .

       1. Mutable Methods

       2. Immutable Methods

       3. Initialiser Methods

1 . Mutable methods : 

  • The methods which are used to change the state of the fields ( that is , the values of the fields) , then those methods are known as Mutable methods .
  • The Mutable methods not only changes the values of the instance fields , but also changes the state of the local variables .
  • Mutable methods are also known as the Setter methods .
  • Mutable methods are nothing but a normal methods to a class , they act same as a instance methods to a class , but Mutable method changes the values of the fields .

2. Immutable Methods :

  • Immutable Methods are nothing but , they just print the values of the instance fields . That is , immutable methods retrieve the values from the fields .
  • In shortly , Immutable methods are the methods which do not cause any change to the fields and values , it just print the values or retrieving the data .
  • Immutable methods are also known as Getter methods .   
     Well you will get a clear idea by seeing the below programs .
Before going into the program , i need to tell you a small concept of assigning the instance values through the instance methods of a class.
We can assign the instance fields through the methods , that is by using the local variables of a method , we can assign the values of the local variables to the instance  variables . Which is nothing but the assigning the values to the instance fields are known as Mutable methods . 

PROGRAM ON MUTABLE AND IMMUTABLE METHODS : 

PROGRAM 2 :    finding the result of a student

MEMORY ALLOCATION

memory allocation for StudentResult program

Here the cross mark on the method refers that, when ever the controller comes out of the method , the values which is stored in x , y , z will be deleted  with no doubt ,but the values inside the objects will not be deleted . In simple variables are created when their method is called and deleted  when their method is left .that is the variable will not hold its value once the controller comes out f the method or scope.

As you can see the above programs existed with mutable method and immutable method . Guess your answer which is mutable and immutable method in each program . IF you are not getting , just comment or ping my blog i always stays on my blog .

Now while coming to scope and life time of a variables , scope is nothing but a block of code which is contained within the curly braces . And the variables are nothing but the local variables declared inside the scope . In Java methods will also acts as scope and the variables declared inside the methods are called local variables .

Now the above  explanation will be technically explained in the below topic scope and life time of a variable .

SCOPE AND LIFE TIME OF VARIABLES :

  • A block which is beginning with opening curly brace and ended with closing curly brace , then that block is said to be scope . Thus , each time you start a new block , you are creating a new scope .
  • A scope determines what objects are visible to other parts of your program . It also determines the lifetime of those objects.

May other computer programming languages define two general categories of scope : global and local .However , these traditional scopes do not fit well with Java’s strict , object-oriented model . In Java , the two major scopes are those defined by a class and those defined by a method . If the method contains the parameters than that parameters are also included in the method scope .

LIFE TIME OF VARIABLES :  

Variables are created when their scope is entered, and destroyed when their scope is left . This means that a variable will not hold it’s values once it has gone out of scope .Therefore , variables declared within a method will not hold their values between calls to that method. Also , a variable declared within the block will lose it’s values when the block is left. Thus the life time of the variable is confined to it’s scope .

If a variable declaration includes an initialiser , then that variable will be reinitialised each time the block is in which is declared is entered . For example , consider the following program .

scope and life time of the variables

As you can see , ‘y’ is reinitialised to -1 each time the inner for loop is entered .

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2 responses

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